Linear Actuator

Abstract

A linear actuator (10) for use in a modular assembly of such actuators comprises an actuator body (11), a shaft (12) guided by the body to be displaceable relative thereto in the sense of tlte longitudinal axis (13) of the shaft and a drive motor enclosed in the body and operable to axially displace the shaft relative to the body in two mutually opposite directions. The body has two mutually opposite sides (15a, 15b) respectively lying in two substantial parallel spaced-apart planes, which each represent a reference plane for positioning the body side-by-side with the body of another such actuator, and a further side (17b) connecting the two mutually opposite sides and stepped to form a projection (18) receiving the shaft (12) with the axis (13) parallel to the two planes and a rebate (19) beside the projection to permit the body to interlock with the body of another such actuator at that further side. The projection (18) and rebate (19) are of substantially the same width in the sense of the spacing of the two planes and the shaft (12) is disposed substantially centrally of the projection (18) so that when the body (11) is interlocked with that of another such actuator the pitch of the shaft axes (13) is equal to that width.

Claims

1. A linear actuator for use in a modular assembly of such actuators, the actuator comprising: a actuator body; a shaft having a longitudinal axis and guided by the body to be displaceable relative thereto in the direction of the longitudinal axis of the shaft; and a drive motor supported by the body and operable to axially displace the shaft relative to the body in two mutually opposite directions, the actuator body having two mutually opposite sides respectively extending in two parallel spaced-apart planes which each represent a reference plane for positioning the actuator body and a further side connecting the two mutually opposite sides and stepped to form a projection receiving the shaft with the longitudinal axis thereof parallel to the two parallel spaced-apart planes and the rebate beside the projection, the projection having a projection width that is the same as the rebate width with respect to the spacing of the two parallel spaced-apart planes and the shaft being disposed centrally of the projection in.

2. The linear actuator according to claim 1, wherein the body comprises a casing supporting and enclosing the motor.

3. The linear actuator according to claim 1, wherein the actuator body comprises a frame and the motor is supported by structural elements of the frame.

4. The linear actuator according to claim 1, wherein at least one of the two opposite sides is formed by a continuous surface area extending in one of the two parallel spaced-apart planes.

5. The linear actuator according to claim 1, wherein at least one of the two opposite sides is formed by a plurality of discrete surface areas lying in the respective one of the two parallel spaced-apart planes.

6. The linear actuator according to claim 1, comprising a mechanically positive drive transmission arranged to transmit drive from the motor to the shaft.

7. The linear actuator according to claim 6, wherein the mechanically positive drive transmission comprises a rack extending along the shaft and a pinion meshing with the rack and rotatable by the motor.

8. The linear actuator according to claim 1, comprising a mechanically non-positive drive transmission arranged to transmit drive from the motor to the shaft.

9. The linear actuator according to claim 8, wherein the mechanically non-positive drive transmission comprises a friction surface extending along the shaft and a friction wheel frictionally engaging the friction surface and rotatable by the motor.

10. The linear actuator according to claim 6, comprising a worm wheel and worm interposed between the motor and the transmission, the worm wheel being coupled to the transmission at a drive input thereof and the worm being drivingly engaged with the worm wheel and coupled to the motor at a drive output thereof.

11. The linear actuator according to claim 10, wherein the worm wheel is rotatable in opposite directions of rotation by the motor and non-rotatable in either of those directions by the worm wheel.

12. The linear actuator according to claim 1, wherein the shaft is a solid rod.

13. The linear actuator according to claim 1, wherein the shaft is a tube.

14. The linear actuator according to claim 13, wherein the tube is connectible with fluid conveying means and defines a conduit for a fluid medium from the fluid conveying means.

15. The linear actuator according to claim 13, wherein the tube is connectible with a device and defines a conduit for at least one conductor to or from the device.

16. The linear actuator according to claim 1, comprising optical sensing means for sensing two spaced-apart end positions of the shaft relative to the actuator body.

17. The linear actuator according to claim 16, the optical sensing means being operable to emit light for incidence on the shaft and to respond to reflection of light from the shaft at each of the two end positions.

18. The linear actuator according to claim 1, wherein the actuator body is usable in either one of two mutually inverted orientations with the shaft extending vertically and comprises means for determining in which of the two orientations the actuator is disposed.

19. The linear actuator according to claim 1, comprising electrical connection means provided at each of an intended top and at an intended bottom of the actuator body to in use allow electrical connection to the actuator selectably from either or each of above and below the actuator.

20. The linear actuator according to claim 1, wherein the actuator body has at least one passage for reception of guide means to guide displacement of the actuator perpendicularly to the two parallel spaced-apart planes.

21. The linear actuator according to claim 1, the actuator and a second actuator being connected together to form an assembly in which the longitudinal axes of the shafts of the actuators of the assembly are disposed in a line.

