US3424059A - Linear hydraulic motors - Google Patents

Description

Filed April 11, 1967 Jan. 2 s, 1969 a; CONNER ET AL 3,424,059

LINEAR HYDRAULIC MOTORS Sheet of 4 07-2 /3 I 9,752 F 4 I l lnvenlou c.I.CONA/ER 81/. Hon/4RD 1).)? WALKE & 9- W001 y M m... r fix Jan. 28, 1969 c, N R ET AL 3,424,059

' LINEAR HYDRAULIC MOTORS Filed April 11, 1967 Sheet 2 of 4 nvenloli torneys 1 c. 1. CONNER ET AL I 3,424,059

LINEAR HYDRAULIC MOTORS Filed April 11, 1967' Sheet 3 of 4 A16+C0LA +a00 w 0 +90 0 190 0 +90 0 -90, 0

,CZLCQA/A/ER BIZ/5 D. E MLKER 6 4 W ve lorneys Jan. 28, I969 c. CONNER ET L 3,424,059

LINEAR HYDRAULIC MOTORS Filed April 11, 1967 Sheet P of 4 WWW; W 1 l H 1' lnvenlor; C. I. Cow/v51? B.V.HOWARD 0. FT Wm. KER 624M 2;

United States Patent 0 3,424,059 LINEAR HYDRAULIC MOTORS Charles Irvine Conner, Penicuik, Midlothian, Bernard Victor Howard, Currie, Midlothian, Donald Ferguson Walker, Barnton, Edinburgh, and Godfrey Allen Wood, Eskbank, Dalkeith, Scotland, assignors to Ferranti, Limited, Hollinwood, Lancashire, England, a company of Great Britain and Northern Ireland Filed Apr. 11, 1967, Ser. No. 630,016 Claims priority, application Great Britain, Apr. 12, 1966,

15,838/ 66 U.S. Cl. 91176 6 Claims Int. Cl. F01b 15/00; F011 15/08 ABSTRACT OF THE DISCLOSURE This invention relates to linear hydraulic motors of the typehereinafter referred to as the type stated which includes a stator and a translator mounted for straight-line movement relative to one another, the stator having a cyclic edge profile extending in the direction of movement and the translator having at least four cylinders disposed normal to that direction and containing hardened metal balls urged by the actuating fluid to engage the stator profile at fractional wave-length spacings along it, thereby causing the movement. In general, the stator may have for each of in complete cycles of the profile 2n cylinders (where n is greater than unity) spaced at rz-wavelength intervals over the cycle. The total number of cylinders is thus Zmn.

Unless otherwise stated it will be assumed that the stator is the fixed and the translator the moving component of the motor, but the terms stator and translator should be understood as including an arrangement in which the fixed component is the translator, the stator moving along it.

It is usual in such motors for the fluid to be applied to the cylinders under both a servo and a cylinder-sequence form of control.

In obedience to some kind of signal, such as an error signal, the servo system controls by means of a two-way valve the connection between two channels from the source of fluid under pressure to two intermediate channels leading to the translator, the two from the source performing supply and exhaust functions respectively. The controlling signal is usually electrical but may be hydraulic.

The valve connects the supply channel to one or other of the intermediate channels in dependence on the sense of the movement required, or on the sense of the thrust where the servo valve is actuated to provide a thrust in the reverse direction to the actual movement in order to arrest it, the sense in each case being represented by the sense or other characteristic of the signal, and connects the other intermediate channel to the exhaust channel.

The connection of the intermediate channels to the cylinders of the translator is exercised by the cylindersequence control in dependence solely on the position of the translator relative to the cycles of the stator profile. The apparatus for this purpose normally takes the form of a porting block which in every position of the translator couples the intermediate channels to the cylinders in such manner that a pressure diiference between the iluids in those channels is ettective in moving the transator.

The porting block thus acts as a kind of distributor and usually takes the form of a porting blade rotating in a cylinder having ports connected to the intermediate channels and to the cylinders of the translator. As the porting blade is controlled solely by the translator movement, independently of the servo signal, it is usually driven by a rack and pinion of which the pinion is coupled to the blade and the rack is disposed alongside the stator, to which the rack is secured, over the full linear range of movement of the translator.

