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Патент USA US3039589

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June 19, 1962
5 Sheets-Sheet 1
Filed Sept. 28, 1959
June 19, 1962
Filed Sept. 28, 1959
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5 Sheets-Sheet 2
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June 19, 1962
5 Sheets-Sheet 3
Filed Sept. 28, 1959
jam DAVID N _ ST /
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June 19, 1962
$401 w
United States Patent
0 f 1C6
FIGURES 2A, 2B, 2C, 2D and 2E are component
portions of the circuit for controlling change-over be
tween the two driving mechanisms.
iFIGURE 3 shows the foot locking arrangement in
Joseph Kenneth Royle, Heaton Moor, Stoekport, and
Brian David Nellist, Manchester, England, assignors
cross section on an enlarged scale.
to National Research Development Corporation, Lon
don, England, a British corporation
Filed Sept. 28, 1959, Ser. No. 842,815
Claims priority, application Great Britain Oct. 2, 1958
is required.
This invention relates to apparatus for driving a ?rst
object along a predetermined path in relation to a second
FIGURE 5 shows a modi?cation of the circuitry shown
in FIGURES 2B, 2C, 2D and 2E.
FIGURE 6‘ shows an enlarged detailed arrangement
of the locking device.
object ‘and is particularly applicable to the propulsion of
the slides of machine tools along their slideways though
According to the invention there is provided driving
apparatus for causing relative movement along a predeter
mined path 1between a ?rst object and a second object,
FIGURE 4 shows an embodiment, of the invention
which is a modi?cation of the embodiment illustrated in
FIG. 1 in that only one main hydraulic control valve
17 Claims. (Cl. 192-143)
the invention is not con?ned to such applications.
Patented June 19, 1962
FIGURE 7 is a circuit modi?cation.
A work table 1 is mounted on a slideway (not shown)
carried by a bed 2. Both drives are similarly mounted so
that the mounting of the ?rst drive only need be de
scribed. Cylinder CI is fast with the work table 1.
comprising a ?rst driving mechanism and a second driving
Piston PI rides in CI and is ‘fast with the piston rod
mechanism (hereinafter respectively called “the ?rst 20 emerging from both ends of CI through glands in the
drive” and “the second drive”) each such mechanism in
cylinder ends. The outer ends of this piston rod are
turn comprising two members between which relative
secured to brackets upstanding from a foot FI which
movement takes place to provide the driving action of
rides on a slideway integral with the machine bed 2
the mechanism, the ?rst of such members being secured
and parallel to the slideway carrying table 1. Means
to the ?rst object and the second of such members being 25 described below in relation to FIGURE 3 are provided
for releasably locking foot F1 to the slideway. Fll of
provided with means (hereinafter called the “locking
means”) for releasably securing it to the second, object at
the second drive rides along the same slideway as FI and
different positions along -a track parallel to the said pre
the second drive is displaced ‘from the ?rst drive along
determined path, means (hereinafter called the “actuating
the direction of movement of table 1 along its said slide
means”) adapted in response to an incoming driving sig 30 ways on bed 2, which may be the same slideways as those
nal to initiate driving action on the part of the driving
along which FI and F11 ride.
The cylinders CI and C11 have associated hydraulic
mechanism means (hereinafter called the “positioning
means”) for positioning the ?rst member relative to the
valves VI and VII actuated by actuators AI and All
second member when the driving mechanism in question
‘One of the drives is required to drive the table whilst
is not executing a driving ‘action and means (hereinafter 35
called the “indicating means”) for indicating the relative
the foot of the other is unlocked and when this drive
positions of the two members at least ‘at a plurality of
approaches the end of its stroke its place is taken by the
predetermined relative positions of the two members, the
other drive which has in the meantime had its piston posi
apparatus further comprising means for operating the
tioned so as to have a substantial part of its stroke avail—
locking means of the ?rst drive and releasing the locking 40 able for driving action in the direction in which the work
means of the second drive, means for applying driving
table is for the moment travelling. The changeover be
signals to the ?rst driving actuating means, means for
tween the two drives involves the locking of the foot
actuating the second drive positioning means to place the .
of the drive which is about to take over the driving func
members of the second drive in predetermined relative
tion and the unlocking of the foot of the drive which is
positions, means under control of the ?rst drive indicating
relinquishing the driving function. The driving signals
means for operating the second drive locking means and
must also be transferred from the actuator of the latter
bringing the second drive actuating means under control
of the driving signals and means, operable when the lock
ing means of both drives are operated and before either
of the driving mechanisms has reached an end of its range
of driving action, ‘for releasing the locking means of that
drive to that of the former drive.
In practice it is necessary that there should be an
interval when for a short time both drives are participat
ing in the driving action with their feed looked, so that
there shall not be a period at the time of change-over
one of the two driving mechanisms which is nearest to an
when both the feet are unlocked since this would leave
end of its driving range which it is at that instant ap
the table out of control.
proaching in the course of its driving action and remov
Suppose that the ?rst drive is operating to move table
ing the actuating means of that driving mechanism from 55 1 to the right and the second drive is idling.
the control of the driving signals, the ?rst drive and the
Piston PI will be moving towards the left hand end of
second drive being interchangeable ‘in respect of the func
cylinder CI. If the second drive is to take over the driv
tions of the various means ‘further comprised in the
ing function for the same direction of movement of table
apparatus as aforesaid whereby the two driving mecha
1, then its piston PII must be positioned away from the
nisms may operate in turn to produce relative movement 60 left hand end of its cylinder CII. This positioning may
between the ?rst object and the second object.
be done by suitable actuation of valve VII whose actua
The invention will ‘be more readily understood from the
tor All will not be connected to receive the driving sig
following description of certain. embodiments thereof
nals. It is preferred however to provide independent
illustrated in the accompanying drawings in which the
positioning means for the drives and this necessitates re
?rst and second objects are respectively a work table and
moving each of them from the control of its valve. To
the bed of a machine tool and in which the driving mecha
this end taps TI and ‘I'll are provided which can be op
nisms take the form of hydraulic piston cylinder units.
erated to interconnect the opposite ends of cylinder CI
The elements of the ?rst drive are all given the sui?x “I”
and cylinder 011 respectively, the hydraulic pressure be
and the elements of the second drive the suiiix “ll.”
