GB2097197A - Combined motion drive unit - Google Patents

Abstract

A combined motion drive unit (10) comprises two rotary electric stepping motors (28, 30) arranged in a common casing. The motor (28) includes a rotor (36) fixed to a shaft (18) of the unit whereby the shaft (18) can be rotated to any one of a desired plurality of angular positions by energising the motor (28). Fixed to a rotor (42) of the second motor (38) is an externally threaded sleeve or lead screw (44) received in a nut (46) fixed to the casing. When the motor (30) is energised, the rotor (42) thereof and the lead screw (44) rotate, whereby the lead screw (44) is screwed into or out of the nut (46) with the result that circlips (52, 54) cause corresponding axial movement of the shaft (18) without subjecting the shaft (18) to rotary movement. The shaft (18) can thus be moved axially in predetermined steps corresponding to the step positions of the motor (38). The above-described rotational and axial movements of the shaft (18) are mutually independent. <IMAGE>

Description

SPECIFICATION Combined motion drive unit This invention relates to combined motion drive units.

According to the invention there is provided a combined motion drive unit comprising: a casing, a shaft housed in the casing, first drive means incorporated in the casing and operative to rotate the shaft, and second drive means incorporated in the casing and operative to translate the shaft along its axis, the first and second drive means being such that they can be selectively energised to provide mutually independently controllable axial and rotational motion of the shaft.

The respective drive means may comprise motors. According to preferred embodiments of the invention described hereinbelow, the motors are electric motors. However, for various reasons, for example in an environment where electrical apparatus may be dangerous, other types of motors (e.g. pneumatic motors) can be employed.

Some other form of drive means than a motor (rotary or linear) may be used in some applications. For instance, the second drive means may comprise a solenoid arrangement in some cases.

At least one of the motors, electric or otherwise, may comprise a stepping motor,that is to say a motor which moves between a variety of predetermined positions rather than a motor which is continously variably movable between undefined positions. When both motors are stepping motors, the unit may be provided with energisation means operative to energise the motors in such a manner as to cause the shaft to move axially and/or rotationally to any one of a plurality of desired positions.

Such an arrangement has the advantage that the shaft can be positioned exactly where desired, both rotationally and axially, simply by appropriately energising the stepping motors. Such an arrangement is of particular advantage when precise positioning in both series is required, as for example in a preferred application of the invention described hereinbelow in which the unit is used to drive a print head. However, if driving in this manner is not appropriate for one reason or another, or if accurate positioning is not a crucial requirement, means can be provided to terminate movement of the shaft when it has detected that the shaft is in a desired position.

One preferred application of a drive unit in accordance with the invention, mentioned briefly above and described in more detail below, is to driving a print head in a printing device. The invention is, however, useful in various other applications, some of which are described hereinbelow.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 is an axial section through a first combined motion drive unit embodying the invention; Figure 2 is an axial section through a second combined motion drive unit embodying the invention; Figure 3 is a section of the unit of Fig. 2 taken along the line Ill-Ill in Fig.2; Figure 4 is a schematic view of a printing device incorporating a combined motion drive unit embodying the invention; Figure 5 is a largely sectional view of a robot gripper or manipulator mechanism incorporating a combined motion drive unit embodying the invention;; Figure 6 is a partial sectional view through part of a scanning or tracking mechanism incorporating a combined motion drive unit embodying the invention, the view being taken along the line VI-VI in Fig. 7; Figure 7 is a top plan view of the structure shown in Fig.6; Figure 8 is a schematic view of a clutch and/or brake mechanism incorporating a combined motion drive unit embodying the invention; and Figure 9 is a schematic view of a variable speed drive/gear change mechanism incorporating a combined motion drive unit embodying the invention.

Fig. 1 of the drawings shows a combined motion drive unit 10 having a casing constituted by a tubular main part 12, a front end frame 1 4 and a rear end frame 1 6. A shaft 1 8 is held in and extends axially of the casing, the shaft being received in bearings 20 and 22 so as to be capable of both rotation about and translation along its longitudinal axis. The bearings 20 and 22 are held in the front frame 1 4 and the rear frame 16, respectively, by means of respective circlips 24 and 26.

The casing of the unit 10 incorporates a first rotary electric stepping motor 28 and a second rotary electric stepping motor 30. The first motor 28 comprises a stator formed by a core 32 and windings 34. The first motor 28 further comprises a generally disc-like rotor 36, which is fixed by and anti-backlash coupling (not shown) to the shaft 1 8 for rotation and translation therewith.