An object of the present invention is to provide a new and useful motor of the type stated, a particular object being to provide such a motor in which the cylindersequence control is effected by means not including a rack and pinion arrangement as described.

In accordance with the present invention there is provided a linear hydraulic motor of the type which includes a stator and a translator mounted for straightline movement relative to one another, the stator having having a cyclic edge profile extending in the direction of movement and the translator having for each of m cycles of the stator profile 2n cylinders disposed normal to that direction and containing hardened metal balls urged by the actuating fluid to engage the stator profile at 11 wavelength spacings along the profile, where n is greater than unity, the motor also including changeover means reversibly connecting a supply channel and an exhaust chanel of actuatig fluid to two intermediate channels in dependence on a control signal, 11 porting devices each for reversibly connecting the two intermediate channels to two groups each of m cylinders associated with only that device, the cylinders in each of the two groups associated with that device being at in-phase spacings of the profile and the cylinders of one of those two groups being at counterphase spacings from those of the other group, and porting-control arrangements for abruptly actuating the porting devices sequentially at respective positions of the translator along the stator profile at n wavelength spacings of the profile so as to render a pressure difference between the fluids in the intermediate channels effective in moving the translator in a direction dependent on the sense of that differece.

In the accompanying drawings:

FIGURE 1 is a diagram partly in section and partly in schematic form of a linear hydraulic motor in accordance with one embodiment of the invention,

FIGURE 2 is a set of waveforms to illustrate the operation of the motor of FIGURE 1,

FIGURE 3 shows in detail a part shown generally in FIGURE 1,

FIGURES 4 and 5 show parts of the motor of FIGURE 1 modified in accordance with two further embodiments,

FIGURES 6 and 7 show modified forms of the motor of FIGURE 1 in accordance with two further embodiments, and

FIGURE 8 is a set of waveforms to illustrate the operation of the motor of FIGURE 7.

An embodiment of the invention will be described by way of example where the motor has four cylinders for each of two cycles of the profile. Thus 11:2 and m=2.

In carrying out the invention in accordance with this form, a linear hydraulic motor includes a fixed stator 11-see FIG. 1having a cyclic edge profile 12 and arranged to be traversed by a translator 13 along the straight line of axis 14. Profile 12 is in two complementary parts,

an upper and a lower as seen in the drawing, which face one another across axis 14. Each profile is of ribbon-like form as if generated by a movement of the curved line 12 of the diagram normal to the plane of the paper for a short distance.

The translator has eight cylinders A to D and A to D disposed with their axes normal to axis 14 at quadrature that is, quarter-wavelength-spacings along the profile 12. The cylinders are arranged alternately in two rows displaced from one another in a directional normal to the plane of the paper. Thus cylinders A, C, A, C, form one set at counterphase spacings with their axes coplanar in the plane of the paper, and B, D, B, D, a second counterphase set behind them (as seen in the diagram). This second set is therefore concealed to some extent by the first set. The staggering of the cylinders in this way allows them to have a larger diameter than if they were all in line with their axes all coplanar.

Each cylinder contains two hard metal balls A1, A2, B1, B2 and so on. They are urged apart to engage the respective parts of the stator profile by the actuating fluid, which is admitted to the cylinders by way of ports which are not shown.

For controlling the admission of the actuating fluid to the cylinders, the motor includes a servo control in the form of changeover means 21 for reversibly connecting a fluid supply channel Fs and an exhaust channel Fe to two intermediate channels I1 and I2 in dependence on an electrical control signal applied over a lead 22. Channels Fs and Fe are in the form of high pressure pipes running respectively from the source (not shown) of the actuating fluid and to a convenient exhaust point. Changeover means 21 takes the form of an electrically-operated hydraulic valve, of which various known kinds are available.

