GB2092229A - Fluid Actuated Positioning Device - Google Patents

Abstract

The invention relates to a pressure-fluid operated positioning device comprising a cylinder, and a piston movable therein between stops within the cylinder itself, at least one of the stops (e.g. 10, 15, 19) being movable from outside the cylinder, preferably through the cylinder wall. The invention also comprises a positioning system wherein at least two pistons operating in one or more cylinders are arranged mechanically in series, and the movement derived therefrom is in the form of increments acting on an object to be positioned in the same direction. <IMAGE>

Description

SPECIFICATION Pressure-fluid Operated Actuating and Positioning Devices and Systems This invention relates to pressure-fluid operated positioning devices and systems. Such devices and systems may operate on an analogue or a digital basis, and the invention is concerned with the latter, that is to say, where movement is imparted to an object to be positioned in one or more finite steps.

An aim of the invention is to provide a construction in which it is possible to use compression type seals, preferably of the ordinary elastomeric O-ring kind, so as to reduce the complexity of the construction. Also, where the devices are intended as mentioned above for use in a digital system, they will normally be arranged in series mechanically. It is therefore important not only that their adjustment should be capable of being set to very fine limits but that the adjusting means should not obtrude into the area at the end of the cylinder.

According to the invention a pressure-fluid operated positioning device comprises a cylinder and a piston movable therein between stops within the cylinder itself, at least one of the stops being adjustable from outside the cylinder, preferably through the cylinder wall. In a particularly advantageous form of the invention, the cylinder contains two pistons operating piston rods that extend through opposite ends of the cylinder, and fine adjustment stops are provided responsive to adjustment means extending through the cylinder wall. Such an arrangement greatly facilitates the construction of an actuator in which two or more cylinders are arranged end to end with a view to obtaining positional control of, for example, a machine element, in several steps.The adjustable stop or stops may each be on a shaft extending radially through the cylinder wall and arranged, on rotation of the shaft, to give a fine adjustment to the piston stroke. In one form the stop is an eccentric on the shaft, and in another form the stop is on a threaded shaft and comprises a cone co-axial with the shaft and cooperating with a corresponding sloping surface of the piston. In cases where the forces involved would impose too great a load on the, in effect, line contact of the above adjusting means the actual stop member may be a member concentric with the cylinder and within it, and so arranged that it is -given a suitable axial movement, such as by cooperation with ramp surfaces within the cylinder or by a screw threaded connection, which may be rotated for adjustment by means extending through the cylinder wall.The adjustment member may be the end wall itself and according to another aspect of the invention the adjustment is achieved by using threaded elements or cam-like adjusters external to the cylinder by which the end wall may be moved and held in position, while it is sealed to the cylinder by means of a flexible seal, preferably an ordinary O-ring seal. The screw-threaded elements may be in the form of threaded rods passing through radially extending portions of the end wall, the rods having locking nuts to position and adjust the end wall. The rods may form tie rods which connect and fasten together opposite end walls.

According to a further aspect of the invention, a pressure-fluid operated control and positioning system comprises at least two pistons operating in one or more cylinders and arranged mechanicallv in series to move an object to be positioned wherein all of the movement derived from said pistons is in the form of increments acting on the object in the same direction. In a particular form intended for decimal increments, four pistons are used and are arranged to produce four valves of movement, namely 1, 2, 3 and 3. It will readily be seen that, with these integers any movement value from 1 to 9 can be obtained by selecting all at once or only some of them. Thus, for example, a value of 7 can be obtained by selecting 3, another 3 and a 1, and if the maximum of 9 is insufficient the system can be extended by adding a further four pistons having values 10, 20, 30 and 30, and so on.

The system may be designed so that a single numbered control can be operated for selecting any one movement of the object, but the choice of integers 1, 2, 3 and 3 combined with the fact that no subtraction is involved makes it especially easy for an operator to choose the right combination of controls to produce a desired movement of the object. The invention also embraces a floating piston arrangement for reducing the number of cylinders required for a given number of values. In this arrangement, a floating piston is arranged in the same cylinder as a setting piston, the floating piston being movable between stops so as to select one of the required values, and the setting piston being movable between a fixed stop and a movable stop attached to or constituted by the floating piston.By suitable selection of pressures the floating piston may be caused to take up one or other of its two terminal positions so as to impart this alternative to the setting piston. The total length of a multiple series piston and cylinder assembly may thus be reduced.