The second electric stepping motor 30 comprises, like the first motor 28, a stator formed by a core 38 and windings 40. The second motor 30 further comprises a disc-like rotor 42 generally resembling the rotor 36 of the motor 28. However, the rotor 42 is not fixed to the shaft 18, but is instead fixed to a sleeve 44 which is externally threaded to form a tubular lead screw. The lead screw 44 surrounds the shaft 1 8 but is not fixed to the shaft 1 8. The lead screw 44 is screwed into an anti-backlash nut 46 (the details of the anti-backlash arrangement not being shown) which is fixed in a nut seating ring 48 which is in turn fixed over a boss portion 50 of the rear end frame 1 6 of the casing.A pair of circlips 52,54 arranged at opposite ends of the tubular lead screw 4-4 ensure that while the shaft 1 8 does not rotate upon rotation of the assembly 42 and the lead screw 44 it moves axially in response to axial movement of such assembly.

The manner of operation of the combined motion drive unit 10 of Fig.1 will now be described.

If rotary movement of the shaft 1 8 is required, the first motor 28 is energised appropriately and drives the shaft to rotate. Since the shaft 1 8 and the assembly of the rotor 42 and lead screw 44 are not arranged to rotate together, such rotary motion is not at least in theory transmitted to the rotor 42. In practice, if some such rotary motion is transmitted to the rotor 42, it may be necessary to energise the motor 30 such that the rotor 42 is stationary, i.e. does not rotate.

If translational (axial) movement only of the shaft 1 8 is required, the second motor 30 (but not the first motor 28) is energised to rotate, whereby the rotor 42 and the lead screw 44 rotate. (Again, it might in practice be necessary to energise the motor 28 to remain stationary, i.e. not to rotate.) The lead screw 44 is therefore screwed into or out of the nut 46 depending upon the direction of rotation of the rotor 42. The resultant axial motion of the lead screw 44 and the rotor 42 is transmitted via the circlips 52 and 54 to the shaft 18, whereby the shaft 1 8 moves axially. Not being driven in rotation, the shaft 1 8 simply moves axially and does not rotate.

Thus, as explained above, the shaft 1 8 can be moved both axially and rotationally by selective energisation of the motors 28, 30, such two motions being mutually independently controllable by selective energisation of the two motors.

As will be appreciated by those familiar with stepping motors, with the above arrangement the shaft 1 8 can be rotated to any desired one of a plurality of rotational position steps (corresponding to the step position of the motor 28) by appropriately energising the motor 28 and can be translated to any one of a plurality of desired axial position steps (corresponding to the angular position step of the motor 30 by energising the motor 30.

The extent of permitted axial motion is dictated by the fact that the rotors 36,42 move axially with the shaft 1 8. The maximum amount of axial movement of the shaft 1 8 is over a distance shown in Fig. 1, such movement being in a inward sense from the illustrated position which shows the shaft fully extended.

Figs. 2 and 3 show a combined motion drive unit 10' which is similar in many respects to that shown in Fig.1 and which will therefore be described only in so far as it differs therefrom. Items in Figs. 2 and 3 which are the same as or similar to items described above with reference to Fig. 1 are designated by the same reference numerals with prime superscripts.

An important feature of distinction of the unit 10' of Figs. 2 and 3 over the unit 10' of Fig.1 is that the extent of axial movement of the shaft 18' of the unit 10' is, at least in theory, indefinite. The shaft 18' is formed as a lead screw which is threaded along its whole length or at least along the length which, in use, will be received within the rotors 36',42'. The shaft 18' extends through clearance holes 60,62 in the end frames 14' and 16', respectively. The shaft 18' also extends through clearance bores 64, 66 in the rotors 36' and 42', respectivley, and through a clearance bore of a collar 68 fixed as shown to the rotor 36' of the motor 28'.

The nut 46' is, in the present embodiment, screwed onto the lead screw (shaft) 18' and is fixed to the rotor 42' of the second motor 30' for rotation therewith. The rotor 36', the collar 68, the rotor 42' and the nut 46' are all restrained against axial movement by three sets of ball bearings 70 arranged where shown in Fig. 2.

The rotor 36' of the first motor 28' is connected to the shaft (lead screw) 18' by connection means that will transmit rotary movement of the rotor to the lead screw without preventing axial movement of the lead screw. Such means comprises three rows of ball bearings 72, each row being held partly in axial grooves 74 on the surface of the lead screw and partly in axial grooves 76 in the inner surface of the collar 68.