The cylinder-sequence control is exercised by two porting devices P1 and P2 in the form of hydraulic spools. Spool P1 is associated with cylinder set A, C, A, C, and is arranged to connect channels 11 and I2 reversibly to the constituent groups AA and CC. The cylinders in each group are thus at in-phase spacings, whilst the cylinders of one group are at counterphase spacings from those of the other group of the set.

To provide this reversal control, the connections from the spool to the cylinders are by way of high-pressure pipes or channels AA and CC to the corresponding groups of cylinders. The spool has two operative positions. In one of them it connects channel I1 to group AA and channel 12 to group CC. In the other, these connections are reversed, so that channel I1 and I2 are connected to groups CC and AA respectively. Details of a suitable spool are described below with reference to FIG. 3.

Spool P2 is similarly arranged to connect channels I1 and I2 reversibly to cylinder pairs BB and DD.

Valve 21 is actually carried by a part 23 of the translator, and the spools in another part 24 termed the porting block. The pipe channels between the valve and the spools and between them and the cylinders are also carried by the translator. For convenience, however, the valve, the spools, and the pipes are depicted to an enlarged scale as if detached from the translator.

The actuation of each spool from the one to the other of its operative positions is effected by porting control arrangements. These may take various forms in accordance with the invention. In the embodiment of FIG. 1 it is assumed that the movement of the worktable (or other object controlled by the motor of the invention) is measured by an optical fringe-counting method that includes an illuminated optical grating 25 long enough to extend over the full range of the translator movement. For deriving that measurement, there is provided photoelectric equipment which includes a bank of photocells and associated electrical circuits. As the present invention is not concerned with this equipment, apart from grating 25, it is omitted from the drawing.

To provide the porting control, the translator carries a photocell 26 which traverses grating 25 as the translator traverses the stator. As the grating is so ruled as to form a pattern of alternate light and dark bands normal to the direction of movement, the signal derived by the cell has a square waveform. In a stage 27 (which, like photocell 26, may be carried by the translator) this signal is frequency-divided to produce two switching square wave signals S1 and S2 in quadrature with one another at the frequency at which the stator profile is traversed. Stage 27 includes the usual array of binary counter circuits such that the count-down ratio is equal to the ratio of the wavelength of the stator edge profile to that of the grating pattern. To actuate the spools, signals S1 and S2 are ap- :plied to solenoid relays R1 and R2 which control the piston members of the respective spools, moving the spools in one direction or the other in dependence on the positive or negative sense of the signals.

The movement of the translator is effected by the pressure exerted by the cylinder balls on the sloping parts of the stator profile. With the translator in the position depicted, for example, it is clear that cylinders of set A, C, A and C are inoperative, whatever the pressure of the fluid in them, because the balls in them engage the troughs or crests of the profilethat is, the parts of the profile that are parallel to axis 14.

On the other hand, as the cylinders of set B, D, B, and D are in alignment with sloping parts of the profile the pressure in them tends to cause movement of the translator along its axis. Whether this movement is to the right or to the left (as viewed on the drawing) depends on whether the pressure in cylinders of group BB is greater or less than that in group DD, the movement being to the left or to the right, as the case may be.

For a continuous movement in one direction, it is necessary to reverse these pressure differentials each time the cylinders concerned cross the troughs or crests of the profile. Thus after a movement of the translator to the right for a quarter wavelength of the profile from the position depicted, due to the pressure in the cylinders of group DD being greater than that in cylinders of group BB, the pressure in cylinders BB must become the greater if the rightwards movement is to be continued. As the respective sets of cylinders are at quarter-wavelength spacings from one another, these reverses of pressure differentials must take place at a similar spacingthat is, in quadrature.

This control of the pressure differentials is exercised by the spools P1 and P2, each of which is itself controlled by signal S1 or S2, as the case may be, to change over the connections from intermediate channels I1 and 12 to the set of cylinders associated with the spool every half-wavelength of the translator movement.

Thus, assuming that the pressure in channel I1 is greater than that in channel I2, a movement of the translator to the right from the position depicted in FIG. 1 may be as illustrated by the waveforms of FIG. 2.

S1 and S2 are the waveforms of the controlling signal from stage 27, each as a voltage alternately positive and negative plotted against time.

