GB2592405A

GB2592405A - Robotic device with tri-star wheels and actuated arm

Info

Publication number: GB2592405A
Application number: GB2002772.8A
Authority: GB
Inventors: Farnioli Edoardo
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2020-02-27
Filing date: 2020-02-27
Publication date: 2021-09-01
Anticipated expiration: 2040-02-27
Also published as: GB2592405B; GB202002772D0; CN115151175A; WO2021170979A1

Abstract

A robotic device 100 comprises an actuated robotic arm 105 having an end effector 112 and one or more powered joints 114, the position of the end effector relative to the robotic device being controllable to perform at least one task and a propulsion system 110 that includes a drive system and a set of tri-star wheels 120 coupled to the drive system 130. The robot may include a cleaning system, wherein the actuated robotic arm is coupled to the cleaning system and the task comprises at least one cleaning task such as wiping or vacuuming. Also disclosed is method of navigating a set of discontinuous surfaces with a robotic device that comprises driving a set of tri-star wheels of the robotic device to propel the robotic device in a direction of travel along a surface and during movement across a discontinuity along the surface, applying a force with an actuated robotic arm mechanically coupled to the robotic device to a portion of the surface to assist the movement. The discontinuity is preferably a stair or a step.

Description

ROBOTIC DEVICE WITH TM-STAR WHEELS AND ACTUATED ARM

Technical Field

The present invention relates to robotic devices. The present invention may be used to implement an autonomous domestic robot.

Background

Human environments present unique challenges for robotic devices. These environments are designed for navigation and manipulation by human beings; however, human beings are extremely complex biological entities that are difficult to replicate with humanoid robots. For example, it has long been a desire to provide domestic robotic devices that can help with tasks within a home. However, homes have discontinuous surfaces like stairs and steps that cause many robotic devices problems during navigation. This is often the case for even single floor apartments, as small level changes between rooms are common. Many domestic robotic devices are low-profile devices that are adapted to navigate continuous planar surfaces.

CN108553030A describes an intelligent stairway cleaning and collecting robot. The intelligent stairway cleaning and collecting robot comprises a robot body, wherein a separating plate is arranged in the robot body and is used for separating an inner cavity of the robot body into a garbage collecting cavity and an element installation cavity. A dustbin container is arranged in the garbage collecting cavity and the top part of the robot body is provided with an opening.

CN106426083A describes a robot cleaner stair climbing device. Track-laying climbing mechanisms are installed on two sides of a main frame and an attached frame. A bottom plate is installed under the middle of the main frame, and a baffle is installed on the rear end of the bottom plate in a hinged mode. When the robot is going upstairs or downstairs, the robot and the stair climbing device meet and the baffle is lowered to the ground. The robot climbs up the bottom plate through the baffle, and then the baffle turns up and stands upright to block the robot. After going up or down, the baffle is lowered to the ground, and the robot crawls through the baffle to the floor. CN105996910A describes a domestic stair automatic cleaning robot, which comprises a dust-collection cleaner which is provided with a walking mechanism. A horizontal motion driving mechanism is provided by which the dust-collection cleaner and mounting racks are driven to perform relative motion in the longitudinal and horizontal directions. Telescopic brackets are also provided which are connected to the connecting racks and are capable of expanding and folding in a vertical direction, together with telescopic driving devices for driving the telescopic brackets to expand/fold in the vertical direction.

US2013125338A1 describes a vacuum cleaner with a unique shape which allows it to be placed in a stable position on a flight of stairs yet also remain suitable for use on a flat surface such as a floor.

KR I 01016775B I describes a stair robot cleaner that is provided to enable a user to conveniently clean a set of stairs Despite these approaches it is desired to develop robotic devices that may easily navigate human environments and perform a variety of tasks. It is further desired to develop robotic devices that may be provided with an autonomous navigation system that can successfully interact with, and/or navigate, a human environment with minimal human assistance It is desired that these robotic devices are robust and not prone to failure.

Summary

According to a first aspect of the present Invention there is provided a robotic device comprising an actuated robotic arm comprising an end effector and one or more powered joints, the position of the end effector relative to the robotic device being controllable to perform at least one task and a propulsion system. The propulsion system comprises a drive system and a set of tristar wheels coupled to the drive system.