FIGURE 1 is a diagrammatic representation of the‘ 70 ing at the same time cut off from the valves VI and VII
or the valves being dissociated from their cylinders in any
mechanical ‘arrangement of a‘?rst embodiment of the
other convenient way.
' As, at the moment under consideration, the second
drive is being positioned, T11 is open and the positioning
gratings are superimposed with a small gap between ad
jacent ?at surfaces thereof and are mounted so that they
means may be arranged to move PII a substantial part of
remain in overlapping relationship and with substantially
the way towards the right hand end of its stroke.
uniform spacing between the said ?at surfaces, in all po
sitions of the table along its slideway. When a light
source is viewed through both gratings dark bands (so
Indicating means associated with the ?rst drive now
indicate that PI is approaching the left hand end of its
stroke. PII having been positioned as aforesaid, PH
is now locked, and the signal ‘for this to take place may
called moiré fringes) running transversely of the rulings ,
of the gratings are seen.
These bands may be scanned
be the coincidence of the said indication of the position
through a slit running parallel to the bands, by means of
of PI and a similar indication that PII has been positioned 10 a light cell. When the gratings make relative movements
‘as aforesaid. At the instant when both feet become
on movement of the table, the bands move transversely
locked together TH may still be open, but before PI
of the gratings though at a considerably magni?ed ve
reaches the end of its stroke, VII must be connected to
locity. Such movement causes a substantially sinusoidal
receive the driving signals and TH must be closed. There
variation ‘of the output of the light cell, one cycle of such
must be a time when both drives are receiving the driving
variation corresponding to a movement of the table of a
signals to guard against any gap when neither of them
distance equal to the distance ‘between adjacent rulings are receiving driving signals, since any such gap would
of the grating. Signals in either digital or analogue form
leave table 1 out of control.
representing the actual motion of the work table can
If the sense of the driving signals remains the same,
readily be derived from the output of the light cell.
the next step is to release Fl, remove the ?rst drive from 20
A problem arises in connection with monitoring sys
control by the driving signals by disabling VI, operating.
tems of this type in that one of the gratings has. to be
TI, and conditioning the ?rst drive for control by the po
somewhat longer than the distance the table is ‘required
sitioning means. If these functions cannot take place si
to travel. This distance may amount to several feet and
multaneously they should follow one another in the order
diffraction gratings of this length are difficult to-make
25 ‘and difficult to mount.
If the driving signal calls for a change of direction of
With the arrangement of the invention, each driving
the table immediately ‘after the change-over from the ?rst
mechanism may be supplied with a separate di?raction
drive to the second drive has been completed, piston PII
grating assembly and as the travel of each drive mech
will be close to the right hand end of its stroke and it
anism is relatively short, the use of a long diffraction
will move closer still to this end of its stroke in the 30 grating may be avoided. When driving action is changed
course of driving table 1 in the new direction. This will
over from one driving mechanism to the other, the moni
bring about a rapid change-over to control by the ?rst
toring function is also changed over and the total “count”
'drive again, the sequence of events being similar to those
of fringes is asaccurately maintained as in the case of a
occurring on a change-over from the ?rst drive to the
single long diffraction grating assembly provided that steps
35 are taken to ensure that count units are not lost or
second drive, as previously described.
If the driving signal calls for a change of direction
spuriously added in due to misphasing of the two systems
of the table during the short interval of time that both
at the instant of change-over.
feet are locked and both driving mechanisms are being ,
In the embodiment illustrated in FIGURE 1 the posi
actuated by the driving signal, then it is necessary to
tioning of the unlocked foot is ensured by mechanical
arrange that the ?rst driving means resumes the driving 40 means.
function without completeing the change-over. This can
An auxiliary hydraulic cylinder C111 is mounted on the
'be arranged by selecting the foot to be released according
underside of table 1. A piston PIII capable of double
‘to which of the pistons moves towards the centre of its
acting operation, rides in G111 and is mounted on a piston
stroke during the interval when both feet are locked. For
rod 3, the ends of which pass through glands in the cyl~
instance PI, with rightwards ‘travel of table 1, had ap
inder ends of CHI and are secured to a depending cradle
proached the left hand end of its stroke and PH had been
4, the lower end of which carries a pivot on which is
positioned towards the right hand end of its stroke prior
mounted a pinion 5. This pinion engages two toothed
to the locking of both feet, in the example quoted above.
racks 6 and 7 one ‘attached to each of the feet FI and
If now the driving signal causes table 1 to move to the
F11. The piston rod extends beyond the right head end
left, PII will approach yet nearer to the right hand end 50 of the cradle and enters a valve VIII the body of which
of its stroke and PI will recede from the left hand end
is attached to table l and is provided with a bore and
of its stroke. This state of affairs must be made to se
ports for controlling the application of hydraulic ?uid
lect FII (rather than F1) to be unlocked; freeing from
. under pressure to CHI by means of a spool valve integral
control by the driving signal and conditioning of the driv
with or fastened to the end of the piston rod 3. The
ing mechanism for positioning must always be applied 55 valve VIII is so arranged that when PIII moves from the
to the drive mechanism whose foot is released. Further
more once afoot is released in this way, these other events
centre of its stroke in CIII the valve operates to'restore
it to the centre. A tap TIV controls the supply of hy
should be completed independently of any change of the
draulic fluid to VIII from the high pressure side of the
sense of the driving signal during any period of time which
system. A tap TIII interconnects the two ends of CIII
may elapse during the completion of the said events.
60 so that PIII can move without constraint when the tap
A subsidiary advantage of the invention relates to the
is open.
means for monitoring the motions made good by the ta
When P111 is held in the centre of its stroke in CHI
ble 1. Such means are commonly employed to complete
by the action of VIII, any movement by the piston of
a feedback servo loop wherein command signals repre
one of the drives relative to its cylinder, results in a
senting motions which the table is required to make are 65 movement of the piston of the other drive in the opposite
continuously compared, with due regard to sign, with
‘direction in relation to its cylinder. This can only hap
the monitoring signals, to produce a difference or error
pen when one of the feet is unlocked. When both feet
signal which is applied to the actuator of the operative
are locked, in the process ‘of changing over from the
driving mechanism. A commonly used monitoring means
comprises a pair of optical diffraction gratings, a long
grating and a short grating, one attached to the table and
the other attached to the slideway. The rulings of the
gratings run transversely of the ‘direction of motion of
the table and the two gratings have the directions of their
rulings slanted at a small angle to one another.