Where the adjusting device is not a stop with a continuous surface around the inside of the cylinder, it is preferred that the stops are arranged in sets equidistantly disposed around the piston so as to avoid rocking it when it comes up against the stops.

The invention finds especially useful application in applying a setting movement to a fence in a sawmill. For this purpose the use of bistable control valves is preferred with hydraulic or pneumatic operation. The invention is also suitable for numerical control of machine tools under computer input. The valves used may be individually and directly operated, however, as by a hand lever associated with each valve, but preferably each valve is a two-position bi-stable spool valve which conveniently may be provided with a solenoid actuator for moving it in each of the two directions. The solenoids may be controlled by a pushbutton circuit in which each integer or in which each combination of integers has its own push-button switch.

Examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross section through an actuator according to the invention, Figure 2 is a cross section through a solenoid operated spool valve, Figure 3 is diagram of a control circuit for a simplified actuator giving a range of movement between 1 and 9, and Figure 4 is a half section through a set of four pistons and cylinders embodying a further form of construction and adjustment.

Referring first to Figure 1, a positioning actuator comprises a set of four serially arranged cylinders 1, 2, 3 and 4. These contain appropriate pistons mounted on piston rods that are common to pistons in adjacent cylinders, the piston rods at the outer ends of the structure (that is to say, those at the top and bottom in the drawing) being connected respectively to a fixed point and to the object to be moved. The four cylinders thus form a unitary structure which can be extended in length by the actuation of selected pistons.

The pistons are movable within the cylinders by applying pressure-fluid to one side or the other of the pistons, and move between extreme positions, one of which is determined by a fixed stop adjacent to or constituted by the closed end of the cylinder, and the other of which is determined by an adjustable stop (that is to say a stop selectively movable to one or other of two positions) intermediate of the length of the cylinder. In the case of two of the cylinders, additional intermediate floating pistons are provided which can move between predetermined positions so as to provide an adjustable inner end stop for and end piston, or a floating piston may be provided on the rod of one of the two end pistons so as to provide, in effect a movable outer end stop for the piston.The latter form is shown in Figure 1, but in either case three movements can be provided in one cylinder instead of two, with a consequent saving of a certain amount of overall length.

In the example shown, the cylinder 1 has a piston 5, secured to a piston rod 6 through an end plate 7 provided with O-ring seals 8 and 9 between it and the cylinder 1 and the rod 6 respectively. Extending through the cylinder wall is a pair of shafts 1 0, one of which is visible in end view in the drawing, having inwardly directed eccentric extensions 11 which provide back stops for the piston 5 and can be accurately adjusted by rotation so as to control the piston movement to a value of precisely 1 mm. Sealing between the piston 5 and the cylinder 1 is achieved by means of an O-ring 12.

A second piston 13 is arranged on a rod 1 3a and has a total maximum movement of 60 mm.

between a position determined by a pair of back stops 1 5 arranged eccentrically on shafts 1 6 through bores in the cylinder wall and sealed therein by O-rings 17, and at the other extreme by an end plate 14 of the cylinder plus the thickness of a floating intermediate piston 1 8 arranged on the piston rod 13a. A pair of back stops 19 is provided, accurately adjustable, as in the case of the stops previously described, in this case however to provide a movement to the piston 18 of precisely 30 mm. It will be seen that the piston 1 3 has a forward extension 20 that is capable of passing between the stops 1 9 so as to contact the rear of the floating piston 18.Adjustment of the stops 1 9 is achieved by rotation of the eccentric shaft 1 9a which is provided outside the cylinder 1 with a pinned collar 19b. A locking screw 1 9c both locks the collar against rotation, and prevents the shaft 1 9a from being forced out of its bore in the cylinder wall. These locking details are the same for all of the adjustable stops shown in this Figure but have been omitted to improve the clarity of the drawing.