The unit of Figs. 2 and 3 is operated in the following way. To obtain rotary motion only of the shaft (lead screw) 18', the motors 28',30' are both driven in the same direction and in synchronism. The rotation of the rotor 36' of the first motor 28' is transmitted to the shaft 18' by the connection means 72,74,76 to cause the shaft 18' to rotate. The rotation of the rotor 42' of the second motor 30' causes the nut 46' to rotate at the same speed as and in synchronism with the shaft 18', whereby there is no relative movement of the nut 46' and shaft 18' and the shaft 18' is therefore not subjected to axial (linear) movement.

For linear or axial movement only of the shaft 18' the first motor 28' is energised in a sense to maintain it stationary, and the second rotor 30' is energised to rotate; The fact that the rotor 36' of the first motor 30' is held stationary causes the shaft 18' to be prevented from rotating by the connection means 72,74,76. The rotation of the motor 30' causes rotation of the nut 46' whereby relative screwing motion of that nut and the shaft 18' causes linear motion of the shaft 18'.

Both the unit 1 0 described with reference for Fig. 1 and the unit 10' described with reference to Figs. 2 and 3 can be used in a variety of applications. By way of example only, some of these applications will be described below. For convenience, in the following part of the description, reference is made only to the unit 10 of Fig. 1 and to components thereof. It should be understood, however, that in each of the following cases, the unit 10' of Figs. 2 and 3 could be used instead of the unit 10 of Fig. 1.

One particularly preferred application of the drive unit 10 is to driving a print head of a formed character impact printer of the daisy wheel type. As is generally well known, a daisy wheel print head comprises a plurality of elongate flexible elements or 'petals' extending radially from a hub and bearing print characters at their free ends. Printing of a desired characteris effected by rotationally indexing the daisy wheel until a desired character is in a print position, whereupon it is struck against a platen to effect printing.

Successive characters are indexed in turn to the print position and struck, in the above manner, to continue printing.

A variant of the daisy wheel print head, referred to herein as a 'thimble', essentially comprises a daisy wheel with the petals or elongate resilient elements bent at right angles approximately half way along their lengths so that their outer portions extends axially rather than radially. The result is a device having a smaller diameter and lower inertia than a daisy wheel. Moreover, if the wheel can be moved axially as well as radially, and the print characters are spaced axially, for example arranged in two or more levels or rings spaced axially from one another, more than one row of print can be accommodated.As can be appreciated, the number of rotary indexing positions can be reduced in proportion to the number of such level or rings, or the number of characters that may be printed can be increased in proportion to the number of such levels or rings.

Fig. 4 shows a thimble type of print head 80 mounted on the shaft 1 8 of a combined motion drive unit 1 0. As described above, the thimble 80 comprises a plurality of elongate resilient elements which extend radially away from the hub (not shown) fixed on the shaft 1 8 and are then bent to extend generally axially of the shaft 1 8. Such an arrangement is, as will be appreciated, extremely difficult to illustrate with clarity and the print head is therefore shown only very schematically in Fig.

4. The print characters are so arranged on the petals or limbs that there are four of the above relatively axially spaced rings or levels of print characters 82, though there may be any number of such levels from two upwards.

As will be evident, the print characters 82 occupy a cylindrical surface which is coaxial with the axis 0-0 of the shaft 1 8. To print a character, the control unit 10 is energised to move the thimble 80 axially up from the illustrated 'park' position into a position in which the level or ring of the characters 82 containing the desired character is at the level of a print position X and to rotate the thimble 80 until the desired character in the level or ring is at the print position X. The foregoing linear and rotational movement steps are preferably carried out simultaneously, for the sake of speed, but could be performed in sequence if so desired. A print hammer 84 is then actuated to cause impact of the selected character against paper 86 entrained around a platen 88 to print the character on the paper.

(The means supporting and actuating the hammer 84 are not shown and may be of conventional form, and, for this purpose, the shaft 1 8 may be hollow if required.) Each subsequently desired character is then indexed to the print position X and printed on the paper 86 in the same manner.

An advantageous feature of the arrangement of Fig. 4 is the fact that the control unit 10 has the 'park' position, i.e. the capacity to move axially to a position in which the thimble 80 does not obscure the last character printed. This facility obviates the need to enable the last character to be viewed by providing a cut-out in the thimble and aligning this with the print position X when printing is not taking place. The absence of such a cutout improves the usage of space, reduces the diameter and inertia of the thimble (the inertia being proportional to the fourth power of the radius) and can reduce manufacturing costs.

