WO1986006673A1

WO1986006673A1 - Robotic arm

Info

Publication number: WO1986006673A1
Application number: PCT/GB1986/000262
Authority: WO
Inventors: Timothy John Jones
Original assignee: UNIVERSAL MACHINE INTELLIGENCE Ltd
Current assignee: UNIVERSAL MACHINE INTELLIGENCE Ltd
Priority date: 1985-05-13
Filing date: 1986-05-13
Publication date: 1986-11-20
Anticipated expiration: 1987-11-13
Also published as: GB8512056D0; JPS62502844A; AU5815486A

Abstract

A robotic arm comprises a shoulder (1), first and second arm sections (2, 3) and an output member (4) intended to carry a wrist and gripper (80). Three independently operable drive mechanisms, each including an electric motor, gearbox and two stage system of pulleys and belts, are provided for rotating the first arm section about axis (A), rotating the second arm section about axis (B) and rotating the output member about axis (C). The drive mechanisms are so arranged that the wrist and gripper can be driven along a radial direction (A - C) by energising the first and second motors at equal speeds, and energising the second motor causes rotation of the output member to maintain the wrist and gripper (80) in constant angular orientation with respect to the radial direction (A - C).

Description

ROBOTIC ARM

This invention relates to a robotic arm or manipulator. In particular it is concerned with a robotic arm of the form comprising a shoulder section, a first arm section connected to the shoulder section for rotation about a first pivot axis, a second arm section connected to the first arm section for rotation

• about a second pivot axis, an output member connected to the second arm section for rotation about a third axis, the first, second and third axes being parallel to each other and the first and third axes being spaced from the second axis by equal distances, and drive means for rotating the first arm section, the second arm section and the output member about the first, second and third axes, respectively. The invention has for its aim to provide a robotic arm of the construction set out above which enables accurate control of a device, e_*g. a gripper carried.by the output member, while permitting a wide range of movement of the device, simple control of the drive means and economic manufacture. A robotic arm according to the invention is characterised in that the drive means includes first drive means for rotating the first arm section about the first axis, second drive means for rotating the second arm about the second axis, and third drive means for rotating the output member about the third axis, the first, second and third drive means being operable independently of each other and being so arranged that the output member can be driven radially of the first axis by operation of the first and second drive means at equal speeds, and operation of the second drive means causes also the output member to be rotated about the third axis through an angle equal to half the angle through which the second arm section is rotated about the second axis. The arm of the invention can be used to advantage in conjunction with the robotic wrist and gripper assembly described in International Patent Application No. PCT/GB86/00123, which will be mounted on the output member of the arm, and with the linear guideway and carriage assembly described in International Patent Application No. PCT/GB86/001*_8, the shoulder section of the arm^* being fastened to the carriage for vertical adjustment of the arm. The arm, especially when in combination with these assemblies, is suitable for use either on a mobile robot or mounted on a stationary base.

In a preferred embodiment of the robotic arm, the first, second and third drive means comprise respect¬ ive electric motors, the first motor being carried by the shoulder section and the second and third motors being carried by the first arm section. Each motor drives a pulley through a gearbox and a system of belts and pulleys providing further gear reduction. The latter system enables standard gearboxes to be used by reducing backlash, e.g. from about 2 for such a gearbox to about 0.05°, whereby costs are kept down but accurate control is still possible to within less than one millimetre.

The invention will be clearly understood from the following detailed description which is given by way of example and with reference to the accompanying drawings, in which:-

Figure 1 is a section through a robotic arm embodying the invention; Figure 2 is an end view of the arm;

Figure 3 s a plan view of the first arm section, some parts having been omitted in the interest of clarity; and

Figures k and 5 are schematic plan views of the arm illustrating operation thereof.

The robotic arm, illustrated in detail in Figures 1 - 3_ι comprises a shoulder section 1 adapted to be mounted on a carriage for vertical movement of the arm, a first or upper arm section 2 connected to the section 1 for rotation about a vertical axis A, a second or lower arm section 3 connected to the upper section 2 for rotation about a vertical axis B, and an^" output member journalled in the lower arm section 3 for rotation about a vertical axis C, the length of the upper arm 2 between the axes A and B being equal to the length of the lower arm 3 between the axes B and C.

The shoulder section 1 includes a support frame 10 including a horizontal platform 11 in which is fixed the upper end of a vertical tubular spindle 12 defining axis A. Also mounted on the platform 11 are a first electric drive motor l with its encoder 15 and gear¬ box l6, and an eccentric spindle 17 carrying freely rotatable combined pulleys 18, 19- One toothed belt 21 is trained around the pulley 18 and a drive pulley 22 provided on the output shaft of the gearbox 16. A second toothed belt 23 is trained around pulley 19 and a driven pulley 2k journalled on the spindle 12. The spindle 17 is normally held fixed in the boss 25 on platform 11 by a clamping screw 26, but after loosen- ing this screw the eccentric spindle can be rotated for adjusting the tension in belt 23- For adjusting the tension in belt 21, a mounting plate supporting motor l4 has slots through which screws 13 pass so that by moving the motor the distance between pulleys 18 and 20 can be varied to obtain the required tension in the belt

23.