Waveforms A to D illustrate the relative pressures of the fluid in the respective cylinders; above the central horizontal line represents the higher pressure of the fluid in the channel I1 and below it the lower pressure of the fluid in channel 12.

At the time t signal S1 is changing over from negative to positive and so actuating spool P1 to switch channel I1 from cylinders AA to cylinders CC The pressures in these cylinders is therefore changing from high to low, and low to high, respectively.

Also at time t signal S2 is maintaining channel I1 connected to cylinders DD and channel 12 to BB Hence at the time t the drive is being provided by cylinders DD which are about to be assisted by cylinders CC By the time t the translator has moved a quarter wavelength of the pattern to the right from the position shown in FIG. 2. At this moment, whilst the drive is being effected by cylinders CC alone, spool P2 is changing the higher pressure from cylinders DD to BB which at this moment are engaging troughs and crests of the profile. Similarly with the rest of the movement.

As signals S1 and S2 are in quadrature, they ensure the required quadrature relationship between these changeovers of the spools.

The direction of movement is not controlled by the porting system but by the servo system, through the actuation of valve 21 by the signal applied over lead 22. The position of the valve decides which of the intermediate channels is connected to the supply channel Pr and which to the exhaust channel Fe, and in consequence which of the intermediate channels has the fluid at the greater pressure.

Each porting spool is the hydraulic equivalent of an electrical double-pole changeover switch. A suitable arrangement, taking spool P2 as an example, is shown in FIG. 3.

A cylinder 30 contains two piston valves 31 and 32 carried on a common piston rod 33 actuated by solenoid R2 under the control of signal S2. The entry ports for channels 11 and 12 are aligned with the centres of valves 31 and 32 (respectively) when rod 33 is in its mid position, which it in fact never occupies except momentarily when changing from one of its operative positions to the other. An exit port for the common channel BB leading to that group of cylinders is provided at each end of the cylinder. A single exit port for the common channel leading to cylinders D and D occupies a central position in the cylinder.

When the piston is in its operative position at the lefthand end of its stroke, as viewed in the drawing, channel I2 is connected to channel DD and channel I1 to channel BB (by way of the right hand exit port); with the piston at the right-hand end of its stroke those connections are reversed. The changeover switching action is rendered abrupt by the steep-edged waveform of the signal controlling the solenoid.

This comparatively abrupt action of the spools in a porting system in accordance with the invention has the advantage of allowing the pressure-difference changeover to take place when the translator cylinders are closely in alignment with troughs or crests of the profile and hence when there is very little fluid flow into or out of them. The effect of this is to reduce the risk of undesired pressure transients due to the changeover action. This advantage can be enhanced by providing the profile with dwell p0rtionsthat is, by providing in the region of each trough and crest a short linear (straight) portion parallel to the axis of translation.

Where such dwell portions are provided, it is desirable to provide corresponding straight portions in alignment with the other cylinders-that is, the cylinders not aligned with a trough or crest-so as to maintain constancy of thrust.

The positions of such straight portions or flats may be as shown in FIG. 4, which reproduces a cycle of the profile to an enlarged scale and with the amplitude much exaggerated. The flats 35 at trough and crest must merge smoothly into the curves, to which the flats should in effect be tangents. The other flats are shown at 36. The length of each as projected on axis 14that is, in the direction of movementis equal to the length of a flat 35. With the translator in the position shown in FIG. 1, cylinders A and C are engaging flats 35 (not shown in FIG. 1) whilst B and D are engaging flats 36 (also not shown). Thus the balance of the thrusts from B and D is constant whilst A and C are traversing flats 35 and not themselves exerting any thrust.

A porting system under the control of an optical grating, as just described, is only practicable where the pitch of the stator profile is an even multiple of the grating pitch. Where that condition does not obtain, and also where the tool or other object controlled by the motor is not provided with a fringe counter measuring system and it is not desired to provide a grating for the porting control alone, that control may alternatively be exercised from the stator profile by means of cam followers, as shown in FIG. 5.