Fig. 5 shows how the control unit 10 can be used to drive a robot gripper or manipulator 90. The manipulator 90 comprises a pair of digits 92 having jaws 94 and pivoted at pivot points 96 so that the jaws move towards or away from one another. The pivots 96 are mounted on a hand 1 00 which is rotatably received within an arm 102, for swivelling movement about the axis 104 of the arm, by means of bearings 106. A gaiter 107 is mounted to the digits 92 and hand 100 as shown.

The combined motion drive unit 10 is mounted within the arm 102 and the shaft 1 8 thereof extends into and is fixed within a bore 108 in a member 110 mounted within the hand 100 in such a manner that it can translate but not rotate relative to the hand.

The mounting of the member 110 within the hand 100 may be accomplished, as shown, by rows of ball bearings 11 2 received within axial grooves, or by the provision of splines.

The member 110 is connected to the digits 92, which are in the form of cranks, by links 114 each pivoted to the member 110 at a pivot point 11 6 and to the digit 92 at a pivot point 118.

As will be evident, by energising the unit 10 to cause axial movement of the shaft 1 8 and the member 110 fixed thereto, the digits 92 can be pivoted such that their jaws 94 move towards or away from one another.

Thus, the grasping or gripping of the human hand can be simulated. Further, by rotating the shaft 1 8 by suitably energising the unit 10, the whole hand can be caused to swivel or rotate about the axis 104, thereby also simulating the human wrist action.

Movements of the digits 92 and of the hand 100 can be accomplished by suitably energising the motors of the control unit 10 to drive them to desired positions. In some instances, however, in particular where it is desired to limit the force or torque imparted to objects picked up by the manipulator 90, one may instead or alternatively modify or terminate the action of the control unit 10 by feedback from position, force or torque sensors or the like.

Another application of the combined motion drive unit 10 is in the driving of a tracking or scanning system, i.e. a system for following or looking for something. The item driven by the control unit 10 may be, for example, a television camera, a satellite tracking arial, a radar scanner, an astronomical telescope or camera or a light projector. Such an arrangement is depicted in Figs. 6 and 7 in which an object to be moved by the unit 10 is shown, by way of example, as being a radar scanner 1 30. In a manner which will now be described, the control unit 10 alters both the bearing and elevation of the scanner 1 30.

The scanner 1 30 is pivotally mounted at pivot points 1 34 on a member 1 36 rotatably mounted by bearings 1 38 in a housing 140 for movement about a vertical axis 142.

The shaft 1 8 is fixed in a bore within a member 144 mounted within the member 1 36 so as to be movable along the axis 142 with respect to the member 1 36 but so as not to be rotatable with the member 136. The mounting of the member 144 within the member 1 36 may be accomplished, as shown, by rows of ball bearings 146 received within grooves or by the provision of splines.

A link 148 is pivoted to the member 1 44 at a position 1 50 and to the scanner 1 30 at a position 1 52.

To vary the bearing of the scanner 130, the unit 10 is energised to rotate the shaft 1 8.

Such rotation is transmitted to the member 1 36 via the member 142 and the ball bearing connection arrangements 146. The resultant rotation of the member 1 36 about the axis 142 causes the bearing angle of the scanner to change.

To change the angle of elevation of the scanner 130, the shaft 1 8 is moved axially.

Such movement is transmitted to the scanner 1 30 via the member 142 and the link 148 whereby the scanner pivots about the horizontal axis defined by the pivot points 1 34 to change its angle of elevation.

Fig. 8 schematically represents a simple clutch and/or brake mechanism incorporating the combined motion drive unit 10. A disc 1 60 having thereon friction pads 1 62 is fixedly connected to the shaft 1 8 and a further disc 1 64 is fixed to a tubular shaft 166 in which the shaft 1 8 is loosely received.As will be evident, if the arrangement is functioning as a clutch, the disc 1 60 can be moved axially into contact with the disc 1 64 and the shaft 1 8 rotated whereby the shaft 1 66 is driven by the unit 1 0. If, however, the unit functions simply as a brake to slow movement of the shaft 166, this can be effected by moving the disc 1 60 into contact with the rotating disc 1 64 by axial movement of the shaft 18.

Fig. 9 shows schematically how the combined motion drive unit 10 can be used as a gear change unit or, more precisely, as a variable speed drive/transmission unit. Gears 1 70 and 1 72 are mounted on the shaft 1 8 and further gears 174,176 are mounted on a shaft 1 78 to be driven. To drive the shaft 1 78 at one speed, the shaft 1 8 is moved axially to engage the gears 1 70 and 174, as shown, and the shaft 1 78 is then driven by rotational movement of the shaft 1 8. To rotate the shaft 1 78 at a different speed the shaft 1 8 is extended so that the gears 1 72 and 1 76 are engaged.