The lower end of spindle 12 is supported by a second platform 27 of the support frame 10, ^"and the upper arm 2 comprises a moulding 28 journalled on the spindle 12 between the platforms 11, 27 by bearings 29. The driven pulley 2k is fixed to the moulding 28 by screws 30 so that energising the motor lk causes the upper arm 2 to be rotated about axis A. The rotation of upper arm 2 is limited e.g. to l8θ° by a semi-circular groove 31 formed in the bottom of moulding 28 and in which engages a stop pin 32 fixed to platform 27_*

A vertical tubular spindle 35 defining axis B is journalled in the moulding 28 at the end remote from spindle 12 by bearings 36 and has a driven pulley 37 fast with its upper end. For driving pulley 37 a second electric motor 38 together with its encoder 39. gearbox kO and mounting plate kl are carried on the moulding and fixed by screws k2. Combined pulleys 43» kk are freely rotatable on an eccentric spindle 45 fixed by a clamping screw 46 in a boss of moulding 28, a first toothed belt 7 being trained around pulley 43 and a driving pulley 49 fitted to the output shaft of the gearbox 40, and a second toothed belt 48 being trained around pulleys 44 and 37_* The tension in belts 47, 48 is adjustable in the same way as belts 21, 23_» that is the eccentric spindle 45 being rotatable after releasing the clamp screw 46 to adjust the tension in belt 48, and the mounting plate 4l for the motor 38 having slots for the screws 42 to allow the motor to be moved to adjust the tension in belt 47• The lower arm 3 is formed by a moulding 50 -and is fixed to the lower end of spindle 35 by grubscrews 51 provided in a sleeve 52 fitted in the moulding 50. Thus, energising motor 38, through the gearbox 4θ and system of pulleys and belts causes the spindle 35 and hence the lower arm 3 to be rotated about axis B. The gear ratio between motor 38 and spindle 35 is twice that between motor 14 and the pulley 24, this breing conveniently achieved by the pulleys 49, 43, 44 being the same as pulleys 22, l8, 19 respectively, and pulley 35 having half the number of teeth of the pulley 24. As explained below, this arrangement allows the output member 4 to be driven in a direction radial to axis A by energising the motors 14, 38 to run at equal speeds in opposite directions. As a result, simple summation and subtraction, of position counts from the motor encoders can d fine arm motion in polar coordinates easily, with the minimum of software overhead.

Rotation of the lower arm 3 is limited to an angle of about 330 by a stop finger 56 fixed to the upper arm abutting a stop formed by a web 57 of the moulding 50. The finger 5 can be fitted in either of the two positions shown in Figure 3_ι enabling the lower arm to be turned either clockwise or counter clockwise about axis B to a position directly below upper arm 2, as shown in dashed line in Figure 1. This position of the lower arm is convenient for stowage and by allowing the lower arm to be turned selectively in either direction to that position is of advantage where a pair of arms are to be .mounted on either side of a mobile robot. The output member 4 consists of a plate 60 carried on a spindle 6l journalled by bearings 62 in the moulding 50 for rotation about axis C. Fast with the spindle is a pulley 63. For driving the pulley 63 a third electric motor 64 is provided and is carried by the upper arm 2. The motor 64, ^"its encoder 6 and gearbox 66 are supported on a mounting plate 67 fastened to the moulding 28 by screws 68. Combined pulleys 69, 70 are freely rotatable on the spindle 35_» and one toothed belt 72 is trained around a drive pulley 71 fitted to the output shaft of the gearbox 66 and pulley 69, and another toothed belt 73 is trained around pulleys 63 and 70. The ratio of the numbers of teeth of the pulleys 63 and 70 is 2:1, which means that if motor 64 remains stationary and motor 38 is energised, the output member 4 will be rotated about "axis C through an angle which is half that through which the lower arm is rotated about axis B. As a consequence the orientation of a wrist and gripper carried by member 4, will remain fixed with respect to the direction A-C, as explained below.

The rotati'on of. the output member about axis C is limited e.g. to l8θ° by a stop 75 on the plate 60 engaging in a semi-circular groove in the underside of the mould- ing 50.

With the three independently operable motors the position and orientation of a device, in particular a wrist and gripper, carried by the output member 4 are widely variable within the horizontal plane. The use of the two stage pulley and belt transmissions to provide gear reduction enables the use of standard gearboxes 16, 40 , 66 whereby manufacturing costs are kept down without forfeiture of accurate control. Operation of the arm to produce radial movement is especially convenient, as now explained with reference to Figures 4 and 5« To adjust the wrist and gripper 80 shown attached to the output member along a radial direction Y-Y from the position aligned along the X axis, through the position shown in dashed line and to that shown in full line in Figure 4, the motors l4 and 38 are energised to rotate at the same speed but in opposite directions. As the upper arm 2 turns clockwise about axis A through the angle P, the lower arm 3 turns counter clockwise about axis B through an angle relative to the upper arm, and since the gear ratios of the respective transmissions are 2:1, Q = 2P and axis C moves along a rectilinear path radial to axis A. Furthermore, assuming motor 64 remains stationary, the output member 4 and -hence the wrist and gripper 80, will be rotated about axis C through an angle R and because the pulleys 63, 70 have a gear ratio also 2:1, R = Q/2 = P with the result that the wrist and gripper 8θ maintains constant angular orientation as it moves along the radial path.