The 75
drive by one driving mechanism, to drive by the other,
the two racks 6 and 7 Will be locked to the bed 2 and
the pinion 5 Will also be held fast between them. To
enable this to happen, tap TIII must be open to enable
PHI to move freely in CIII as the latter moves to the
right with the table 1.
Suppose that the table has been moving to the right
for instance, driven by PI/CI and, PI having neared the
left-hand end of its stroke in CI, both feet have become
locked. During the prcvic IS movement to the right of
table 1, P111, held in its central position by VIII, will
have carried the carriage 4 and the pinion 5 bodilypto
the right, causing the pinion to rotate anti-clockwise in
rolling along rack 6. The combined rotary and bodily
simultaneously, whilst Q remains operated. Preferably
g5 contacts are adjusted to close before q3 contacts since
it is necessary that the position of VII should be under
control of All before'the tap T11 is closed since the op
eration of PII/CII would be arbitary if TII were to be
closed with VII in an arbitrary position and this might re
suit in a brief interval of time during which PII/CII was
opposing the action of PI/CI.
movement of the pinion will have driven rack 7 to the
Taps T111 and TIV are also supplied with electromag
right. The bodily movement towards the right, of the
actuators designated T111 and TIV in FIGURE 2.
pinion 5 balances the rightwards movement of C11 with
actuators are arranged to be operated one at a time
table 1 and the rotary movement of the pinion 5 increases
via change-over contacts L14. When Q is unoperated
the rightwards movement of PH so that it exceeds this
TIII is energised holding tap TIII closed; when Q is oper
rightwards movement of CH with table 1, thus causing PII
ated TIV is energised over q4 front contacts closing tap
to approach the right-hand end of CH.
Also during this time TII will have been open to free
PII from constraint by the hydraulic ?uid in CH and
AH will have been disconnected from the driving signals.
Before both feet ‘are locked, TIII must be opened, and
TIV. Thus when both feet are locked P111 is free to
move in its cylinder CIII.
The drives of FIGURE 1 are each equipped with a dif
fraction grating position monitoring system of the type
previously described. Each system has a relatively long
freed from constraint by rack 7, and as CII will still be 20 diffraction grating carried by a bracket mounted on the
top of one of the upstanding arms of the foot and a
moving to the right with table 1 this, in conjunction with
cooperating small diffraction grating together with light
the friction of FII on bed 2, would tend to move piston
source, slit, and photoelectric cell mounted on the table.
PII back towards its central position. On the other hand
light cell for F1 is designated MI and the light cell
any resistance to ?ow through TH and TIII tends to hold
PII at the right hand end of CH. It is of little moment 25 for P11 is designated MII. It is necessary to change-over
the connections to the comparator, in which the monitor
which of these tendencies predominates because the in
ing signals are compared with the command signals, from
terval is short.
one monitor system to the other when the drive is changed
The locking of both feet and the accompanying opera
from one drive to the other.
tions are initiated when both the pistons PI and P11 have
This change-over may be done by electronic means
reached corresponding positions near to the opposite ends
make the change instantaneously. As the signals
of their respective strokes. To bring this about each drive
from the two monitoring signals will only rarely be in
is provided with a pair of limit switches, 18 and 28 for
phase when both feet are locked, there will be an error
PI, CI, FI and 3S and 48 for PII, CIl, FII. These pairs
if the changeover takes place with no previous phas
of switches are operated by cams Cal and Call carried
by one of the upstanding brackets of F1 and F11 respec 35 ing operation but if the unit of distance represented by a
cycle of the monitoring means is made small in relation
to the limitsof accuracy to which the motion of the table
FIGURE 2 shows a circuit for controlling the change
is to be controlled, this misphasing error can be ignored.
over between the two driving mechanisms by means of
Over a large number of successive changes of driving ac
relays of the telephone type.
tion the errors will in any event tend to cancel one an
Contacts 181 and 281, of switches 13 and 2S respec
during any interval between the two events FII will be
tively, are arranged in parallel so that each can form an
other on a statistical basis.
It is nevertheless preferable to arrange to bring the
monitoring signals into phase before changing over and
this is preferably undertaken by an electronic phasing cir
in parallel so that each can form an operating circuit for
a relay Q in series with normally open contacts p1 of 45 cuit illustrated schematically in FIGURE 2 by the cir—
cuit denoted “Monitor phasing circuit.” This circuit is
relay P. Only when one switch of both pairs is closed
energised over (16 contacts on operation of Q and being
can Q operate. When Q operates, its normally open con
of the electronic type it can be made to respond before
operating circuit for a relay P. Contacts 381 and 481,
of switches 38 and 45 respectively, are similarly arranged
tacts q1 cause operation of a double-wound relay R over
the locking of the hitherto free foot becomes eifective.
its normally open contacts r1 complete a holding circuit, 50 Many methods are available for bringing the two moni
tor systems into phase.
prepared at p2 on operation of P, over the “holding”
One such method is to vary the relative positions of the
winding of R. The operation of Q, followed by the opera
two feet immediately prior to the locking of the hitherto
tion of R has the following results.
free foot. This may be done by a suitable shift of the‘
TI and LVI and TH and LVII each have electromag
piston PIII from its central position for in
netic actuators. These actuators are designated TI, LVI, 55 stance byofmeans
of an electromechanical transducer in
TIL LVII in FIGURE 2. When the actuators are en
serted between piston rod 3 and the valve spool of VIII,
ergised the respective taps T are closed and the foot look
a phase correction signal from the Monitor phasing cir
ing control valves LV are opened to lock the respective
cuit being applied to the transducer so as, in e?ect, to
lengthen or shorten piston rod 3. For this method to‘ be
TI and LVI are connected in parallel in a normally
effective the locking action of the hitherto free LV lock
made operating circuit over back‘ change-over contacts r2
valve must be synchronised with the opening of tap TIII
its “operate” winding, On operation of R, the closing of
whilst T11 and LVII are connected in parallel in a nor
mally open operating circuit including front change-over
so that there is no period when the foot is out of control
and free to misphase the two monitors again.