22. The linear actuator according to claim 21, wherein the assembly is composed of a number of the actuators with the bodies thereof positioned in the interlocking relationship and a number of the actuators with the bodies thereof positioned in the side-by-side relationship.

23. A machine comprising an assembly according to claim 21, and control means for controlling the motors of the actuators of the assembly to displace the shafts of the actuators.

24. The machine according to claim 23, the control means being operable to cause the motors to displace the shafts of the actuators individually in a predetermined sequence.

25. The machine according to claim 23, the control means being operable to cause the motors to displace the shafts of the actuators in groups, wherein the shafts in each group are displaced simultaneously.

26. The machine according to any one of claims 23, the control means being operable to cause the motors to displace all the shafts of the actuators simultaneously.

27. The machine according to claim 23, comprising displacing means for displacing the assembly perpendicularly to the two parallel spaced-apart planes of each actuator.

28. The machine according to claim 23, the machine being a pipetting machine in which the pitch of the longitudinal axes of the shafts of the actuators of the assembly corresponds with a given pitch of a plurality of receptacles for liquid samples.

29. The machine according to claim 28, wherein the given pitch is the pitch of the wells of a well plate of a standard format.

30. The machine according to claim 28, wherein the assembly is oriented so that each of the shafts of the actuators thereof is raisable and lowerable by the axial displacement of the shaft by the drive motor of the actuator and is equipped for co-operation in a lowered position with a respective receptacle for a liquid sample.

31. The machine according to claim 30, wherein each of the shafts is equipped with means for at least one of discharging liquid into and inducting liquid from the respective receptacle.

Description

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0025] A preferred embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

[0026] FIG. 1 is a schematic perspective view of a linear actuator embodying the invention, from one side, the top and the front;

[0027] FIG. 2 is a schematic perspective view of the actuator of FIG. 1 from the same side, the top and the back;

[0028] FIG. 3 is a schematic plan view, to enlarged scale, of the actuator of FIGS. 1 and 2;

[0029] FIG. 4 is a schematic sectional view, to reduced scale, on the line IV-IV of FIG. 3;

[0030] FIG. 5 is a schematic perspective view of an assembly of linear actuators each corresponding with that of FIGS. 1 to 4;

[0031] FIG. 6 is a diagram showing a first configuration of four actuators in an assembly such as that of FIG. 5; and

[0032] FIG. 7 is a diagram similar to FIG. 6, but showing a second configuration of the actuators.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0033] Referring now to the drawings there is shown a linear actuator 10 for use in forming a modular assembly 40 (FIGS. 5 to 7) of such actuators, the actuator comprising an actuator body 11, a shaft 12 guided by the body to be displaceable relative thereto in the sense of the longitudinal axis 13 of the shaft, and a speed-controllable, reversible-drive electric motor 14 (FIG. 4) enclosed in and supported by the body and operable to axially displace the shaft in two mutually opposite directions. In the actuator orientation shown in the drawings, those directions are vertically up and down, thus along a Z-axis, but the directions can be in any sense depending on the selected actuator orientation.

[0034] The body 11 is of substantially parallelopipedonal form with, in particular, two mutually opposite planar sides 15a and 15b which form major faces of the body and respectively lie in two substantially parallel spaced-apart planes 16, each plane representing a reference or contact plane for side-by-side positioning of the body 11 against that of another such actuator. The spacing of the two planes 16 determines the width w of the body 11. By way of example, the width can be 18 millimetres, which is a dimension characterising twice the spacing of adjacent wells in a well plate (see further below). The two sides 15a and 15b are connected by two further sides 17a and 17b, which again are mutually opposite and which constitute minor sides of the body. One of the further sides 17a is planar, but the other 17b is stepped to form a projection 18 and a rebate 19 beside the projection, each of the projection 18 and rebate 19 being of substantially the same width in the sense of the spacing of the two planes 16. Hence each of the projection 18 and the rebate 19 has a width w/2 equal to half the width w of the body 11. The body is completed by two further sides 20a and 20b, which in the illustrated orientation of the actuator respectively form a substantially planar upper face and a substantially planar lower face.

[0035] The body 11 has the form of a hollow casing, preferably formed for the major part (excepting the projection 18) by a box-like shell which has a cavity and which is a casting, a CNC-machined metal component, a three-dimensional printed article, a moulding of high-density plastics material, a layered composite of carbon-fibre or other high-strength synthetic or a body produced by any other suitable material and/or by any other suitable method. The cavity is open at one of the sides 15a and 15b, here the side 15a, of the body and is closed by a plastics material cover removable to provide access to the cavity.

[0036] Although the body 11 of the actuator 10 would normally have the form of an entity, it is possible for the body to be a component with one or more separate outlying elements or spacers co-operating with the component to form the body. The term “body” is thus to be regarded as also embracing separately constructed parts disposed in association with one another to provide a unit.