The cylinder 2 and its pistons is functionally a mirror image of the cylinder 1 but since its movement values are different its length will be different, and so will the length of the extension that contacts the face of the floating piston. Thus, the rod 1 3a extends from the cylinder 1 through an end plate 14, through an end plate 36 of the cylinder 2, through a floating piston 37 and to a piston 34. The other end of the cylinder 2 is closed by an end plate 33 through which extends a piston rod 31 attached to a piston 30. Stops 32 are provided to give an accurate movement of the piston 30 amounting to 10 mm. The floating piston 37 is given a movement value of 3 mm. by means of the stops 38, and a further movement value of 3 mm. is provided by the positioning of the piston 34 against the stops 35.

The cylinder 3 is a simple two movement cylinder with the piston 40 spaced away 2 mm.

from the endplate 43 when resting as shown against the stops 42. The other end of the cylinder 3 has a piston 45 on a rod 46 and is spaced away from the endplate a distance of 100 mm. when resting against the stops 45.

The cylinder 4 is another two movement cylinder with the pistons 51, which is also on the rod 46, spaced away 20 mm. from the endplate 52 when resting as shown against the stops 52.

The other end of the cylinder 4 has a piston 54 on a rod 55 and is spaced away from the endplate 56 a distance of 100 mm. when resting against the stops 57.

The rod 6 at the top end of the set of four cylinders is secured to a fixed plate 60 which forms part of a framework which includes a pair of side members 61 having inwardly facing grooves in which a pair of bars 62 can slide. The bars 62 are engaged by notches in the flanges of the endplates 7, 14, 36, 33, 43, 47, 52 and 56 in such a way that the latter are free to slide on the bars 62.

The unit is shown in its fully retracted position from which it is capable of extending, in increments of 1 mm. if required, over a distance equal to the sum of the piston spacings, namely 299 mm. Fluid ports have been shown in Figure 1 indicated by the references 71-84 inclusive, these being schematic only in respect of position and size. In the retracted position shown pressure would be supplied to the ports 71, 73,74,75,76,78,79,81,82 and 84. The ports 72, 77, 80 and 83 are connected to drain. It is believed to be unnecessary to detail every step in the operation of the device. However, pressurisation of the ports 72, 77, 80 and 83 with connection of the remainder to drain will cause the unit to be extended to the maximum in the following manner.It should be understood that the fully extended position corresponds in cases where the device is used to operate a fence in a machine such as a sawmill to the zero position. In this condition the piston 5 will be forced against the endplate 7, so moving the cylinder 1 downwards 1 mm. At the same time the piston 13 and its rod 1 3a will be moved a further 60 mm. downwards, carrying with it the rest of the piston and cylinder structure. Pressure applied to the port 77 will move the cylinder 2 downwards 6 mm. by closing the gaps of the pistons 34 and 37, while the piston 30 and its rod 31 will be moved a further 10 mm. Pressure applied to the port 80 will close the gap of the piston 40 so moving the cylinder 3 down 2 mm. and will move the piston 44 and its rod 46 down a further 100 mm.Finally, pressure applied to the port 83 will close the gap of the piston 51, so moving the cylinder 4 downwards 20 mm., while a further 100 mm. of movement is given by the piston 54 and its rod 55 which is connected to the machine element it is desired to control.

The operation of the unit as a digital positioning mechanism for a machine tool element such as a fence is described below in connection with Figure 3, but in order to understand the principle of operation it should be explained that when selecting a setting from the extended condition described above, it is arranged that any cylinder parts that are connected to drain are so connected through means for maintaining an intermediate pressure, say about half-pressure, between the operating pressure and tank pressure. In this way the unit can be set to any chosen value in the range available by making the appropriate drain and pressure connections.

A suitable valve for use in an electrically operated control circuit is shown in Figure 2. The valve comprises a cylinder body of externally rectangular cross-section and having a port 102 for connection to an appropriate port on the unit described above for supplying or exhausting pressure fluid. The body 101 has a through bore in which is located a sleeve 103 which is ported to circumferential channels 104, 105 and 106, the first of which, 104, communicates with a pair of pressure ports aligned on either side of the body 101 and the second, 105, communicates with a similar pair of drain ports, while the third, 106, communicates with the port 102. Since the pairs of pressure and drain ports are aligned it is possible to multiple the valves by a sandwich construction using sealing rings in the usual way.