The pistons of the porting spools P1 and P2 are here spring loaded to one of their operative positions and arranged to be displaced to the other by the fluid under pressure in channel Fs under the control of cam-follower units C1 and C2 respectively.

Taking spool P1 as an example, the associated camfollower unit C1 includes a cam roller 41 carried at the free end of a hydraulic plunger 42 operating in a cylinder 43 and spring-biased to maintain the roller 41 in engagement with the stator profile 12. The fluid under pressure from channel Fs is applied by way of a flow resistor 44 to a port 45 in cylinder 43 part way along the stroke of the plunger and to the end of spool P1 remote from the biasing spring 46. The end of the cylinder 43 remote from the plunger 42 and the spring biased end of spool P1 are connected to the exhaust channel Fe.

In order to prevent the fluid which actuates the spool from reaching the channels between valve 21 and the translator, spool P1 is arranged somewhat differently from its counterpart P1 of FIG. 1. One of the two intermediate channels-I1 as depictedis brought to an entry port at the centre of the stroke, whereas the otherI2 is brought to entry ports at each end. The moving part of the spool in'cludes ,piston valves 47 (at the end of the spool remote from spring 46) and 48, with a third piston valve 49 between them on the same piston rod. Channels AA and CC are fed from only one exit port each. The position of valve 49 on one or other side of the entry port for channel I1 determines whether that channel is connected to channel AA or CC, the remaining connection being by the other two valves. In all positions of valve 47 to 49, valve 47 maintains the actuating fluid isolated from the rest of the spool.

In operation, so long as plunger 42 is not covering the port 45, the fluid from restrictor 44 exhausts through cylinder 43 to channel Fe and insufficient pressure is built up to overcome the force of spring 46 and switch the spool to its other operative position. As soon as the stator profile has driven plunger 42 sufficiently into its cylinder to close port 45, the pressure in the channel between restrictor 44 and the spool becomes sufficient to actuate the spool abruptly to its other operative position against the force of spring 46. The spool is shown so actuated in the drawing, with valve 49 causing channel I1 to be connected to channels AA and valve 48 freeing the adjacent entry port of channel I2 to connect it to channels CC. The spring 46 is fully compressed, and valve 47 keeps the actuating fluid isolated.

Plunger 42 and port 45 in cylinder 43 together with the channels from the supply and to the spool, may accordingly be described as switching means whereby the movement of the cam-follower effects the porting action.

Similar arrangements are provided for spool P2 the components corresponding to components 41 to 49 just described being given the references 51 to 59. Here the spool is shown in its unactuated condition, with the centre valve 59 connecting channel I1 to channels DD and valve 57 freeing the adjacent entry port of channel 12 as well as serving to isolate the actuating fluid.

The required quadrature actuation of the spools is obtained by arranging for the cam rollers 41 and 51 to engage parts of the stator profile at a quarter wavelength spacing.

The switching means may alternatively take an electrical form (not shown) the movement of the cam followers causing the closure or opening of electrical switches in the circuits of solenoids which operate the spools as in the arrangement of FIG. 1.

Where cylinders are provided for a third cycle of the profile, so that 111:3, each of the groups of cylinders controlled by the porting devices is expanded to include a third cylinder. Thus, as shown in FIG. 6, group AA becomes AAA", and so on, The apparatus and its operation are otherwise as before. Similarly where m is more than 3.

Where it is increased beyond 2, the number of porting devices is increased correspondingly, each spool being arranged to connect the two intermediate channels 11 and I2 reversibly to two groups of cylinders. Thus, as shown in FIG. 7, where 11:3, so that there are 6 cylindersA to F, sayper cycle, a third porting spool P3 is added. Assuming that 111:2, one spoolP1, saycontrols counterphase groups AA and DD; spool P2 controls groups BB and EE with a lag of 60 on the groups controlled by spool P1; and spool P3 controls groups CC and FF. It is now necessary to derive a third signal S3 to control the additional spool P3. As shown in FIG. 8, the three signals are now at 60 spacings from one another, as opposed to the quadrature spacings of the two signals of the previously described embodiments, and stage 27 is modified accordingly. Each spool remains as before the equivalent of an electrical double-pole changeover switch. Where the profile is provided with flats, only those at trough and crest are required, as each pair of cylinders between the pair at trough and crest will be exerting a constant thrust between them over the short distance concerned.