contacts r2. Contacts (13 bridge together these two oper
When the two feet have been locked, with the moni
ating circuits so that both are completed when Q is oper 65 tors in phase, the change-over between the two monitors
ated. Q operates ?rst and tap T11 is closed so that
can take place at any convenient instant so long as there
PII/CII can drive under control of VII when the driv
is no gap when no monitor is connected to the servo
ing signals are applied to its actuator AII. Also LVII is
signal comparator.
operated to lock foot FII. Immediately after the opera
The change-over is effected by change-over contacts rd
tion of Q, ‘R operates and changes over r2 but this has 70
relay R and to bridge the gap when the blade of r4 is
no elfect on the TI, LVI, TII, LVII operating circuit so
crossing the back and front contacts, both monitors MI
long as Q remains operated.
and M11 are bridged together by a temporary connection
A similar circuit comprising change-over contacts 1'3
under control of the Monitor phasing circuit, illus
and normally open contacts g5 operates to connect the
driving signals to the two main actuators AI and All 75 trated schematically in dotted lines as a relay contact set
mp. When both feet are locked and the driving sig
nals are being applied to both actuators AI and All, if
the driving signals do not change their sense, so that in
the example under discussion, they still call for right
plunger L is'forced into engagement with the bed to
lock foot F to the bed. Alternatively valve LV can be
operated to connect LC to the lowpressure or exhaust
side of the hydraulic pressure system whereupon plunger
Wards movement of table 1, then PI will move closer still
to the left hand end of its stroke and switch contacts 251
is free to slide on the bed.
will remain closed.
PII on the other hand, being po
sitioned at the right hand end of its stroke will move to
which is a modi?cation of the embdiment illustrated in
the left in relation to C11 and switch contacts 351 will
open. Q will release but R will hold over r1 and p2;
also r2, r3 and r4 will remain operated holding FII
locked by means of LVII, TII closed, AII connected to
receive the driving signals and M11 connected to the servo
signal comparator whilst the release of Q unlocks FI by
L is released from engagement with the bed and foot F
FIGURE 4 shows an embodiment of the invention
FIGURE 1 in that only one main hydraulic control valve
is required. The control circuits of FIGURE 2 may be
used with the omission of the portion FIGURE 2C.
The actuator AI for this single control valve is perma
nently connected to the servo signal generator and the
valve is connected to the two cylinders CI and CH by
means of LVI, opens TI, disconnects AI from the driv 15 ducts which effectively place the two cylinders in series.
ing signals, and~ MI from the servo signal comparator
One of these ducts, 8, connects one outlet from the valve
and on the release of g4 PIII/CIII will be restored to
VI to the right hand side of CH and another of the
normal operation by opening TIV and closing TIII, where
ducts, 9, connects the other outlet from the valve VI with
upon FII will start to move to the right under control of
the left hand side of CI. The third of the ducts, 10, con
racks 6 and 7 and pinion 5. This will soon cause switch
nects the right hand side of CI to the left hand side of
contacts 281 to open, releasing P but R will still hold
over back contacts q2 in parallel with p2, despite the
When TI is open the ducts 9 and 10 are connected
opening of p2. If there is no change in the direction of
together and the pressures on the two sides of P1 are
the driving signals the second drive will continue to drive
equalised so that cylinder CI is idle and no opposition is
table 1 to the right with relay R operated, and the ?rst 25 offered to the free movement of piston PI therein. Under
drive will be positioned so that PI moves towards the
these conditions the valve VI controls the drive CII,
right hand end of C1 whilst PII moves towards the
PII and CI, PI is free to be positioned. When, conversely,
left hand end of C11. On continued rightwards move
TI is closed and TII is open cylinder C11 is bypassed and
ment of table 1 switch contacts 451 and 151 will even
ducts 3 and it} are connected together to connect the valve
tually close and operate P and Q again, R continuing to
VI to the right hand side of CI.
hold over p2 on the opening of q2. The phasing of the
When in the course of a change-over operation, both
7 monitors will be effected and both feet will be locked as
feet FI and FII are locked and both taps TI and TII
described above in relation to the change-over from the
are closed the two pistons PI and PH become virtually
?rst drive to the second drive. If the rightwards move
one piston and hydraulic ?uid displaced from the one
ment of table 1 continues switch contacts 481 will remain
the piston of which is moving towards the end of its
closed and switch contacts 181 will open to release P.
cylinder communicating with duct it}, will pass into the
R hold circuit will then be broken at p2 and R will re
end of the other cylinder from which the corresponding
lease. Q also will be released at p1. To prevent the
piston is retreating. This arrangement avoids hydraulic
release of R being prejudiced'by the premature closure
transients at the instant of change-over from one drive to
of q2 back contacts, Q is made slow-to-release. All the 40 another because there is no pressure difference across the
relays will now be released and the table 1 will be driven
piston, nor across the tap, of the idling cylinder so long
by the ?rst drive, the second drive being positioned with
as the tap is open and the locking of the foot of this
its foot FII unlocked. The relay contacts will then all
drive causes the piston to move in the same direction as
be in the states shown in FIGURE 2. If, however, in
it will be urged to move by the hydraulic ?uid passed to
the course of the change-over from the ?rst drive to the
it from VI when its tap is closed.
second drive during the period when both feet are locked,
In other respects the operation of the arrangement
the driving signals call for a change of direction of table
shown in FIGURE 4 is the same as that previously de
1, PI will reverse direction towards the centre of its stroke
scribed in relation to FIGURES l, 2 and 3.
and switch contacts 281 will‘ open leaving switch con
In an arrangement similar to that illustrated in FIG
tacts 351 closed. This will release P, and p1 will open 50 URE l, the positioning of the free foot may be con
to release Q and p2 will open to release R. The circuits
trolled electrically rather than by mechanical means such
of FIGURE 2 will now all be restored to the state shown
as the racks 6, ‘7, pinion 5, cradle 4, and piston cylinder
in the ?gure and the ?rst drive will resume the driving
arrangement PIII/ CHI.
