Patent Application
20240408771
The present disclosure relates to a gripper assembly for a robotic manipulator. Aspects of the invention relate to the gripper assembly and to the robotic manipulator comprising the gripper assembly.
Known robotic grippers 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 gripper'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 grippers 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 an aim of the present invention to address one or more of the disadvantages associated with known robotic grippers.
Accordingly, there is provided, in a first aspect, a gripper assembly for a robotic manipulator, the gripper assembly comprising first and second finger assemblies, a ball screw assembly comprising a first ball screw nut connected to the first finger assembly and a ball screw shaft comprising a first section upon which the first ball screw nut is movably mounted, the ball screw shaft being rotatable about its longitudinal axis, and an actuator directly connected to the ball screw shaft and configured to rotate the ball screw shaft about its longitudinal axis, wherein the ball screw nut and ball screw shaft are configured to move the first finger assembly in a direction of the second finger assembly when the ball screw shaft is rotated in one of a clockwise or anticlockwise direction and to move the first finger assembly in a direction away from the second finger assembly when the ball screw shaft is rotated in the other of the clockwise or anticlockwise directions.
This arrangement is advantageous, firstly, in that it enables the gripper 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 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 a ball screw actuator assembly that includes a direct connection between the actuator and the ball screw shaft to move the finger assemblies. The ball screw actuator assembly is a low friction transmission device, which, in this instance, is used to convert output torque 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 ball screw shaft, the applied force of the finger assemblies is proportional to the torque output of the actuator, meaning that the applied force can be accurately mapped with respect to the torque output to provide precise direct force control capability without the need for external force measurement.
Secondly, because the ball screw actuator assembly provides a low friction transmission between the actuator and finger assemblies the gripper assembly is mechanically backdrivable. That is, the finger assemblies can be moved manually, towards or away from each other, to effect rotation of the ball screw shaft. This ensures that the gripper assembly has a degree of compliance, permitting safe physical interaction with its workspace.
Finally, the ball screw actuator assembly can be preloaded to reduce any clearances between the raceways of the first and second ball screw nuts and the first and second sections of the ball screw shaft, minimising the “axial play” or “backlash” within the assembly, which could otherwise lead errors in the force applied by the finger assemblies to an item being manipulated.
Optionally, the gripper assembly further comprises one or more guide rails, a first carriage assembly movably mounted to the one or more guide rails and a first support assembly configured to connect the first ball screw nut and the first finger assembly to the carriage assembly. The one or more guide rails guide the movement of the first finger assembly and prevent the first ball screw nut from rotating when the ball screw shaft is rotated, fixing the rotational position of the first ball screw nut.
Optionally, the first support assembly is configured to provide a rigid connection between the first finger assembly and the first carriage assembly and a movable connection between the first ball screw nut and the first carriage assembly. This configuration isolates the ball screw actuator assembly from any forces applied to the gripper assembly as a result of manipulating an item and transfers them to the first carriage assembly and the one or more guide rails. In particular, it ensures that any radial forces are not brought to bear on the ball screw shaft, which could bend the ball screw shaft and consequently increase the friction between the ball screws and ball screw shaft.
Optionally, the ball screw actuator assembly further comprises a second ball screw nut connected to the second finger assembly and wherein the ball screw shaft further comprises a second section upon which the second ball screw nut is movably mounted and wherein the first and second ball screw nuts and the ball screw shaft are configured to move the first and second finger assemblies towards each other when the ball screw shaft is rotated in one of the clockwise or anticlockwise directions and to move the first and second finger assemblies away from each other when the ball screw shaft is rotated in the other of the clockwise or anticlockwise directions. This configuration provides two opposed movable finger assemblies, offering a great range of positions.
Optionally, the gripper assembly further comprises a second carriage assembly movably mounted to the one or more guide rails and a second support assembly configured to connect the second ball screw nut and the second finger assembly to the second carriage assembly. This arrangement prevents the second ball screw nut from rotating when the ball screw shaft is rotated, fixing the rotational position of the second ball screw nut.