The sleeve 103 is sealed to the body 101 by the usual O-rings which are shown but not referenced. A further sleeve 107 is located in the bore and has a pair of internal grooves spaced apart the distance between the ports 104 and 105. A thimble 108 of non-magnetic material such as brass is arranged at each end of the body 101 and supports a solenoid winding 109. Each thimble 108 is provided with a cover 110 and an adjustable end-stop 111. A spool valve element 112 is a sliding fit in the sleeve 013 and serves to connect the port 108 to either the port 105 or the port 104. The spool 112 which is of magnetic material has extended ends which enter the thimbles 108 so as to come under the influence of the field due to the solenoid windings 109 when energised.That part of the spool 112 which lies within the sleeve 107 has a transverse bore containing a pair of spring-loaded balls 11 3 for engagement of the internal grooves of the sleeve 107 so as to ensure that the spool remains in one or other of its terminal positions against the appropriate end-stop 111, according to which of the two solenoid windings 109 has been energised.

Control of a unit as described in connection with Figure 1 may be effected either by valves that are manually operated to supply pressure fluid and to connect to drain appropriate ports of the unit, the valves being suitably coupled so that a unique position is selected by each valve, or such valves may be controlled by an electrical push-button assembly. An example of the latter is shown in Figure 3. In this Figure it will be seen that ten push-button switches are provided, numbered 0 to 9. Each switch has five NO contacts which, when the switch is operated, are bridged by a common moving contact. The contacts of the switches are connected to two sets of busbars, the first of which is indicated by the reference BB1, BB2, BB3 and BB4, which are used to supply current to the setting solenoids a, b, c and d of valves Al, 82, C3 and D3, each of the kind shown in Figure 2. These valves are connected to supply pressure fluid to and exhaust it from a pair of hydraulic cylinders of the kind shown at 3 and 4 in Figure 1. However, the value of the piston movements is in this case 1, 2, 3 and 3, and the suffixes of the references of the setting busbars and of the control valves are indicative of these values. These individual values are set by operation of the solenoids OS 1, OS2, OS3 and OS3', the suffix again indicating the dimension or value chosen.

The values have each on one side a hydraulic pressure connection marked P and a drain connection marked D. On the other side of each valve is an operating connection OP leading to the appropriate port on a cylinder and connectable by the valve to one or other of the connections P and D. Each cylinder has two pistons and the common median part of the cylinder is maintained at half the operating pressure.

The push buttons 0--9 are equipped with latches and with one of the well known interlock mechanisms (not shown) for ensuring that any push button pressed and held by its latch is released by pressing a further button. If necessary, a time lag or a further, hydraulic interlock can be incorporated to ensure that a button subsequently pressed cannot become effective until the command which should follow the pressing of the first button has been carried out.

The two cylinders chosen to illustrate the operation are indicated at 201 and 202. The cylinder 201 contains a piston 203 whose rod 204 is connected to a fixed part 205 of a machine. The piston 206 has a rod 207 which is common to a piston 208. in the other cylinder 209.

A further piston 210 in the cylinder rod 209 has a rod 211 connected to a machine element 212 which it is desired to move. The piston 203 can move between the end of the cylinder and a stop 213 which is adjusted to limit the movement to 1 mm. Likewise a stop 214 limits the movement of the piston 206 to 2 mm., while the stops 215 and 216 limit the movement of the pistons 208 and 210 to 3 mm. each.

In operation, when it is required to set a value on the machine element 212, which may be a fence in a sawmill, the button corresponding to that value is pressed. In the present example the zero position of the element 212 corresponds to the fully extended condition of the actuator constituted by the assembly of pistons and cylinders. Let us assume that the button 5 has been pressed. The effect of this is to apply a voltage from the positive busbar to the busbars BBa and BBd. The busbar BBa is connected to the cancel solenoid a of the valve Al, so that if this valve has been set in the previous operation to supply fluid to the piston 203 it would now be returned to the position where this piston is connected to drain and is returned by the halfpressure in the median common part of the cylinder to a position against the end wall.