What we claim is:

1. A linear hydraulic motor of the type which includes a stator and a translator mounted for straight-line movement relative to one another, the stator having a cyclic edge profile extending in the direction of movement and the translator having for each of in cycles of the stator profile 2n cylinders disposed normal to that direction and containing hardened metal balls urgable by the actuating fluid in the cylinders to engage the stator profile at /212 wavelength spacings of the profile, n being greater than unity, the motor also including changeover means reversibly connecting a supply channel and an exhaust channel of actuating fluid to two intermediate channels in dependence on a control signal, It porting devices each for reversibly connecting the two intermediate channels to two groups each of m cylinders associated with only that device, the cylinders in each of the two groups associated with that device being at in-phase spacings of the profile with respect to one another and the cylinders of one of those two groups being at counterphase spacings from those of the other group, and porting-control arrangements for abruptly actuating the porting devices sequentially at respective positions of the translator along the stator profile at l/n wavelength spacings of the profile r so as to render a pressure dilference between the fluids in the intermediate channels effective in moving the trans lator in a direction dependent on the sense of that difference.

2. A motor as claimed in claim 1 wherein the portingcontrol arrangements include an optical grating fixed with respect to the stator and ruled with lines normal to the direction of movement of the translator, a photo-electric transducer secured to the translator so as to traverse the grating as the translator traverses the stator, an electrical stage for deriving from the transducer output 11 squarewave signals in /2/1 wavelength phase relationship with one another at the frequency with which the translator traverses the stator edge profile, and connections for applying those it signals to actuate the n porting devices respectively.

3. A motor as claimed in claim 1 wherein the portingcontrol arrangements include 11 cam-follower units the cam followers of which are arranged to engage the stator edge profile at V2 wavelength spacings, and switching means whereby the movements of the cam followers effect the actuation of the respective porting devices.

4. A motor as claimed in claim 1 wherein the portingcontrol arrangements are such that each porting device reverses the connections from the intermediate channels to the two groups of cylinders associated with that device when those cylinders are in alignment with parts of the stator profile that are approximately parallel to said direction of movement.

5. A motor as claimed in claim 4 wherein the stator profile is provided with a short straight portion parallel to said direction of movement in the region of said parts of the profile, and with corresponding straight portions with which the other cylinders are then aligned, thereby maintaining constancy of thrust whilst the connections to the said two groups of cylinders are being reversed as aforesaid.

6. A linear hydraulic motor of the type which includes a stator and a translator mounted for straight-line movement relative to one another, the stator having a cyclic edge profile extending in the direction of movement and the translator having two sets of four cylinders per set disposed normal to that direction and containing hardened metal balls urgable by the actuating fluid in the cylinders to engage the stator profile at wavelength spacings along the profile, the motor also including changeover means reversibly connecting a supply channel and an exhaust channel of actuating fluid to two intermediate channels in dependence on a control signal, two porting devices each for reversibly connecting the two intermediate channels to two groups each of two cylinders associated with only that device, the two cylinders in each of the two groups associated with that device being at in-phase spacings of the "profile with respect to one another and the two cylinders of one of those two groups being at counterphase spacings from those of the other group, and porting-control arrangements for abruptly actuating the porting devices sequentially at positions of the translator along the stator profile at /2 wavelength spacings of the profile so as to render a pressure difference between the fluids in the intermediate channels effective in moving the translator in a direction dependent on the sense of that difference.

References Cited UNITED STATES PATENTS 2,619,076 11/1952 Agin 91-275 2,803,110 8/1957 Chittenden 9l275 3,029,792 4/1962 Rasmussen 91-176 FOREIGN PATENTS 961,339 6/1964 Great Britain.

PAUL E. MASLOUSKY, Primary Examiner.

US. Cl. X.R.

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