WO1996026044A2

WO1996026044A2 - Material handling

Info

Publication number: WO1996026044A2
Application number: PCT/GB1996/000384
Authority: WO
Inventors: John Wallace
Original assignee: Clansman Dynamics Limited
Priority date: 1995-02-21
Filing date: 1996-02-21
Publication date: 1996-08-29
Also published as: WO1996026044A3; AU4884096A

Abstract

A control arm (40) for controlling the position of a slave arm (10) of a material handling apparatus has an electric force feedback system for enhancing the 'feel' of the control arm. The control arm is supported for substantial linear movement such that it can be operated by the operator whilst resting the weight of his or her arm on the control arm. The slave arm is fitted with a combined breaker/handling tool (20) having a support member (21), a breaking member (24) movable relative to the support member and a movable gripping member (25).

Description

MATERIAL HANDLING

This invention relates to material handling and particularly, but not exclusively, to a manipulator for use in the foundry industry.

Runners and risers have hitherto been removed from castings by powered hammers, shears and expansion breaker and wedge systems. For the latter, lugs must be cast into the casting system for the expansion breaker system and wedges to react against. Shears do not provide satisfactory cutting of runners and risers and are prone to rapid wear. Breaking machines that operate on hydraulic excavators are too bulky and heavy for use with a manipulator. Furthermore, these known systems require separate handling and breaking apparatus.

Some manually operated manipulators are arranged with a hydraulic force feedback system to provide an operator of a controlling arm with a "feel" for the actions and forces acting on the slave arm. Although such systems facilitate manual control of the slave arm, existing hydraulic force feedback systems are imprecise and are fatiguing to operate. According to a first aspect, the present invention provides material handling apparatus comprising a user operable control arm for controlling a position of a slave arm characterised in that an electrical force feedback motor is arranged to apply a reactive force to the control arm.

Preferably, the action of the force feedback motor is controlled by a force feedback control system. The force feedback control system may provide an output to the force feedback motor as a transfer function of an input. The input may be provided by an error signal derived from a difference in position between the actual position of the slave arm and the position to which the slave arm has been commanded to move by the control arm. The input may be derived from a speed or an acceleration or from a difference in a speed or acceleration of the control arm and/or the slave arm.

The transfer function may be programmable or otherwise changeable so that the system may be modified to operate with a modified transfer function.

The system preferably provides a variable, or non- linear, force feedback on the control arm in response to the input to the force feedback control system. This may provide an operator of the control arm with an appreciation of the actual position of the slave arm. Preferably, if the operator attempts to move the control arm to a position more quickly than the slave arm can respond, a lead between the position of the control arm and the position of the slave arm will induce a force feedback on the control arm through the force feedback motor. This may facilitate the operator's perception of the actual position of the slave arm and encourage him or her when moving the control arm to maintain a relatively small lead between the control arm position and the slave arm position.

One disadvantage of known, hydraulic force feedback systems is that they produce a force that the operator has to overcome even when the machine is driven correctly. This is fatiguing but can be overcome by means of the present invention.

The transfer function may have a first response section at which a small difference between the position of the control arm and the actual position of the slave arm induces little or no reactive force at the force feedback motor. The function may have a second response section at which a change in the difference between the position of the control arm and the position of the slave arm induces a substantially proportional reactive force at the force feedback motor. The function may have a third response section at which a difference between the position of the control arm and the position of the slave arm induces a substantially proportional reactive force of greater magnitude at the force feedback motor. For example, the transfer function f(x) may be modelled as:

where r,s,t,u,a and b are constants, t<r and |s| > |u| , and where x is the input to the force feedback control system. Thus, the force feedback can be shaped so that an operator experiences different levels of force for a given difference between master and slave positions.

Furthermore, the characteristics of the system can be easily modified by changing electrical components or reprogramming the transfer function. The present system also alleviates the need for having any hydraulic components (which can leak) in the control cabin.