In Figure 5 there is shown movement of the arm produced by energising the motor 38 only. The upper arm

2 remains stationary. The lower arm is rotated about axis B by an angle and once again due to the gear ratio of pulleys 63, 70, the wrist and gripper is rotated about n axis C through an angle /2. In the initial and final positions, and throughout the arm movement the angular orientation of the wrist and gripper relative to a radial line intersecting axes A and C remains constant. By approaching objects with the gripper pointing along any radial line from pivot axis A, no energisation of motor 64 is required, and software for controlling manipulation of the arm is simplified.

Claims

CLAIMS :

1. A robotic arm comprising a shoulder section (l), a first arm section (2) connected to the shoulder section for rotation about a first pivot axis (A) , a second arm section (3) connected to the first arm section for rotation about a second axis (B) , an output member (4) connected to the second arm section for rotation about a third axis (C), the first, second and third axes (A-C) being parallel to each other^* and the first and third axes (A, C) being spaced from the second axis (B) by equal distances, and drive means for rotating the first and second arm sections and the output member about the first, second and third axes, respectively, characterised in that the drive means includes first drive means (l4, l6, 18 - 24) for rotating the first arm section (2) about the first axis (A) , second drive means (37. 38, 40, 43, 44, 47 - 49) for rotating the second arm section (3) about the second axis (B) and third drive means (63, 64, 66, 70 - 73) for rotating the out¬ put member (4) about the third axis (C), the first, second and third drive means being operable independently of each other and being so arranged that the output member (4) can be driven radially of the first axis (A) by operation of the first and second drive means at equal speeds, and operation of the second drive means also causes the output member (4) to be rotated about the third axis (C) through an angle ( /2) equal to half the angle (Q) through which the second arm section (3) is rotated about the second axis (B) .

2. An arm as claimed in claim 1, wherein the first, second and third drive means comprise respective electric motors (14, 38, 64).

3. An arm as claimed in claim 2, wherein the first electric motor (l4) is supported by the shoulder section (l) and the second and third electric motors (38, 64) are supported by the first arm section (2).

4. An arm as claimed in claim 2 or 3, wherein each electric motor (l4, 38, 64) is coupled to drive a respective pulley (24, 37, 63) through a gearbox (16, 4θ, 66) and a gear reducing transmission system of pulleys and belts.

5. An arm as claimed in claim 4, wherein the trans¬ mission system associated with the first motor (l4) and/or the second motor (38) includes combined pulleys (l8 - 19_» 3 - 44) carried on a shaft ( 17, 5) which is adjustable to vary the tension in the belts trained around the pulleys.

6. n arm as claimed in claim 5_. wherein the shaft is an eccentric spindle ( 17 , 45) and is rotatable to adjust the belt tension., clamping means (26, 46) being provided for retaining the spindle in the adjusted position, and the combined pulleys (18 - 19_» 43 - 44) being freely rotatable on the spindle.

7. _n arm as claimed in any one of claims 4 to 6, wherein the first motor (14) and/or the second motor (38) and the associated gearbox ( l6 , 40) are mounted to permit positional adjustment thereof for adjusting tension in a belt (21, 47.) trained around a pulley (22, 49) driven by the output shaft of the gearbox.

8. A_n arm as claimed in any one of claims 1 to 7_. wherein the second arm section (3) is fast with a spindle (35) journalled in the first arm section (2) and defining - 10 -

the second axis (B) , the spindle being coupled to the second drive means to be rotated thereby, and the third drive means includes a pulley (70) freely rotatable on the spindle, a further pulley (63) fast with the output member (4) and a belt (72) trained around said pulleys, the gear ratio of the first pulley to the further pulley being 2:1.

9. An arm as claimed in any one of claims 1 to 8, wherein the second arm section (3) is movable to a position beneath the first arm section with the first and third axes (A, C) aligned.

10. An arm as claimed in claim 9_» wherein rotation of the second arm section (3) about the second axis (B) is limited to an angle less than 360 by stop means (56), the position of the stop means being changeable to enable the second arm section to be rotatable selectively either in the clockwise or the counter clockwise to said position underlying the upper arm section.

11. An arm as claimed in any of claims 1 to 10, where¬ in the first arm section comprises a moulding (28) journalled on a spindle (12) supported by the shoulder section and defining the first axis (A), a member (24) driven by the first drive means being fastened to the moulding for rotating the moulding about the spindle (12).