Optionally, the second support assembly is configured to provide a rigid connection between the second finger assembly and the second carriage assembly and a movable connection between the second ball screw nut and the second carriage assembly. This arrangement, in particular, isolates the ball screw shaft from any radial loads produced during the manipulation of an item.
Optionally, the one or more guide rails comprises two guide rails, each guide rails of the two guide rails being positioned either side of the ball screw shaft. This arrangement provides a uniform force distribution across the gripper assembly when manipulating an item.
Optionally, the actuator is located between the first and second sections of the ball screw shaft. This arrangement provides a more uniform rotation of the ball screw shaft, limiting any torsional movement experienced by the shaft.
Alternatively, the actuator is located at one end of the ball screw shaft.
Optionally, the first section of the ball screw shaft comprises one of a right-or left-hand helical raceway and the second section of the ball screw shaft comprises the other of the right-or left-hand helical raceways.
Optionally, the ball screw actuator assembly further comprises a second ball screw nut connected to the second finger assembly, a second ball screw shaft comprising a section upon which the second ball screw nut is movably mounted, the second ball screw shaft being rotatable about its longitudinal axis and a second actuator directly connected to the second ball screw shaft and configured to rotate the second ball screw shaft about its longitudinal axis, wherein the second ball screw nut and second ball screw shaft are configured to move the second finger assembly in a direction of the first finger assembly when the second ball screw shaft is rotated in one of the clockwise or anticlockwise directions and to move the second finger assembly in a direction away from the first finger assembly when the second ball screw shaft is rotated in the other of the clockwise or anticlockwise directions.
According to a second aspect, there is provided a robotic manipulator comprising a gripper assembly according to the first aspect.
According to a third aspect, there is provided a manipulator apparatus comprising a robotic manipulator according to the second aspect.
These and other aspects of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:
In the drawings, like features are denoted by like reference signs where appropriate.
In the following description, some specific details are included to provide a thorough understanding of various disclosed embodiments. One skilled in the relevant art, however, will recognise that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In some instances, well-known structures associated with gripper assemblies and/or robotics, such as processors, sensors, storage devices, network interfaces, workpieces, tensile members, fasteners, electrical connectors, mixers, and the like are not shown or described in detail to avoid unnecessarily obscuring descriptions of the disclosed embodiments.
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. Thus, for example, reference to a robot including “a gripper assembly” includes a gripper assembly, or two or more gripper assemblies. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
With reference to
The system 100 further comprises a control system 108 including at least one controller 110 communicatively coupled to the manipulator apparatus 102 and the other components of the system 100 via the communication interface 104. The controller 110 comprises a control unit or computational device having one or more electronic processors, within which is embedded a set of control instructions provided as processor-executable data that, when executed, cause the controller 110 to issue actuation commands or control signals to the manipulator system 102, causing the manipulator 121 to carry out various methods and actions, e.g., identify and manipulate items. The one or more electronic processors may include at least one logic processing unit, such as one or more microprocessors, central processing units (CPUs), digital signal processors (DSPs), graphics processing units (GPUs), application-specific integrated circuits (ASICs), programmable gate arrays (PGAs), programmed logic units (PLUS), or the like. In some implementations, the controller 110 is a smaller processor-based device like a mobile phone, single board computer, embedded computer, or the like, which may be termed or referred to interchangeably as a computer, server, or an analyser. The set of control instructions may also be provided as processor-executable data associated with the operation of the system 100 and manipulator apparatus 102 included in a non-transitory processor-readable storage device 112, which forms part of the system 100 and is accessible to the controller 110 via the communication interface 104. In some implementations, storage device 112 includes two or more distinct devices. The storage device 112 can, for example, include one or more volatile storage devices, for instance random access memory (RAM), and one or more non-volatile storage devices, for instance read only memory (ROM), flash memory, magnetic hard disk (HDD), optical disk, solid state disk (SSD), or the like. A person of skill in the art will appreciate storage may be implemented in a variety of ways such as a read only memory (ROM), random access memory (RAM), hard disk drive (HDD), network drive, flash memory, digital versatile disk (DVD), any other forms of computer-and processor-readable memory or storage medium, and/or a combination thereof. Storage can be read only or read-write as needed.