The control arm may be adapted to move in two or more directions to control the position of the slave arm. Preferably, a force feedback motor controlled by the force feedback control system or by respective force feedback control systems is associated with each direction of movement of the control arm.

According to a second aspect, the present invention provides a control arm adapted to control a position of a slave arm in which the control arm is supported for substantially linear movement.

The control arm may also be rotatable about an axis of rotation.

Support of the control arm for linear movement may allow an operator of the control arm to rest his or her arm upon the control arm during use. It may alleviate the necessity of the operator supporting the weight, or part of the weight., of the control arm during use.

Position of the control arm in respect of one or more of its directions of movement may be sensed by a sensor, for example, a potentiometer. One or more rotary sensors may be used, and, one or more pulleys and belts may be used to translate a linear motion of the control arm to a rotary motion for movement of an associated rotary sensor.

According to a third aspect, the present invention provides material handling apparatus comprising an articulated slave arm characterised in that beyond a preset angle of articulation a force limitation system is activated to limit the force with which the slave arm is advanced.

According to a fourth aspect, the present invention provides a tool comprising a support member, a breaking member movable relative to the support member and a movable gripping member.

The tool may be adapted for fitment to a material handling apparatus. It may be fitted to a robotic arm, a manipulator or a crane.

Preferably, the breaking member is arranged at a first side of the support member and the gripping member is arranged at a second side of the support member. The breaking member and the gripping member may be arranged at opposite sides of the support member.

The breaking member and/or the gripping member may be pivotally attached to the support member and may be operated by an actuator or by respective actuators; they may be rotatable about respective pivots to move respective ends toward or away from the support member. The actuator or actuators may be hydraulically or pneumatically operated.

The support member may comprise a pair of spaced prongs. A gap may separate the prongs. Each prong may, in cross-section, have a raised contact portion, the raised contact portions being separated by a recess or trough.

The breaking member may have a single prong adapted to move between the two prongs of the support member. The breaking member prong may be profiled to facilitate its cooperation with the support member. It may taper towards a contact portion arranged opposite the support member. The contact portion may be arranged to move between the prongs of the support member; it may be arranged to move into the trough or recess between the prongs and it may move into the gap provided between the prongs.

A member to be broken may be arranged to contact the contact portions of the breaking member and of the prongs of the support member and may then be broken by relative movement between the breaking member and the support member.

The gripping member may be profiled to facilitate gripping of a member. It may comprise an arm having a pair of angularly arranged portions. An object to be gripped may be received between the support member and the angularly spaced portions.

The tool may be adapted for attachment to a remotely controllable arm, for example, a robotic arm.

According to a fifth aspect, the present invention provides a controllable arm of a material handling apparatus fitted with a tool in accordance with the first aspect of the invention.

The invention will now be described, by way of example only, with reference to the accompanying drawings of which:

Fig. 1 is a side view of an articulated slave arm of a material handling apparatus incorporating a number of aspects of the present invention; Fig. 2 is a side view of a combined breaker and handling tool which may be fitted to the articulated arm; Fig. 3 is a sectional view taken along line 3-3 of Fig. 2; Fig. 4 is a perspective view of a control cabin; Fig. 5 is a side view of a control arm; Fig. 6 is a schematic control diagram; Fig. 7 is a annotated version of Fig.6; Fig. 8 is a schematic side view of the slave arm in a different position.

The articulated slave arm 10 of Fig. 1 has a combined breaker and handling tool 20 mounted at one end. The slave arm forms part of a manipulator for use in handling castings and breaking runners and risers in a foundry.

The tool 20 is shown in more detail in Fig. 2 and Fig. 3. The combined breaking and handling tool has a central support 21 comprising a pair of spaced fingers 22, 23 with a breaking member 24 and handling member 25 on opposite sides. The breaker member is pivoted with respect to the support 21 and is moveable by means of a hydraulic actuator.26. A member to be broken is arranged between a contact portion 27 of the breaker 24 and contact portions 28 of the support 21. The hydraulic actuator 26 can move the breaker 24 between spaced fingers 22, 23 of the support 21 to snap the member to be broken. Parts that are in contact with the member to be broken are made of wear-resistant high alloy steels and are quickly detachable.