[0037] The shaft 12 guided by the body 11 is disposed centrally in the projection 18, specifically slidably received in a bore passing through the projection such that the axis 13 of the shaft is substantially parallel to the planes 16 and also substantially perpendicular to the two sides 20a and 20b of the body 11. Sliding guidance of the shaft 12 in the bore of the projection 18 is provided by two bearing bushes 21 of slide-bearing material, such as bronze or a hard thermoplastics material, fitted in the bore at its opposite ends. The shaft 12 itself can be a solid rod or a tube, here a tube with a through bore intended as a conduit for a fluid or for a filament or filaments, such as electrical or optical conductors. Depending on the use of the actuator 10 the shaft 12 can be provided at either or each end with attachment means, for example a screw thread, for detachably securing a fitting of any desired kind or directly with the fitting itself.

[0038] Apart from positioning of the body 11 of the actuator 10 in side-by-side relationship with the body of at least one other such actuator as mentioned above, thus areal contact of two such bodies at their reference planes, a particular feature of the configuration of the body with the projection 18 and rebate 19 of corresponding width and the arrangement of the shaft 12 to extend centrally through the projection 19 is a capability of the body 11 of the actuator to interlock at the side 17b with the body of another such actuator, specifically an interlock produced by the engagement of the projection 18 of each actuator in the rebate 19 of the respective other actuator. For that purpose, the two actuators participating in the interlock are turned through 180 degrees so as to be juxtaposed as shown in FIGS. 5 to 7. In that case, the longitudinal axes 13 of the shafts 12 of the two interlocked actuator bodies will necessarily have a pitch, thus a shaft axial spacing, equal to the width of each projection 18 or rebate 19, i.e. w/2. The pitch is accordingly equal to half the width of the spacing w of the two spaced-apart planes 16 in which the sides 15a, 15b or major faces of the body 11 lie.

[0039] With respect to the side-by-side relationship it is possible for one pair of interlocked actuators 10 to be inverted relative to an adjoining pair of interlocked actuators 10, which is facilitated by construction of the body 11 of the individual actuator to be of substantially symmetrical external form with respect to a bisecting horizontal plane.

[0040] In order to enable interconnection of assembled actuators to form a rigid assembly 40 the body 11 of the actuator 10 is formed at each of the sides 20a and 20b with a recess 22 adjacent to and also extending over the projection 18. Each recess 22 serves to receive a connecting bracket (not shown), which is fixed to the body 11 by way of a set screw (not shown) engaged in a threaded bore 23 of the body 11 and which is similarly fixed to the bodies of the other actuators making up the respective assembly. Interconnection of the actuators by other methods is, of course, also possible.

[0041] In addition to the recesses 22, the body 11 is formed adjacent to the side 17a and therefore remote from the projection 18 and rebate 19 with two through bores 24 which are in addition respectively adjacent to the two sides 20a and 20b, the bores 24 thus opening at the two major sides 15a and 15b. The two bores 24 serve to receive guides (not shown) along which the actuator 10 or an assembly of such actuators can be displaced perpendicularly to the planes 16. The sense of this displacement depends on the respective orientation of the actuator or actuators, but is an X or a Y axial direction in the case of Z-axis shaft displacement

[0042] The electric motor 14 provided for displacement of the shaft 12 relative to the body 11 is mounted in the cavity of the casing, which is defined by the body 11, by way of a chassis 25 and transmits drive to the shaft 12 by way of a rack and pinion transmission. The transmission consists of a rack 26 which extends along the shaft 12, in particular is formed integrally therewith by machining, at a side of the shaft facing towards the motor and of a pinion 27 which meshes with the rack and is rotatably mounted on the chassis 25 by way of an axle (schematically indicated by its axis). Interposed between the motor 14 and pinion 27 of the rack and pinion transmission is a worm 28 and worm wheel 29, the worm wheel being mounted on the same axle as the pinion 27 and optionally connected to or formed integrally with the pinion and the worm being disposed in driving engagement with the worm wheel and rotatably mounted in the chassis 25 by way of an axle. The worm 28 is in turn drivably coupled to the output of the motor 14 by way of a gearwheel or pinion train 30.

[0043] The transfer of drive via the intermediate worm 28 and worm wheel 29 precludes reverse driving by the shaft and thus undesired gravitationally-induced displacement of the shaft. The motor 14 can transmit drive to the shaft 12 via the gearwheel train 30, worm 28, worm wheel 29, pinion 27 and rack 26, but reverse transmission of drive by the shaft 12 via the rack 25, pinion 26 and worm wheel 28 is blocked at the point of interengagement of the worm wheel 29 and worm 28.

