End-of-arm tool assembly for a robotic manipulator

Abstract

An end-of-arm tool assembly 16 for a robotic arm (14 figure 1) comprises a housing 102 within which is an actuator 104 comprising two counter-moving components 106, 108 such that both counter-moving c

Description

The present disclosure relates to an end-of-arm tool or gripper assembly for a robotic manipulator. Aspects of the invention relate to the end-of-arm tool assembly and to the robotic manipulator comprising the tool assembly. BACKGROUND Known end-of-arm tool assemblies operate with indirect force control schemes using either a position control scheme, or a force plus position control scheme. In the position control scheme, the respective positions of the tool’s finger assemblies are controlled independently of the gripping force applied at the finger assemblies. In the force plus position control scheme, the respective positions of the finger assemblies are controlled with respect to a force limit. That is, force plus position control schemes do not maintain or adjust the gripping force, but simply limit the maximum force that can be applied at the finger assemblies. The problem with these indirect force control schemes is that they need extra force sensors at the contact areas of the finger assemblies in order to measure gripping force. Also, since the force control is done indirectly through position, even if there is a feedback of the gripping force, the control is prone to instability due to contact modelling errors. Also, most of the tool assemblies in the market are not backdrivable, making them less safe to interact with. Such control schemes are also a source of instability and poor control performance. It is against this background that the invention was devised. SUMMARY Accordingly, there is provided, in one aspect, an end-of-arm tool or gripper assembly for a robotic arm, the tool assembly comprising a housing, an actuator comprising two countermoving components, the actuator being movably mounted within the housing such that both counter-moving components are movable and a linkage assembly comprising two linkage subassemblies, each linkage subassembly being arranged to connect the actuator to a finger assembly, wherein the actuator and the linkage assembly are configured such that one of the linkage subassemblies is driven by one of the counter-moving components and the other of the linkage subassemblies is driven by the other of the counter-moving components. This arrangement is advantageous, firstly, in that it enables the end-of-arm tool assembly to be controlled using a direct force control scheme as opposed to using a position control scheme. When using position control schemes, target positions for finger assemblies are determined based on an item to be manipulated or grasped and the force applied to the item is a function of the target positions. Such control schemes are appropriate for applications in which the items to be manipulated have generally similar or the same characteristics. In other applications, however, such as an online grocery retail operation, having 1,000s or 10,000s of items of varying characteristics (e.g., shape, size, weight, rigidity, coefficient of friction, etc.,), such control schemes are inappropriate as two items of similar sizes might be very different in other respects, and so the force applied to them by the finger assemblies, determined as a function of their respective positions, might be unsuitable. That is, in most instances, the relationship between the applied force and position of the finger assemblies is unknown when using position control schemes. With the present arrangement, however, which lends itself to a direct force control scheme, target positions or any feedback regarding the positions of the finger assemblies is not required. Instead, the output force or torque of the actuator is controlled to match the desired force applied by finger assemblies to the item being manipulated. This is made possible by the novel arrangement of using linkage assembly directly connected to the actuator. The linkage assembly is a low friction transmission device, which, in this instance, is used to convert output force of the actuator to axially reciprocating movement of the finger assemblies. Because it is a low friction transmission device, and in the absence of other transmission mechanisms, such as a gearing arrangement between the actuator and the linkage assembly, the applied force of the finger assemblies is proportional to the force output of the actuator, meaning that the applied force can be accurately mapped with respect to the force output to provide precise direct force control capability without the need for external force measurement. Secondly, because the linkage assembly provides a low friction transmission between the actuator and finger assemblies, the end-of-arm tool assembly is mechanically backdrivable. That is, the finger assemblies can be moved manually, towards or away from each other, to effect movement of the linkage assembly and actuator. This ensures that the end-of-arm tool assembly has a degree of compliance, permitting safe physical interaction with its workspace. Finally, the absence of an intermediate transmission device between the actuator and linkage assembly minimises the “backlash” within the assembly, which could otherwise lead errors in the force applied by the finger assemblies to an item being manipulated. Optionally, the counter-moving components are counter-rotatable and wherein the actuator is rotatably mounted within the housing such that both counter-rotating components are rotatable. In this instance, the actuator might be a motor, having a stator and rotor as the counterrotating components. Conventionally, the stator would be secured to the housing, preventing its rotation relative to the rotor. The arrangement of the current end-of-arm tool assembly, however, allows both the rotor and stator to counter-rotate within the housing to produce equal but opposite torques. This means the output torque produced by the rotation of the stator, instead of being absorbed by housing as would be the case in a conventional arrangement where the stator is secured to the housing, can be used to drive one of the linkage subassemblies, while the output torque of the rotor is used to drive the other of the linkage subassemblies, thereby doubling the effective force applied to the linkage assembly without the use of an intermediate transmission device between the actuator and linkage assembly. Optionally, the counter-rotating components are concentrically arranged about a common rotational axis. Optionally, the tool assembly further comprises a coupler assembly connected to the linkage subassemblies. Optionally, the coupler assembly comprises an elongate guide and a slider coupling the linkage subassemblies, wherein the slider is configured to reciprocate along the guide as the actuator drives the linkage assembly. Optionally, a longitudinal or major axis of the elongate guide is perpendicular to the common rotational axis. Optionally, each linkage subassembly comprises an actuator linkage rotationally coupled to one of the counter-rotating components and pivotally connected to the other linkages of the linkage subassembly. Optionally, the pivotal connections between the actuator linkage and the other linkages of the linkage subassembly are equidistant from the common rotational axis. In another aspect, there is provided a robotic manipulator comprising a tool assembly according to the previous aspect. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a schematic view of a manipulator apparatus for use with the invention; according to an embodiment of the invention; Figure 2 is a cross-sectional plan view of an end-of-arm tool assembly according to an embodiment of the invention for use with the manipulator apparatus of Figure 1, wherein the end-of-arm tool assembly is a closed configuration; Figure 3 is a cross-sectional plan view of the end-of-arm tool assembly of Figure 2 in an open configuration; and, Figure 4 is a cross-sectional side view of the end-of-arm tool assembly of Figure 2. In the drawings, like features are denoted by like reference signs where appropriate. DETAILED DESCRIPTION In the following description, some specific details are included to provide a thorough understanding of the disclosed examples. One skilled in the relevant art, however, will recognise that other examples may be practised without one or more of these specific details, or with other components, materials, etc., and structural changes may be made without departing from the scope of the invention as defined in the appended claims. Moreover, references in the following description to any terms having an implied orientation are not intended to be limiting and refer only to the orientation of the features as shown in the accompanying drawings. In some instances, well-known features or systems, such as processors, sensors, storage devices, network interfaces, fasteners, electrical connectors, and the like are not shown or described in detail to avoid unnecessarily obscuring descriptions of the disclosed embodiment. Unless the context requires otherwise, throughout the specification and the appended claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” Reference throughout this specification to “one”, “an”, or “another” applied to “embodiment”, “example”, means that a particular referent feature, structure, or characteristic described in connection with the embodiment, example, or implementation is included in at least one embodiment, example, or implementation. Thus, the appearances of the phrase “in one embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, examples, or implementations. It should be noted that, as used in this specification and the appended claims, the users forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise. Figure 1 shows an example manipulator apparatus, generally designated by 10. The manipulator apparatus 10 comprises a robotic manipulator 12 including a robotic arm 14, an end effector or end-of-arm tool assembly 16 (hereinafter, “tool assembly 16”) and a motion subsystem 18. The motion subsystem 18 is communicatively coupled to the robotic arm 14 and tool assembly 16, and is configured to cause the robotic arm 14 and tool assembly 16 to move in accordance with actuation commands or control signals issued by a controller 20, which forms part of the manipulator apparatus 10. The robotic arm 14 and tool assembly 16 define a plurality of interconnected parts that are configured to move relative to each other in order to carry out the manipulation of an object, e.g., grasped by the tool assembly 16. Motors and respective gearboxes are provided at junctions between the interconnected parts to enable the relative movement. With reference to Figure 2, the tool assembly 16 comprises a housing 102 and an actuator, generally designated by 104, comprising two counter-moving components 106, 108. The actuator 104 is mounted within the housing 102 such that both counter-moving components 106, 108 can move therein in an opposing manner. That is, the actuator 104 is mounted in the housing 102 so that one of the counter-moving components 106, 108 is able to move in a first direction, while the other of the counter-moving components 106, 108 is arranged to move in a second direction, the second direction being opposite to the first direction. In this example, the actuator 104 is a motor 110 comprising a rotor 106 and a stator 108, which define counter-rotating components concentrically arranged about a common rotational axis 112. Conventionally, the stator 108 would be secured to the housing 102, preventing its rotation relative to the rotor 106. In this example, however, the stator 108 and rotor 106 are rotatably supported within the housing 102 on first and second bearing assemblies 109, 111 (see Figure 4), enabling the stator 108 to rotate within the housing 102 in one of a clockwise or anticlockwise direction while the rotor 106 rotates in the other of a clockwise or anticlockwise direction. The tool assembly 16 further comprises a linkage assembly, generally designated by 114, having two linkage subassemblies 116, 118 directly connected to the actuator 10. The linkage subassemblies 116, 118 function to operatively connect respective finger assemblies 120, 122 to the actuator 104 such that one of the linkage subassemblies 116, 118 is driven by one of the counter-moving components 106, 108 and the other of the linkage subassemblies 116, 118 is driven by the other of the counter-moving components 106, 108. Each of the linkage subassemblies 116, 118 includes an actuator linkage 124, 126, providing a direct connection between respective linkage subassemblies 116, 118 and counter-moving components 106, 108. To that end, each actuator linkage 124, 126 are fixedly coupled to one of the counter-moving components 106, 108, preventing relative movement therebetween, and pivotally connected to the other linkages of their linkage subassembly 116, 118. In the example shown, linkage subassembly 116 is connected to the stator 108 by actuator linkage 124, which is configured to pivot with respect to the other linkages of linkage subassembly 116 about pivotal connection 128. Similarly, linkage subassembly 118 connects to the rotor 106 by actuator linkage 126, which is configured to pivot with respect to the other linkages of linkage subassembly 118 about pivotal connection 130. In order to facilitate a coupled movement of the linkage subassemblies 116, 118, and so the finger assemblies 120, 122, between a closed configuration, as shown in Figure 2, and an open configuration, as shown in Figure 3, the pivotal connections 128, 130 are arranged such that their respective distance from the rotational axis 112 is substantially the same regardless of the positions of the counter-moving components 106, 108. The tool assembly 16 further comprises a coupler assembly 132, providing an interconnection between linkage subassemblies 116, 118. This interconnection establishes a coupled association between the linkage subassemblies 116, 118, ensuring a corresponding movement of the finger assemblies 120, 122. The coupler assembly 132 comprises an elongate guide 134, arranged such that its major axis extends perpendicular with respect to the common rotational axis 112, and a slider 136 connected to the linkage subassemblies 116, 118. The slider 136 is configured to reciprocate along the guide 134 as the actuator 104 drives the linkage assembly 114 between the open and closed configurations.