Claims (20)

1. A combined motion drive unit comprising a casing, a shaft housed in the casing, first drive means incorporated in the casing and operative to rotate the shaft, and second drive means incorporated in the casing and operative to translate the shaft along its axis, the first and second drive means being such that they can be selectively energised to provide mutually independently controllable axial and rotational motion of the shaft.

2. A drive unit according to claim 1, wherein the first drive means comprises a first motor and the second drive means comprises a second motor,

3. A drive unit according to claim 2, wherein at least one of the motors is an electric motor.

4. A drive unit according to claim 2 or claim 3, wherein at least one of the motors is a stepping motor.

5. A drive unit according to claim 4, wherein each of the motors is a stepping motor and the unit is provided with energisation means operative to energise the motors in such a manner as to cause the shaft to move axially and/or rotationally to any one of a plurality of desired positions.

6. A drive unit according to any one of claims 2 to 5, wherein each of the motors is of a type producing rotary motion and cooperating screw threads are associated with the second motor to convert its rotary motion into a linear motion.

7. A drive unit according to claim 6, wherein a rotor of the first motor is fixed with respect to the shaft whereby energisation of the first motor causes rotation (but not translation) of the shaft, a rotor of the second motor surrounds the shaft and the shaft is attached to such rotor in such a manner as to be movable axially together with the rotor but not rotatable with the rotor, and the co-operating screw threads comprise a first thread fixed with respect to the casing and a second thread fixed with respect to the rotor of the second motor, whereby energisation of the second motor causes translation (but not rotation) of the shaft.

8. A drive unit according to claim 7, wherein the first thread is a female thread and the second thread is a male thread of a tubular lead screw surrounding the shaft and fixed with respect to the rotor of the second motor.

9. A drive unit according to claim 6, wherein the shaft is formed as a lead screw which is threaded at least over a portion of its length extending through rotors of the first and second motors, the rotor of the first motor is connected to the shaft via connection means that will transmit rotary movement of the rotor to the lead screw without preventing axial movement of the lead screw, and the co-operating screw threads comprise the male thread of the lead screw and a female thread on a tubular member screwed on the lead screw and fixed with respect to the rotor of the second motor.

10. A drive unit according to claim 9, wherein the connection means comprises a collar that is fixed with respect to the rotor of the first motor and surrounds the lead screw, and rolling bearing elements housed partly in axial grooves on the surface of the lead screw and partly in axial grooves in the inner surface of the collar.

11. A drive unit according to claim 9 or claim 10, including energisation means operative to (i) drive both rotors in the same direction and in synchronism with one another whereby the co-operating screw threads are stationary with respect to each other and the shaft rotates but does not move axially, and (ii) to hold the rotor of the first motor stationary to prevent shaft rotation and to rotate the rotor of the second motor whereby the cooperating screw threads cause the shaft to move axially.

12. A combined motion drive unit substantially as herein described with reference to Fig.1 of the acompanying drawings.

1 3. A combined motion drive unit substatnially as herein described with reference to Figs. 2 and 3 of the accompanying drawings.

14. A printing device comprising a print head formed from a plurality of elongate flexible elements bearing print characters so disposed that the characters occupy a generally cylindrical surface whereby any selected one of the characters can be brought to a print position by movement of the print head both rotationally about and along the axis of the cylindrical surface, and a drive unit according to any one of the preceding claims, the print head being mounted on the shaft of the drive unit and the shaft being coaxial with said cylindrical surface whereby the drive unit can be used to bring any selected one of the characters to the print position.

1 5. A print device according to claim 14, wherein the drive unit is capable of axially moving the print head to a 'park' position in which the head does not obscure viewing of the last character printed by the print head.

1 6. A printing device substantially as herein described with reference to Fig. 4 of the accompanying drawings.

1 7. A manipulator substantially as herein described with reference to Fig. 5 of the accompanying drawings.

1 8. A scanning and/or tracking arrangement substantially as herein described with reference to Figs. 6 and 7 of the accompanying drawings.

1 9. A clutch and/or brake mechanism substantially as herein described with reference to Fig. 8 of the accompanying drawings.

20. A variable speed drive/transmission arrangement substantially as herein described with reference to Fig. 9 of the accompanying drawings.