The system 100 includes a sensor subsystem 114 comprising one or more sensors that detect, sense, or measure conditions or states of manipulator apparatus 102 and/or conditions in the environment or workspace in which the manipulator 121 operates, and produce or provide corresponding sensor data or information. Sensor information includes environmental sensor information, representative of environmental conditions within the workspace of the manipulator 121, as well as information representative of condition or state of the manipulator apparatus 102, including the various subsystems and components thereof, and characteristics of the item to be manipulated. The acquired data may be transmitted via the communication interface 104 to the controller 110 for directing the manipulator 121 accordingly. Such information can, for example, include diagnostic sensor information that is useful in diagnosing a condition or state of the manipulator apparatus 102 or the environment in which manipulator 121 operates. For example, such sensors may include contact sensors, force sensors, strain gages, vibration sensors, position sensors, attitude sensors, accelerometers, and the like. Such sensors may include one or more of cameras or imagers 116 (e.g., responsive in visible and/or nonvisible ranges of the electromagnetic spectrum including for instance infrared and ultraviolet), radars, sonars, touch sensors, pressure sensors, load cells, microphones 118, meteorological sensors, chemical sensors, or the like. In some implementations, the diagnostic sensors include sensors to monitor a condition and/or health of an on-board power source within the manipulator apparatus 102 (e.g., battery array, ultra-capacitor array, fuel cell array). In some implementations, the one or more sensors comprise receivers to receive position and/or orientation information concerning the manipulator 121. For example, a global position system (GPS) receiver to receive GPS data, two more time signals for the controller 110 to create a position measurement based on data in the signals, such as, time of flight, signal strength, or other data to effect a position measurement. Also, for example, one or more accelerometers, which also form part of the manipulator apparatus 102, could be provided on the manipulator 121 to acquire inertial or directional data, in one, two, or three axes, regarding the movement thereof.
The manipulator 121 may be piloted by a human operator at the operator interface 106. In human operator controlled or piloted mode, the human operator observes representations of sensor data, for example, video, audio, or haptic data received from one or more sensors of the sensor subsystem 114. The human operator then acts, conditioned by a perception of the representation of the data, and creates information or executable control instructions to direct the manipulator 121 accordingly. In piloted mode, the manipulator apparatus 102 may execute control instructions in real-time (e.g., without added delay) as received from the operator interface 106 without taking into account other control instructions based on sensed information.
In some implementations, the manipulator apparatus 102 operates autonomously. That is, without a human operator creating control instructions at the operator interface 106 for directing the manipulator 121. The manipulator apparatus 102 may operate in an autonomous control mode by executing autonomous control instructions. For example, the controller 110 can use sensor data from one or more sensors of the sensor subsystem 114, the sensor data being associated with operator generated control instructions from one or more times the manipulator apparatus 102 was in piloted mode to generate autonomous control instructions for subsequent use. For example, by using deep learning techniques to extract features from the sensor data such that in autonomous mode the manipulator apparatus 102 autonomously recognize features or conditions in its environment and the item to be manipulated, and in response perform a defined act, set of acts, a task, or a pipeline or sequence of tasks. In some implementations, the controller 110 autonomously recognises features and/or conditions in the environment surrounding the manipulator 121, as represented by a sensor data from the sensor subsystem 114 and one or more virtual items composited into the environment, and in response to being presented with the representation, issue control signals to the manipulator apparatus 102 to perform one or more actions or tasks.
In some instances, the manipulator apparatus 102 may be controlled autonomously at one time, while being piloted, operated, or controlled by a human operator at another time. That is, operate under an autonomous control mode and change to operate under a piloted mode (i.e., non-autonomous). In another mode of operation, the manipulator apparatus 102 can replay or execute control instructions previously carried out in a human operator controlled (or piloted) mode. That is, the manipulator apparatus 102 can operate without sensor data based on replayed pilot data.