The robotic device is thus able to perform at least one task by actively positioning the actuated robotic arm in space while also being able to navigate discontinuous terrain and obstacles using the set of tri-star wheels. The set of tri-star wheels further provide stability while moving the actuated robotic arm by providing at least two points of contact with a ground surface during the task (e.g. via two of a set of three outer wheels of each tri-star wheel). The robotic device may thus easily navigate human environments and perform a variety of tasks. The robotic device may be able to navigate a variety of surfaces and perform the variety of tasks in a manner that is faster, more robust and less prone to failure than the comparative implementations described above. As such the robotic device may form the basis of an autonomous robotic device.

In certain examples, the robotic device comprises a cleaning system, wherein the actuated robotic arm is coupled to the cleaning system and the task comprises at least one cleaning task.

For example, the robotic device may comprise an autonomous robot to perform domestic cleaning tasks. While the actuated robotic arm may be configured to move the end effector within space to perform the cleaning task, it may also be configured to use the actuated robotic arm for auxiliary functions such as for stabilising the robotic device during navigation. The set of tri-star wheels may enable the robotic device to navigate discontinuous surfaces within a home, such as stairs, steps or other level changes, and the robotic device may be configured to perform the cleaning task while navigating these discontinuous surfaces. In one case, the robotic device may be configured to perform the cleaning task while also applying a stabilising force, e.g. performing the cleaning task may involve applying a force to a surface or object that also stabilises the robotic device while the robotic device is using the set of tri-star wheels to climb stairs or steps.

The cleaning system may comprise a vacuum system, wherein an aperture at the end effector of the actuated robotic arm is maintainable at a low pressure using the vacuum system.

For example, a vacuuming head may be provided at the end effector. In this case, while climbing a set of stairs, e.g. within a home, the robotic device may vacuum the stairs. The act of vacuuming may also provide a stabilising force that aids the climbing action of the set of tri-star wheels. This may result in fewer incidents of toppling while increasing the speed and robustness of the stair climbing.

In certain examples, the actuated robotic arm comprises a plurality of joints. For example, the actuated robotic arm may have three to six degrees of freedom. For simple implementations that are easier to configure, the actuated robotic arm may have a lower number of degrees of freedom. In this case, additional positioning, such as rotation perpendicular to a supporting surface, may be performed by differential drive of the set of tri-star wheels. More advanced implementations, e.g. where increased dexterity is desired, may have a larger number of degrees of freedom and multiple degrees of freedom for one or more joints. For example, the robotic device may be configured with a gripper to perform manual tasks within a domestic environment.

In certain cases, the set of tri-star wheels support the robotic device upon a surface and the actuated robotic arm is configured to perform the at least one task above or below the surface. The set of tri-star wheels may allow a compact form factor for the robotic device that provides improved navigational ability within the home. However, within human environments there are often locations where a task is to be performed (e.g. vacuuming a chair) that are not accessible to a body of the robotic device. The actuated robotic arm thus allows off-surface tasks to be performed in a manner that is not possible with comparative form factors, such as those described

in the background.

In certain cases, the robotic device comprises a chassis housing at least the propulsion system, wherein the actuated robotic arm is mechanically coupled to the chassis, and wherein the set of tri-star wheels comprise a pair of tri-star wheels arranged on either side of the chassis. This provides a particularly compact form factor where the tri-star wheels can provide stability via two contact points yet be coupled to the propulsion system via a single drive shaft for each tri-star wheel. The robotic device may thus be of a size that is suited to navigation and storage within a domestic (e.g. home) environment. This form factor also better enables the robotic device to avoid getting in the way while human beings are present in the surrounding environment.

In certain examples, the end effector comprises an interface for removably mounting a plurality of tools. For example, the plurality of tools may comprise one or more of a gripper, a brush and a vacuuming head. In this case, the tri-star wheels may provide a stable base while the end effector moves to switch tools within the plurality of tools. This can then enable multi-task functions that increases the utility of the robotic device, e.g. especially with regard to domestic environments.