The handling member 25 is also pivoted with respect to the support member 21 and is moveable by means of a hydraulic actuator 29.

Alternatively, the breaking arrangement may comprise a fixed, single prong and a moving double prong.

The hydraulic circuit includes a regeneration circuit to facilitate rapid movements. In use, an operator presses a trigger to open the breaking finger 24. Once the tool has been manipulated to arrange a member to be broken between the breaking finger 24 and the support 21, the operator then actuates the breaking mechanism which forces the breaking finger 24 to break the member against the double fingers 22, 23 of the support 21. The operator can then use the gripper finger 25 to grip an item against the support 21 for subsequent manipulation.

The same tool 20 can thus be used to grip and manipulate a casting and to break the runners and risers.

Referring now to Fig. 4 and Fig. 5, these show a control arm 40 housed within a control station or cabin 41. The control arm 40 is arranged such that an operator sitting in chair 42 can operate the control arm 40 whilst resting his or her arm on the control arm. The control arm thus supports the operator's arm and minimises operator fatigue.

The control cabin 41 may be adjacent to or remote from the slave arm. Part of the control circuitry is housed in a cabinet 43 within the control cabin 41. This includes a 64 channel build-in diagnostic. The operator is also provided with a visual display 44 which provides a safe start-up facility.

When operating the system, an operator rests his arm on the top surface 45 of control arm 44. The control arm 40 is supported for substantial linear movement backwards and forwards and is also pivoted about bearing 46. The control arm has an additional controller 47 in the form of a hand grip which is rotatable to the left and to the right by the operator using his or her wrist whilst keeping his or her arm supported on the top surface 45 of the control arm 40.

The linear position of the control arm 40 is sensed by potentiometer 48 driven by toothed belt 49. The rotational position of the control arm 40 is sensed by potentiometer 50 driven by toothed drive belt 51. A corresponding potentiometer (not shown) senses the rotational position of controller 47.

The position to which the operator moves the control arm 40 is used to control the position of the slave arm 10.

A force feedback system, which is illustrated in Fig. 6, controls force feedback motors 52, 53. This varying signal/current produces varying torques in the force feedback motors 52, 53 which are sensed by the operator. To minimise the effort needed to operate the control arm 40, the operator must keep the control arm 40 and the slave arm synchronised.

The combined rotary/linear geometry of the control arm 40 is designed to allow the operator to rest the complete weight of his or her arm on the control arm as he or she operates the machine.

The controller 47 is mounted on the third axis along the linear axis of the control arm 40.

Fig. 6 shows a schematic control diagram of the force feedback system. This embodiment has a first control circuit 61 for controlling the force feedback of force feedback motor 53 associated with vertical movement of the slave arm 10 and a second control circuit 62 for controlling the force feedback of force feedback motor 52 associated with horizontal movement of the slave arm 10.

The first control circuit uses an error signal 63 derived from a vertical command signal 64 from potentiometer 50 and a position feedback potentiometer 65 which measures the vertical position of the slave arm 10. An acceleration control 66 and voltage to current convertor 67 is used to control a servovalve 68 to control the position of the slave arm. The error signal 63 is also fed via a transfer function 69 and power amplifier 70 to control force feedback motor 51. The transfer function 69 is fed with an additional input from external sensors 71.

The second control circuit operates in a similar way. An error signal 83 is derived from a horizontal command signal 84 from potentiometer 48 and a position feedback potentiometer 85 which measures the horizontal position of the slave arm 10. An acceleration control 86 and voltage to current convertor 87 is used to control a servovalve 88 to control the position of the slave arm. The error signal 83 is also fed via a transfer function 89 and power amplifier 90 to control force feedback motor 52. The transfer function 89 is fed with an additional input from external sensors 91.

The two circuits are linked via modulus and shaping circuitry 92.