This can be achieved by providing auxiliary hydraulic
When table 1 is moving to the left, the change-over is 55 piston and cylinder assemblies connected in parallel with
initiated by the closing of switch contacts 181 and 481
the main driving pistons and cylinders PI/ CI and PII/CII.
but the sequence of operations of the P, Q, and R relays
The energisation of these auxiliary ‘cylinders may be
is as above described for the case where the change-over
controlled by auxiliary switches similar to 18 and 25
is initiated by switch contacts 281 and 351.
(or 33 and 48) but set closer together so that one or
FIGURE 3 shows the foot locking arrangement in 60 other of these is operated when the driving piston has
cross section on an enlarged scale.
The bed on which the foot slides when free, is T
shaped and the lower surfaces of the projecting ?anges
of the bed are engaged by ?anges inwardly projecting
from independent side walls of the foot which embrace
moved but a short way in one direction or the other from
its central position. The action initiated by this auxiliary
switch is such as to drive the idling drive towards the ap
propriate end of its stroke until one of the limit switches
65 18/28, or 38/48 is operated whereupon, if and when the
the ?anges of the bed. The foot F is spaced from the active drive has also operated ‘one of its limit switches
upper surface of the bed and the foot has at least one
‘the change-over action proceeds under control of circuits
cylinder LC recessed into its under side. A locking
such as those illustrated in FIGURE 2. If the driving
plunger L rides in the cylinder LC and the cylinder LC
signals reverse the direction of the active drive before
above plunger L is in communication with a gallery 70 such a changeover is initiated, then the ultimate release of
LG to which hydraulic ?uid under pressure can be admit
the auxiliary switch previously operated by the active drive
ted under control of an electro-magnetically operated
is arranged to cutoff the positioning action of the auxiliary
valve LV (not shown). The valve LV can be operated
cylinder of the idling drive so that it no longer approaches
in one direction to connect LC to the high pressure side
a limit ‘switch. If the driving signals retain this changed
vof the hydraulic pressure supply system whereupon 75 direction the other auxiliary switch will be operated and
the idling drive will be positioned in the opposite direc
tion by its auxiliary cylinder until the other limit switch
is operated. Preferably the positioning action of the
auxiliary cylinder is cut off when the drive which is be
ing positioned operates one of its limit switches. The
drive will then retain the position so attained until the
active drive operates one of its limit switches, to initiate
the change-over as previously described.
Another method of positioning the free foot in an
arrangement similar to that shown in FIGURE 1, is to
apply the servo or command signals in reversed sense to
the valve controlling the corresponding piston/cylinder
to-operate relay WB after a time lag; wbl transfers VAII
(already disconnected from the reversed command sig
nals at 382 or 482) to the command signal source-—
both drives are now working together; wb2 operates slow
to-operate relay WC; wcl breaks the operate circuit of U
but U is still held over r2 front contacts and (13 front
contacts so that U does not release.
Ifmovernent of the slide in response to the command
signals continues in the same direction PII/CII will re
treat from the limit switch (33 or 48‘) to which it was
previously positioned and either 381 or 451 will open to
release Q with R remaining operated over r1 and p2 in the,
?rst instance and later over r1 and q2 (back), the latter
contacts replacing p2 when P releases on the opening of
?ed by the omission of the rack and pinion assembly 4, 5,
6, 7 and of the piston, cylinder, valve and tap assembly 15 181 or 182 soon after the commencement of the position
ing of PI/ CI. ‘In FIGURE 5, W is held operated over r2
PHI, CIII, VIII, Till and TIV. The control circuits also
front contacts but U is released on the opening of q3 since
require to be modi?ed by the substitution of the circuits
its alternative operate path is broken at wcl (WC being
shown in FIGURE 5 for the B, ‘C, D and E portions of
assembly. The arrangement shown in FIGURE 1 is modi
In FIGURE 5, two relays U and W, with associated re 20
lays UA, UB, UC, and WA, WB, WC respectively are re
sponsible for the control of the PI/CI and P-II/CII pis
ton/cylinder assemblies also respectively.
Except during a change-over operation, one of the pair
of relays U and W is operated and the other released.
Each of these relays has two operate paths, one via con~
tacts 1'2 and the other via back contacts of one of the as
operated as previously indicated).
The release of U has the following results‘: ul back
contacts close an alternative holding circuit for TI so that
TI is not opened on the subsequent release of UC: uZ re
leases slow-‘to-release relay UA; ual releases LVI to un
lock foot FI; uaz releases slow-to-release relay UB';
ubl back contacts prepare a circuit from the source of re
versed command signals to VAI. This path is broken at
sociated relays of the other of the pair. The operation of
one of the contacts 182 or 282 and the operated switch
will not be released until the ?rst drive moves off the
open to deny the corresponding operate path to relay U.
such a value that a much attenuated reversed command ‘
conditions obtain r2 back con-tacts are closed to provide an
tioned until the other limit switch is operated whereupon
operated limit switch under the in?uence of the reversed
R is associated with drive by PII/Cil and when these
conditions obtain r2 front contacts are closed to provide 30 command signal. To make this possible each of the con
tacts 182, 282, 382 and 452 is bridged by a resistance of
an operate path for relay W and the r2 back contacts are
signal can pass when the contacts are open. The ?rst
The second operate path for U is broken at the wcl con
drive can then commence a very slow positioning action
tacts of WC one of the relays associated with W. Opera~
tion of W operates WA over W2. WA operates WB over 35 until the opened contacts (182 or 282 as the case may be)
closes to apply the full strength of the ampli?ed reversed
wa2. WB operates WC over wb2. Similarly, non-opera
command signal to VAI which causes PlI/CI to be posi
tion of R is associated with drive by PI/CI and when these
the reversed command signals applied to VAI are again
operate path for relay U and r2 front contacts are open to
deny the corresponding operate path to W whose other op 40 attenuated. The ampli?cation factor and the value of
the resistance are chosen so that the attenuated signal is
erate path is broken at ucl, the relays UA, UB and UC be
not su?icient to damage the piston and cylinder when it
ing operated on operation of U in the same way as are
reaches the end of its stroke. Indeed a' careful choice of
WA, WB and WC on operation of W.