[0044] Detection of shaft position for the purpose of control of displacement by way of the motor drive is achieved through two optical sensors 31 serving to detect predetermined end positions of the shaft. Each sensor 31 comprises a light emitter located in the cavity of the body 11 in the vicinity of a respective end of the bore through the projection 18 and arranged to emit light in the direction of the shaft 12, the light being conducted through a respective passage which opens into the bore at the side of the shaft 12 provided with the rack 26. The rack is interrupted at a predetermined location by a flat 26a which, when aligned with each passage, reflects the emitted light to significantly greater extent than when any part of the rack is aligned with the passage, the light reflection by the rack being diffuse. The sensors 31 each respond to the increased level of reflected light to report attainment of an associated shaft end position and thereby trigger, for example, stopping or reversal of the motor operation. By this simple means the shaft 12 can be displaced in either direction and arrested when it has reached an intended end position.

[0045] Also mounted in the cavity is a printed circuitboard 32 carrying electronic control components providing operation and control of, inter alia, the motor 14 and optical sensors 31. Power supply and signal transmission are carried out via duplicate electrical connectors 33 provided at each of the sides 20a and 20b, use being made of either or both connectors as required. Provision of duplicate connectors allows, in the case of inversion of actuators within an assembly 40, input and output at a single side of the assembly. Motor control is also influenced by signals from a magnetic encoder (not shown) provided at the axle carrying the pinion 27 and worm wheel 29. Further, an accelerometer can be included to determine orientation of the actuator 10 in an assembly, since in the case of an inverted actuator the motor drive direction will be the reverse of that of a non-inverted actuator and the motor control adapted accordingly. Finally, the body 11 can be provided at the side 17a with cooling openings 35 to exhaust motor operating heat.

[0046] Use of the actuator 10 in creation of the modular assembly 40 is evident from the foregoing description. As can be seen in FIG. 5, which shows the assembly to be composed of four side-by-side pairs of interlocked actuators 10, optimum compactness is achieved in X and Y directions. The bodies 11 of the eight actuators 10 making up the assembly are interconnected by the afore-mentioned brackets (not shown), which are secured by set screws screwed into the threaded bores 23, to form a rigid unit in which the eight shafts 12 of the actuators are arranged with their longitudinal axes 13 disposed in a line at a substantially constant pitch. In the case of design of the actuator for use in creating an assembly intended for, for example, a pipetting machine the pitch of the shaft axes 13 is preferably 9 millimetres to correspond with the well spacing in a well plate of standard format. In operation of such a machine, the motors 14 of the actuators 10 making up the assembly 40 are operated and controlled by way of supply of current to provide reciprocating displacement of the shafts 12 between their predetermined—here upper and lower—end positions. In their lowered end positions, the shafts can co-operate in appropriate manner with appropriate individual targets, here the wells of a well plate, to or from which measured volumes of sample liquid can be transferred. In the raised end positions of the shafts the assembly as a whole can be displaced in X and/or Y direction to, for example, step the line of shafts between successive rows of wells or to displace the line of shafts along an individual row when the number of wells in a row is greater than the number of shafts in the respective assembly.

[0047] In such a machine, the motors 14 of the actuators 10 can be controlled to axially displace the shafts, for example, simultaneously as a whole, in groups or one at a time, perhaps sequentially, depending on requirements. However, the shafts are axially displaced individually in the sense that each is driven by an individual motor and Z axis shaft motion does not require movement of the assembly itself for that purpose. A considerable degree of freedom in selection of the pattern of displacement of the shafts 12 is therefore possible, for which purpose a pipetting machine incorporating such an assembly 40 can include a superordinate control influencing the control exercised by the individual control means of the actuators 10, particularly the timing of the operation of the motors 14.

[0048] The tubular shafts 12 in the machine can be employed directly as fluid conduits, such as for conveying liquid by a conveying device or merely by gravity, or inducting liquid by suction. Depending on use of the assembly, the fluid can be not only a liquid, but also a gas, such as compressed air or air at sub-atmospheric pressure. The tubular shafts can also be used, for example, as feeds for conductors to devices provided at the lower ends of the shafts.

[0049] FIGS. 6 and 7 show, in self-explanatory manner, two different possibilities of arrangement of, by way of example, four actuators. In FIG. 6, two pairs of interlocked actuators are arranged in side-by-side relationship without inversion, whereas in FIG. 7 one pair of interlocked actuators is inverted relative to the other, as indicated by the transposition of the references 20a and 20b denoting the actuator sides nominally upper and lower in an orientation of the actuator for vertical axial displacement of its shaft.

[0050] The actuator 10 hereinbefore described thus makes it possible, by virtue of the configuration of the body 11 and disposition of the shaft 12, to construct a modular assembly of actuators which is of particular compact form and which has the individually driven shafts disposed at a predetermined pitch spacing in which, in effect, two shafts are accommodated in the width of a single actuator.