Fig. 8 shows a schematic view of the articulated slave arm at an angle of extension α. The arm is moved by a hydraulic cylinder 101. Once the centre of gravity of the arm 100 has moved forwards beyond its highest position, the force causing the arm to move further forwards will be a combination of the force of hydraulic cylinder 101 and the gravitational weight of the arm. In order to limit this forward force (and reduce the risk of damaging equipment in the case of collision of the arm 100) a sensor (not shown) is used to detect when the arm 100 extends beyond a pre-set extension angle α. This may be a potentiometer. When angle α is exceeded and the arm 100 is moved forward the control system activates a force limitation hydraulic circuit to reduce the pressure in the hydraulic cylinder 101.

Claims

1. Material handling apparatus comprising a user operable control arm for controlling a position of a slave arm characterised in that an electrical force feedback motor is arranged to apply a reactive force to the control arm.

2. Apparatus in accordance with Claim 1 in which the action of the force feedback motor is controlled by a force feedback control system which provides an output to the force feedback motor as a transfer function of an input.

3. Apparatus in accordance with Claim 2 in which the input to the force feedback control system is derived from a difference in position between the actual position of the slave arm and the position to which the slave arm has been commanded to move by the control arm.

4. Apparatus in accordance with Claim 1 or Claim 2 in which the transfer function is programmable.

5. Apparatus in accordance with any one of Claims 2 to 4 in which the force feedback on the control arm is substantially non-linear in respect of the input.

6. A force feedback system adapted for use with apparatus according to any one of Claim 1 to 5.

7. A control arm adapted to control a position of a slave arm characterised in that the control arm is supported for substantially linear movement.

8. A control arm in accordance with Claim 7 provided with a rotary controller for controlling a position of a slave arm in which the rotary controller is a hand- held actuator rotatable by an operator by means of movement of the operator's wrist whilst the operator's arm is supported on the control arm.

9. A control arm in accordance with Claim 7 or Claim 8 in which the control arm is rotatable about an axis of rotation to control a position to the slave arm.

10. Apparatus in accordance with any one of Claims 1 to 5 comprising a control arm in accordance with any one of Claim 7 to 9.

11. Material handling apparatus comprising an articulated slave arm characterised in that beyond a present angle of articulation a force limitation system is activated to limit the force with which the slave arm is advanced.

12. Apparatus in accordance with Claim 11 and in accordance with any one of Claims 1, 2, 3, 4, 5 or 10.

13. A tool for a material handling apparatus comprising a support member, a breaking member movable relative to the support member and a movable gripping member.

14. A tool in accordance with Claim 13 in which the breaking member is arranged at a first side of the support member and. the gripping member is arranged at a second side of the support member.

15. A tool in accordance with Claim 14 in which the gripping member and the breaking member are arranged at opposite sides of the support member.

16. A tool in accordance with any one of Claims 13 to 15 in which the breaking member and the gripping member are pivotally attached to the support member and are operated by means of respective actuators.

17. A tool in accordance with any one of Claims 13 to 16 in which the support member comprises a pair of spaced prongs.

18. A tool in accordance with Claim 17 in which each prong has, in cross-section, a raised contact portion, the raised contact portions being separated by a recess or trough.

19. A tool in accordance with any one of Claim 17 to 18 in which the breaking member comprises an single prong adapted to move between the two prongs of the support member.

20. A tool in accordance with Claim 19 in which the breaking member prong tapers towards a contact portion arranged opposite the support member.

21. A tool in accordance with Claim 20 in which a member to be broken is adapted to be arranged to contact the contact portions of the breaking member and of the prongs of the support member and to be broken by bending and snapping between the breaking member and the support member.

22. A tool in accordance with any one of Claims 13 to 21 in which the gripping member comprises an arm having a pair of angularly spaced portions.

23. A material handling apparatus fitted with a tool in accordance with any one of Claims 13 to 22.

24. Apparatus in accordance with Claim 23 and in accordance with any one of Claims 1 to 5, 11 or 12.

25. Apparatus substantially as hereinbefore described with reference to any one of the accompanying drawings.