‘these values in relation to the maximum speed of the table
UA, U3 and UC being operated hold Tl operated (tap
closed) over uc2. LVI operated (foot locked) over ual 45 1 can ensure that the drive which is being positioned can
never reach the end of its stroke; ub2 releases UC; ucl re
and VAI connected to the source of command signals at
stores the alternative operate circuit for W; uc2 discon
nects one of the operate paths of TI but the latter remains
During the course of driving operations by PI/CI posi
over M1.
tioning of foot FII has been proceeding my means of the
It will be noted that TI is only opened for a brief
application of command signals of reversed sign to the
interval between the operation of U (breaking ul) and
actuator VAII of valve VII. These signals are prefer
the operation of UC (closing uc2) that is to say during
the successive operate lags ‘of UA,‘ UB and UC. The
same applies to TII mutatis mutandis. During driving
the driving function. When the circuit of FIG. 5 is used
and positioning the taps must be closed and, with this‘
each of the limit switches has two contact sets, one nor
of positioning the idle drive, it is only necessary
mally open (eg. 181 in FIGURE 2A) and one normally
to provide the taps so that the piston of the erstwhile
closed (cg. 182, FIGURE 5) and as soon as FII has been
idling drive is not locked in its cylinder at the instant
positioned to the point at which one of the limit switches
when its foot it locked by operation of UA or WA as
38 or 48 is operated, either 332 or 4-82 switch contacts
the case may be, and before the corresponding‘control
open to disconnect VAII from the source of ampli?ed re 60
valve has been switched to control by the commond sig
versed command signals. This must have the effect of
nals on ‘operation of UB or WB as the case may be.
leaving PII/CII neutralised which may be e?ected by'
v‘With the arrangement of FIGURE 5 the monitoring
spring loading valve VII to a neutral position to which
system control circuits may be arranged as in FIGURE
it will automatically return when VAII is disconnected.
2E, in which case the signals controlling the valve ac
If, now, a change-over operation is initiated, the cir
tuator of the working drive will be the resultant of incom~
cuits of FIGURE 2A cause the operation of P, Q, and R
ing programme signals and monitoring signals from the
(in that order), as previously described in relation to the
monitoring system of that drive and the reversed signals
circuits of FIGURE 2, A, B, C, D and E. Contacts q3
for positioning the foot of the idle drive will be derived
(FIGURE 5 ) join W to the operate circuit of U and when
those resultant signals. It is possible, however, to
r2 contacts change over an instant later there is no break
keep the monitoring system of the idle drive in operation
in this circuit since r2 contact set is of the make-before
by providing individual comparator circuits for the two
break type.
drives and applying the reversed signals for the idle drive
‘W will now operate with the following results: WA is
to its individual comparator the output of which is passed
slow to operate ‘and operates after an interval over W2;
wa1 operates LVII to lock foot =FII; wa2 operates slow 75 to the valve actuator of the idle drive to control position
ably ampli?ed to ensure that foot P11 is positioned suitably
some time before PI-I/CH will be required to take over
ing of its foot. This ensures that the positioning operation
proceeds at a speed governed by the setting of the am
pli?er inserted in the reversed signal circuits without re
gard to the friction or other loads resisting the positioning
or 281; VAl, previously connected to the reversed com
mand signal source over uml back contacts had this path
attenuated at 182 or 282 :by the resistance ‘bridging the
of the idling drive. _
ation. PII/CII now approaches the end of its stroke and
operates one of its limit switches 38 or 45: 381 or 481
In either event, of course, there remains the necessity of
phasing the two monitor systems during a change-over
from one drive to another. This phasing problem may
be solved by locking the feet only at predetermined posi
tions along the length of the ‘bed; for instance by means of
a tapered pin engaging any one of a number of accurately
located holes ‘along the length of the bed. ‘FIGURE 6
shows in detail an arrangement of this type. A foot F,
drawn to an enlarged scale as compared with FIGURE 1,
is provided with a number of cylindrical ‘bores LCr(such
as LC in FIGURE 3), spaced apart along the direction of
opened contact, on completion of the positioning oper
operates Q; ([3 operates U over r2 front and g3 front con
tacts; ul operates UA, n2 and u3 switch UM and UN to
operating circuits via ual and ubl respectively; UA, oper
ated, operates, in delayed succession, UM over ual and
U3 over M2; UN therefore operates over ub2 in similarly
delayed succession after UM; uml front contacts connect
the command signal source to, VAI and unl front contacts
operate LVI to lock foot FI, these actions following one
15 another in timed sequence; the operation’of UN'also oper
ates UC at 1:122 and ac]. back contacts open to break the
movement of the foot when idle. In each of the bores
alternative operate circuit of W but W still holds over r2
LC is a plunger L (corresponding to plunger L in FIGURE
front contacts. Both drives are now operating under con
3). The plungers have an upper cylindrical portion act
trol of the command signal and PI/CI will be moving
ing ‘as a piston, an intermediate accurately ground tapered 20 away from its operated limit switch 18 or 28 which, on
portion ‘and a lower rounded tip. Spaced along the bed
the opening of 181 or 281 contacts, as the case may be,
is a series of holes LH tapered to engage accurately the
results in the release of P followed by the release of Q
tapered intermediate portions of the plungers L. The
and R. This causes W to be released (r2, and q2 front
pitch of the holes LH differs from that of the plungers L
contacts both being now open).
and in FIGURE 5 the former is smaller than the latter.
On the release of W, the following events take place:
A number of plungers L are provided to enable the spac
WA is released by the breaking of WI, whereupon (after
ing apart of discreet positions in which a foot can be
the release lag of WA) wal releases WN (Whose operate
locked to be kept small without the necessity of having
path was changed over from that via wbl on the release
an inordinately large number of closely spaced holes along
the bed. The difference in pitch between plungers L and ‘
holes LH ensures that one of the former will be close to
' a hole at the instant when locking is- required and the
rounded tip of that plunger will cause it to pull the foot
along till the plunger in question is lined up with the
nearest hole which it will enter to locate the foot ac
of W2; waZ releases WB, whereupon, (after the release lag
.of WB) wbl releases WM (whose operate path was
changed over from that via wal on the release of W3).