The manipulator apparatus 102 further includes a communication interface subsystem 124, e.g., a network interface device, that is communicatively coupled to a bus 126 and provides bi-directional communication with other components of the system 100 (e.g., the controller 110) via the communication interface 104. The communication interface subsystem 124 may be any circuitry affecting bidirectional communication of processor-readable data, and processor-executable instructions, for instance radios (e.g., radio or microwave frequency transmitters, receivers, transceivers), communications ports and/or associated controllers. Suitable communication protocols include FTP, HTTP, Web Services, SOAP with XML, WI-FI™ compliant, BLUETOOTH™ compliant, cellular (e.g., GSM, CDMA), and the like.
The manipulator 121 is an electro-mechanical machine comprising one or more appendages, such as a robotic arm 120, and a gripper assembly or end-effector 122 mounted on an end of the robotic arm 120. The gripper assembly 122 is a device of complex design configured to interact with the environment in order to perform a number of tasks, including, for example, gripping, grasping, releasably engaging or otherwise interacting with an item. The manipulator apparatus 102 further includes a motion subsystem 130, communicatively coupled to the robotic arm 120 and gripper assembly 122, comprising one or more motors, solenoids, other actuators, linkages, drive-belts, and the like operable to cause the robotic arm 120 and/or gripper assembly 122 to move within a range of motions in accordance with the actuation commands or control signals issued by the controller 110. The motion subsystem 130 is communicatively coupled to the controller 110 via the bus 126.
The manipulator apparatus 102 also includes an output subsystem 128 comprising one or more output devices, such as speakers, lights, and displays that enable the manipulator apparatus 102 to send signals into the workspace in order to communicate with, for example, an operator and/or another manipulator apparatus 102.
A person of ordinary skill in the art will appreciate the components in manipulator apparatus 102 may be varied, combined, split, omitted, or the like. In some examples one or more of the communication interface subsystem 124, the output subsystem 128, and/or the motion subsystem 130 may be combined. In other examples, one or more of the subsystems (e.g., the motion subsystem 130) are split into further subsystems.
As previously mentioned, the manipulator 121 is configured to move articles, work pieces, or items from a first location, such as a storage tote box, and place the item in a second location, such as a delivery tote box, and
Firstly, it enables the gripper assembly 122 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 differ 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 often unknown when using position control schemes, and so the use of force sensors is required in order to measure gripping force. 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 132, 146 is not required. Instead, the output torque of the actuator 154 is controlled to match the desired force applied by finger assemblies 132, 146 to the item being manipulated. This is made possible by the novel arrangement of using a ball screw actuator assembly 134 that includes a direct connection between the actuator 154 and the ball screw shaft 138 to move the finger assemblies 132, 146. The ball screw actuator assembly 134 is a low friction transmission device, which, in this instance, is used to convert output torque of the actuator 154 to axially reciprocating movement of the finger assemblies 132, 146. Because it is a low friction transmission device, and in the absence of other transmission mechanisms, such as a gearing arrangement between the actuator 154 and the ball screw shaft 138, the applied or gripping force of the finger assemblies 132, 146 is directly proportional to the torque output of the actuator 154, meaning that the applied force can be accurately mapped with respect to the torque output to provide precise direct force control capability without the need for external force measurement.
Secondly, because the ball screw actuator assembly 134 provides a low friction transmission between the actuator 154 and finger assemblies 132, 146, the gripper assembly 122 is mechanically backdrivable. That is, the first and second finger assemblies 132, 146 can be moved manually, towards or away from each other, to effect rotation of the ball screw shaft 138. This ensures that the gripper assembly 122 has a degree of compliance, permitting safe physical interaction with its workspace.
In this example, the gripper assembly 122 further comprises two guide rails 156 supported within the housing 142 on either side of the ball screw shaft 138 by mounts 158. The guide rails 156 function, in part, to guide the lateral movements of the finger assemblies 132, 146 and to prevent the first and second ball screw nuts 136, 150 from rotating when the ball screw shaft 138 is rotated, fixing the rotational position of the first and second ball screw nuts 136, 150. To that end, the gripper assembly 122 further comprises first and second carriage assemblies 160, 162, each comprising two linear guides 164 slidably mounted on the guide rails 156. With reference to
In another example, shown in
In yet another example, shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2114638.6 | Oct 2021 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/078399 | 10/12/2022 | WO |