The busbar BBd is connected to the cancel solenoid of the valve D3, thus ensuring that the piston 210 is similarly against the end wall of the cylinder 209. At the same time other contacts of the switch apply power to the setting busbars BB2 and BB3. These are connected respectively to the operating solenoids OS2 and OS3 of the valves 82 and C3. The effect of this is to apply full hydraulic pressure to the rod sides of the pistons 206 and 208,moving them 2 mm. and 3 mm.

respectively against the half-pressure in the median part of the respective cylinders. Thus a total movement of 5 mm. from the fully extended position will be applied to the rod 211 and the machine element 212.

In the event that a larger range of movement is required, the system can be extended by using a more complex cylinder arrangement of the kind shown in Figure 3 with suitable changes in the control system.

A simpler system is, of course, possible, by arranging for a single push button to be provided for each of the setting values represented by the valves Al, B2, C3 and D3, so that the operator has to make a mental calculation totalling the setting values to add up to the setting that is required. In this case it will be convenient to incorporate a switch in either the positive or negative electrical feed controlled by a "Set" push button, so that a dimension can be set up on the other push buttons, and when the total has been checked as indicated by the buttons that are down or pilot lights illuminated, then the "Set" button can be pushed to cause the setting movements to be applied.Such a system can be purely hydraulic, if desired, by arranging that the spools of the valves themselves be manuaily operated by push buttons or otherwise, and similarly provided with interlocks during a machining operation.

Although the systems and components have been described herein as being applied to a hydraulic system, it will be appreciated that pneumatic operation is equally possible.

It will be appreciated that with the devices described above, and especially in the case of pneumatic operation, any reaction on the element that is being positioned will be resisted, at least in one direction, only by the applied fluid pressure. It is therefore envisaged that, after a setting movement has taken place, a locking operation can be automatically instituted. By way of example, a fluid-pressure operated collet which locks the final piston rod can be put into effect immediately after the element arrives at its set position.

It will also be appreciated that, although the adjustable stops to limit the travel of the pistons are described above as back stops, if the system were reversed they would become forward stops to arrest the forward movement of the piston.

In Figure 4 the cylinders are arranged in pairs with the two pistons of each pair having piston rods extending through oppositely facing end walls and, since the principle of construction and of operation of both pairs is the same, only the upper pair shown in the drawing will be described in detail.

The upper pair of cylinders is constituted by rings or barrels 310 and 31 A piston 312 fabricated from a plain disc 313 and a disc 314 is slidable within the ring 310 and is sealed thereto by means of an O-ring 315, the two discs being held together on the shoulder of a piston rod 316 by a screw 317 in the end thereof.

The cylinder formed by the ring 310 is completed by end caps 318 and 319 which are sealed against the cyiindrical surface of the ring 310 by O-ring seals 320 and 321. In this example the external surface of the ring 310 is used since it is desired to make the unit as compact as possible; it will usually be necessary, however, to machine both the inner and outer surfaces of the ring 310 in order to ensure adequate concentricity of the two surfaces. If, however, added length can be tolerated, it would be possible to effect the seal on the inside surface of the ring.

The end cap 318 is completed by a blanking plate 323 to which it is sealed by a further O-ring 324, and constitutes one of the end stops for the piston 31 4. The other end stop is constituted by an inward projection 325 of the end cap 319, which may be integral or separate and is sealed to the piston rod 31 6 by a further O-ring 326.

The assembly is held together by a number of tie rods 327 equidistantly arranged around the cylinder and extending through holes in the respective end caps. Only one of these rods is illustrated, so as to simplify the drawing. It will be appreciated that the extent of the movement of the piston is primarily determined by the length of the ring 310 and the manufacturing tolerances experienced in producing the end caps 31 8 and 31 9. However it is not commercially practicable to maintain these tolerances to the accuracy that may be required of the piston movement especially in a setting actuator for a machine tool element. Moreover a degree of wear may take place for which compensation needs to be made.