It will be seen that WN and WM release in delayed suc
cession in that order. By comparison with the description
above the operation of the corresponding relays UM and
UN, it will be seen that the order of release of these relays
curately by engagement of its intermediate tapered section
in the tapered bore of the hole.
is the opposite of their order of operation. The result of
the release of these relays in that order is that the foot of
The plungers L are all connected to the same hylraulic
the drive about to relinquish the driving function is re
leased and then, in timed succession thereafter, this drive
is removed (at wml) from the control of the command
?uid gallery LG and each is urged away from the bed by
a tension spring. The plungers other than the one which
is near enough to a hole to enter it, will be forced down
upon the top surface of the bed When the lock valve LV
operates but the pressure need not be great as the locking
of the foot is ensured by the direct mechanical engage
ment of a plunger in one of the holes. Thus the pressure
of the tips of the said other plungers upon the surface of
the bed will not be such as to resist the pulling-in action
of the plunger which engages a hole to any signi?cant
With this arrangement the provision of the taps TI and »
T11 and the circuits a1, 1102 and W1, wcZ which open the
taps only during the time when a foot is actually being
locked, are essential in order that the operative one of the
plungers L may be free to draw the foot to the nearest
discreet locking position without any resistance from the
piston and cylinder of the drive in question. With the
locking arrangement of FIGURE 3 however, it is pos
sible to omit the taps TI and T11 provided that somewhat
modi?ed control circuits are used.
FIGURE 7 shows such circuits. In FIGURE 7 relays
and their contacts having corresponding ‘functions are
given the same designations as in FIGURE 5.
Suppose that PII/CII is driving: R is operated holding
W operated at r2 front contacts; WA is operated at W1;
W2 and w3 front contacts switch WM and WN to the
operate paths via wal and wbl respectively; WA holds
WB operated at wa2 and WM operated at wal via w2
front contacts; wbl ‘holds WN operated over w3 front
contacts; WM, operated, connects the command signal
source to VAII at wml; WN, operated, holds ‘foot FII
locked by means of LVII energised over wnl, and W112
holds WC operated; wcl breaks the alternative operate‘
circuit of U which is unoperated because r2 back contacts
are also open; PI/CI is positioned and has operated one
of its limit switches 18 or 28 holding P operated over 181
signals and a path prepared for positioning control by the
reversed command signals. This path is completed via
one of the contacts 382 or 452 which is closed and via
the resistance bridging the other of them which is open.
The reversed command signals will therefore be applied
in attenuated form to VAII and PII/CII Will start the
positioning process at slow speed until that one of the
contacts 382 or 482 which is opened, is closed on the sec
ond drive moving off the operated limit switch, where
upon the reversed command signals are applied in ampli
?ed form and the positioning process is accelerated. When
the second drive is fully positioned one of the limit
switches 38 or 48 again operates to attenuate the reversed
command signals again. The idle drive will then move
I slowly towards the end of its stroke, over running the
operated limit switch. As already indicated in relation
to FIGUE 6, it is of no consequence if this decelerated
position action causes the idle drive to reach the end of
its stroke but this may be avoided by suitable choice of
the amplification factor ‘applied to the reversed command
signals, the switch contact bridging resistances, the release
lags of the various relays culminating in the release of
WM (or UM when PI/CI is idling). The valves used
for V1 and VII must be of the type such that a given
setting produces a given piston velocity, independent of
the load on the drive controlled by the valve, since this
velocity must not vary on the occurrence of variations in
say the cutting load (where the invention is applied to a
machine tool). Therefore the magniture of the reversed
command signals will similarly govern the positioning
velocity. The positioning action of one drive commences
after the commencement of the driving action of the
other drive since it is delayed during the successive re
lease of W, WA, WB and WM (or U, UA, UB and
I UM). It will therefore be required to catch up the active
drive. It starts slowly; the attenuated reversed signals
may be of the order of .5 of the amplitude of the com
mand signals. When the limit switch is released the posi
tioning action must be accelerated to enable positioning to
be ‘completed before the active drive reaches the end of
its stroke. The ampli?ed reversed command signals,
when no longer attenuated, may then have an amplitude
of the order of 1.2 times the amplitude of the command
signals. If during this period the command signals re
verse direction the reversed command signals will do like
wise and the positioning direction will be reversed. The
positions of the limit switches also effects the positioning
operation but the principal factor governing the placing
said drives may operate in turn to produce relative move
ment between said ?rst object and said second object.
2. Apparatus as claimed in claim 1 in which said means
for actuating said positioning means of said second drive
is under control of said indicating means of both of said
3. Apparatus as claimed in claim 1 in which said posi
tioning means of each of said drives comprises a releas
able mechanical coupling between the two said drives
arranged so that relative movement in one direction be
tween the two said members of that one of said drives
which is for the time being executing a driving action,
gives rise to relative movement in the opposite direction
between the two said members of that one of said drives
of the limit switches is the necessity to ensure that the
drive about to relinquish the driving function does not 15 which is for the time being not executing a driving ac
reach the end of its stroke during the change-over oper
4. Apparatus as claimed in claim 3 in which said
ation in the brief period when both drives are working
mechanical coupling acting as said positioning means
together with both feet locked, under control of the com
comprises two racks only secured to said second member
mand signal.
It is understood that the use of separate short range 20 of each of said drives and extending inwardly therefrom
in overlapping spaced relation, a pinion engaging each
monitoring assemblies for the two driving mechanisms is
not fundamental to the invention. There are methods
available for avoiding the use of diifraction gratings or
rack and supported between said racks upon an axle car
provision of a device as long as the range of movement
and cylinder assembly carrying respectively two parts of
between the two objects, presents less di?iculty. Such
devices may be used in conjunction with the present in
said piston and cylinder assembly, said valve being ar
ried by one member of an hydraulic piston and cylinder
assembly the other member of which is secured to said
equivalent position monitoring devices having extremely
?ne rulings or equivalent registration marks whereby the 25 ?rst object, said two members of said hydraulic piston
vention, enabling the phasing arrangements hereinbefore
described in relation to FIG. 2E to be dispensed with.
We claim:
1. Driving apparatus for causing relative movement
along a predetermined pathvbetween a ?rst object and a
second object, comprising a ?rst drive and a second drive,
a hydraulic valve controlling the ?ow of hydraulic ?uid to
ranged so as to maintain said piston and said cylinder of
said assembly in predetermined relative positions, means
for removing said assembly from control by said valve
and rendering said piston and said cylinder free to make
unhindered relative movements whereby said positioning
means may be disabled.