Claims

1. An end-of-arm tool assembly for a robotic arm, the tool assembly comprising:a housing;5 a motor comprising two counter-rotatable components concentricallyarranged about a common rotational axis, the motor being mounted within the housing such that both counter-rotatable components are rotatable; and,a linkage assembly comprising two linkage subassemblies, each linkage subassembly being arranged to connect the actuator to a finger assembly, wherein10 the motor and the linkage assembly are configured such that one of the linkagesubassemblies is driven by one of the counter-rotatable components and the other of the linkage subassemblies is driven by the other of the counter-rotatable components.152000 C\J2. A tool assembly according to claim 1, further comprising a coupler assembly connected to the linkage subassemblies.

3. A tool assembly according to claim 2, wherein the coupler assembly comprises anelongate guide and a slider coupling the linkage subassemblies, wherein the slider is configured to reciprocate along the guide as the motor drives the linkage assembly.

4. A tool assembly according to any preceding claim, wherein a longitudinal axis of the25 elongate guide is perpendicular to the common rotational axis.

5. A tool assembly according to any preceding claim, wherein each linkage subassembly comprises a motor linkage rotationally coupled to one of the counterrotatable components and pivotally connected to the other linkages of the linkage30 subassembly.

6. A tool assembly according to claim 7 when dependent on claim 3 or any claim dependent thereon, wherein the pivotal connections between the motor linkage and the other linkages of the linkage subassembly are equidistant from the common35 rotational axis.

7. A robotic manipulator comprising a tool assembly according to any preceding claim.

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