Thus final adjustment is therefore achieved by adjusting clamp nuts 328, 329 up or down the threaded tie rods 327 which are located with respect to the end cap 31 8 by nuts 330. After final assembly, the movement of the piston is adjusted by moving the nuts 328, 329 up or down the threaded tie rods 327 which for this purpose may be provided with a fine thread. By way of example, it can be seen that with a pitch of twenty five threads per inch a rotational movement of 1 on the adjusting nuts will given an adjustment of 1/9000th of an inch.

The other cylinder of the pair is constructed in an exactly similar manner with end caps 331 and 332 sealed by O-rings 333,334 to the outside of the ring 311, and the blanking plate 323 being common to both cylinders. A further seal is provided on the blanking plate for the lower cylinder as shown.

The length of the rings 310, 311 is chosen to give appropriate dimensional movements to the piston rods, and the two further cylinders 333 and 334, the latter of which has a common piston rod with the cylinder 311. As in the case of the construction shown in Figure 1, it is preferable for applications such as machine tools that settings from a zero position should be achieved without subtractive movements, so a combination such as 1, 2, 3, 3 will cover digital settings from zero to nine. However, other combinations are possible.

The four cylinders forming a complete actuator have a piston rod at one end secured to a fixed point as shown at 335 and a piston rod 316 at the other end secured to the machine or other element it is desired to move. The cylinders may, if desired, be supported in a slide to minimise deflection.

In the drawing the parts have been shown with the adjustments secured by the nuts 328, 329 in the minimum position, so that the respective rings are in contact with the end caps. Adjustment away from this position will result in a slight gap at the ends of the ends of the rings and the rings will be free to float endwise by this amount.

Claims (15)

Claims

1. A pressure-fluid operated positioning device comprising a cylinder and a piston movable therein between stops within the cylinder itself, wherein at least one of the stops has adjusting means which includes an operable part external to the cylinder and not extending along its axis.

2. A device according to claim 1 wherein the cylinder comprises a tubular wall member terminated by end caps sealed to the wall member by compression type seals.

3. A device according to claim 1 or claim 2 wherein the adjusting means for the stop comprises a number of shafts extending through the cylinder wall and each having a cam surface acting as a stop for a piston sliding within the cylinder.

4. A device according to claim 3 wherein each shaft is journalied in a bore extending transversely through the cylinder wall and has an eccentric cam surface within the cylinder and forming a stop for the piston.

5. A device according to claim 1 or claim 2 wherein adjustment of the length of stroke is effected by moving an end wall of the cylinder, which wall constitutes or carries a stop for the piston.

6. A device according to claim 5 wherein the end wall is positioned by locking nuts on threaded shafts passing through radially extending portions of said end wall.

7. A device according to claim 6 wherein the threaded shafts form tie rods which connect together opposite end walls.

8. A device according to claim 7 wherein a pair of cylinders is arranged back to back on the same set of tie rods.

9. A device according to claim 8 wherein the cylinders have a common end wall.

10. A device according to any one of the preceding claims wherein a cylinder is additionally provided with a floating piston which carries or constitutes a stop for the other piston so as to provide it with an intermediate stop position.

11. A pressure-fluid operated control and positioning system comprising at least two pistons operating in one or more cylinders and arranged mechanically in series to move an object to be positioned, wherein all of the movement derived from said pistons is in the form of increments acting on the object in the same direction.

1 2. A pressure-fluid operated control and positioning system according to claim 11 wherein a base zero position of an object to be positioned corresponds to a fully extended or fully retracted condition of a number of serially arranged piston and cylinder combinations, the operation of each piston stroke being selected by pressing the appropriate button in a panel of buttons each marked with the dimension of the appropriate stroke.

1 3. A system according to claim 12 wherein valves for operating selected pistons or electrical circuits controlling said valves are preselected in accordance with the dimensional movement to be imparted to a member to be controlled and are subsequently rendered operative by a setting valve or control.

14. A system according to claim 13, the arrangement being such that the pistons must all be returned to a zero position before the setting control can be operated again.

15. A system according to claim 13 or claim 14 wherein the initial preselection is displayed for checking prior to operation of the setting valve or control.

1 6. A system according to any one of claims 11 to 1 5 wherein supply of pressure-fluid to the pistons is controlled by bi-stable devices so that pressure on selected pistons is maintained until a resetting operation is concluded.