5. Apparatus as claimed in claim 1 in which said posi
said drives being driving mechanisms and each said drive 35
tioning means of each of said drives comprises means
in turn comprising two members between which relative
for applying to said actuating means a signal correspond
movement takes place to provide the driving action of said
drive, the ?rst of said members being secured to said ?rst
object and the second of said members being provided
with locking means, said locking means being means for
releasably securing said second member to said second
object at various positions along a track parallel to said
predetermined path, actuating means, said actuating
ing to said incoming signal but of reversed sense so that
while said incoming driving signal is operating said ac
tuating means of one of said drives to cause relative
movement between said two members of said drive in one
direction to provide a driving action, said correspond
ing signal of reverse sense operates said actuating means
of the other said drive to cause relative movement between
means adapted in response to an incoming driving signal
to initiate driving action on the part of said drives, posi 45 its two said members in the opposite direction.
16. Apparatus as claimed in claim 5 in which said cor
tioning means, said positioning means being adapted for
responding signal of reverse sense is ampli?ed to ac
positioning said ?rst member of each said drive relative
celerate the positioning of said drive which is not ex-,
to said second member of each said drive when the drive
ecuting a driving action as compared with the velocity of
in question is not executing a driving action, and indicat
relative movement between the two said members of the
ing means, said indicating means being adapted for indi
other said drive which is executing a driving action.
cating the relative positions of said two members of each
7. Apparatus as claimed in claim 6 with means under
said drive at least at a plurality of predetermined relative
control of said indicating means of the said drive which
positions of said two members, the apparatus further
is being positioned for arresting the positioning action
comprising means for operating said locking means of
said ?rst drive and for releasing said locking means of 55 when the two said members of said drive have reached
said second drive, means for applying driving signals to
said actuating means of said ?rst drive, means for ac
predetermined relative positions.
8. .Apparatus as claimed in claim 6 with means under
control of said indicating means of a said drive which
tuating said positioning means of said second drive to
is being positioned for severely attenuating said corre
place members of said second drive in predetermined rela
sponding signal of reverse sense when the two said mem
tive positions, means under control of said indicating 60 bers of said drive have reached predetermined relative
means of said ?rst drive for operating said locking means
of said second drive and bringing said actuating means
9. Apparatus as claimed in claim 1 in which the var
of said second drive under control of said driving signals
ious means further comprised in said apparatus are ar
and means, operable when said locking means of both
ranged, when said indicating means of both said drives
said drives are operated and before either of said drives 65 have operated to produce a sequence of events in the
has reached an end of its range of driving action, for re
following order, ?rst, said positioning means of said sec
leasing said locking means of that one of the two said
ond drive is disabled whereby the two said members of
drives which is nearest to an end of its driving range when
it is at that instant approaching in the course of its driv
ing action and removing said actuating means of that said
drive from the control of said driving signals, said ?rst
drive and said second drive being interchangeable in re
spect of the functions of the various means further com
said second drive are free to execute unimpeded relative
movements, secondly, said locking means of said second
drive is operated to secure said second member of said
second drive to said second object, thirdly, said actuat
ing means of said second drive is brought under control
of said driving signals so that both said drives are ex
prised in said apparatus as aforesaid whereby the two 75 ecuting mutually assisting ‘driving action, fourthly, said
locking means of that one of said two drives which is
nearest to the, end of its driving range to which‘ it is
one of a series of depressions at predetermined positions
along said track of said second object.
at that instant approaching is released, ?fthly, said actuat
14. Apparatus as claimed in claim 13 in which said
ing means of said drive last above referred to is removed
from control by said driving signals, and sixth, said posi- '
tioning means of said drive last above referred to is op
erated to cause relative movement of said two members
‘depressions are equally spaced along said track and in
which each said locking means comprises a plurality of
detents spaced apart along the direction of said track
with a spacing which dilfers from the spacing between
of that drive in the direction of opposite end of their
adjacent depressions in said track.
driving range.
15. Apparatus as claimed in claim 1 in which each
10. Apparatus as claimed in claim 1 in which there 10 of said drives takes the form of an hydraulic piston and
is associated with each of said drives a motion monitoring
cylinder assembly, in which said actuating means is an
device so ‘arranged as to monitor relative movements be
electro mechanical transducer arranged to operate an
tween said ?rst member and said second member of said
hydraulic valve ‘controlling the supply of pressurized hy
drive, the apparatus comprising a feedback servo control
draulic ?uid to said piston and cylinder assembly.
system adapted to compare an incoming command signal 15
16. Apparatus as claimed in claim 15 in which each
with a signal from said monitoring device associated with
hydraulic piston and cylinder arrangement is provided
that one of said drives which is executing a driving action
with a by-pass tap‘ which, when opened, permits rela
and from such comparison to derive a difference signal,
tive movement between said piston and said cylinder
such di?erence signal constituting said driving signal to
unhindered by the presence of hydraulic ?uid within said
which said actuating means of that said drive is respon
’ 17. Apparatus as claimed in claim 16 in which a single
11. Apparatus as claimed in claim 10 with means for
changing over ‘from one of said monitoring devices to
the other for comparison of its outward signal with the
incoming command signal, such changeover taking place
valve controlled by a single electro mechanical transducer
controls the two said piston and cylinder assemblies, said
piston and cylinder assembly being connected in series
at a time when said locking means of both said drives
are operated to secure said second members of both said
drives to said second objects.
12. Apparatus as claimed in claim 10 with means for
bringing said signals of both said monitoring devices into
synchronism before changing over from one to the other
as aforesaid.
13. Apparatus as claimed in claim 11 in which said
locking means of each said drive comprises at least one
detent ‘coupled to said second member of said drive'and 35
adapted to be moved into or out of engagement with any
in the hydraulic ?ow circuit, each piston and cylinder
assembly being removable from control of said single
valve by the opening of its associated said bypass tap.,
‘References Cited in the ?le of this patent
, 2,311,142
Turretini ____________ __ Feb. 16, 1943
Gepfert _____________ __ May 25, 1954
Wagner _____________ __ Nov. ‘16, 1954
' Italy _______________ __ Feb. 23, 1945
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