In certain examples, a controller is electronically coupled to the propulsion system and the actuated robotic arm, wherein the controller is configured to control at least the actuated robotic arm. The controller may be configured to control the actuated robotic arm to assist the propulsion system when navigating discontinuous surfaces. For example, the controller may be configured to use the actuated robotic arm to apply a stabilising force to a surface behind the robotic device during forward motion using the set of tri-star wheels or may be configured to apply impedance control to adjust the one or more powered joints based on a force applied to the end effector. By controlling the actuated robotic arm and the propulsion system using a common controller, the form of the robotic device within space may be controlled. For example, the controller may act to control a position of the actuated robotic arm when performing a task to provide for a particular centre of gravity that affects propulsion with the propulsion system. The controller may thus provide integrated control of the robotic device. In certain cases, neural network architectures may be provided as part of the controller so as to set the position of the end effector dependent on control of the propulsion system (and/or vice versa).

According to a second aspect of the present invention there is provided a method of navigating a set of discontinuous surfaces with a robotic device, the method comprising driving a set of tri-star wheels of the robotic device to propel the robotic device in a direction of travel along a surface and during movement across a discontinuity along the surface, applying a force with an actuated robotic arm mechanically coupled to the robotic device to a portion of the surface to assist the movement.

The method thus improves how a robotic device comprising a set of tri-star wheels and an actuated robotic arm navigates an environment. This may allow improved navigation of complex domestic human environments. The actuated robotic arm allows a force to be actively applied, e.g. via power supplied to one of more actuators of the actuated robotic arm, and as such controlled to improve navigational handling. The actuated robotic arm may be primarily designed to perform a task or function that is not assisting the movement, such as performing a cleaning task. In these cases, the actuated robotic arm may be actively re-purposed, in use, to provide stability of movement.

The robotic device may comprise an autonomous vacuuming device and the discontinuity comprises a stair or a step. The method may thus allow vacuum cleaning of many different areas within a domestic environment.

In certain cases, applying a force with the actuated robotic arm comprises, during contact between a wheel portion of at least one of the set of tri-star wheels and a discontinuous first surface, applying a force to a second surface situated behind the robotic device in the direction of travel with the actuated robotic arm. For example, a tool coupled to the end effector may contact the surface to perform a task such as a cleaning task upon the surface but also simultaneously provide a force that stabilises the robotic device during navigation of the discontinuous surface. This may enable the robotic device to robustly climb up a set of stairs. In other cases, a force may be applied to a second surface situated in front of the robotic device, e.g. when climbing down a set of stairs. In certain cases, the method comprises performing a cleaning function before, during or after applying the force. For example, the application of the force may form part of a general procedure of operation for the robotic device where a primary function is to provide the cleaning function. This enables the force to be applied as an auxiliary function performed by the robotic arm. In certain cases, the cleaning function may be programmed and/or configured to apply the force without needing to significantly redesign the cleaning function.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figures IA to IC are schematic diagrams respectively showing a side view, a front view and a rear view of a first example robotic device; Figure ID is a schematic diagram showing the first example robotic device performing a task; Figures 2A to 2D are schematic diagrams showing a second example robotic device performing a stair climbing procedure; Figures 3A and 3B are schematic diagrams respectively showing a side view and a front view of a third example robotic device; Figure 4 is a schematic diagram showing an example planetary gear arrangement for implementing a propulsion unit for a robotic device; Figure 5 is a schematic diagram showing degrees of freedom for an example actuated robotic arm; Figure 6 is a schematic diagram showing an example tool exchange procedure; Figure 7 is a system diagram showing certain example control components for a robotic device; Figures 8A and 8B are schematic diagrams respectively showing a cut-away of a side and a front cross-section of a fourth example robotic device; Figure 9A is a schematic diagram showing an example joint for an actuated robotic device; Figure 9B is a schematic diagram showing a side view of a fifth example robotic device; Figures 9C and 9D are schematic diagrams respectively showing a side view and a front view of a sixth example robotic device; and Figure 10 is a flow diagram showing a method of navigating a set of discontinuous surfaces with a robotic device according to an example.

Detailed Description

Certain examples described herein provide a form factor for a robotic device that may be used to navigate human environments. The form factor consists of a set of tri-star wheels and an actuated robotic arm. This form factor may be particularly useful for autonomous cleaning devices.

For example, it may enable robotic cleaning devices to navigate stairs and steps, and allow for "off-floor" tasks. These "off-floor" tasks may include the cleaning of furniture or areas that are not accessible to the body of the robotic device. As used herein, the term "task-refers to an undertaking to be performed by the robotic device, such as a discrete job that involves positioning the end effector within space to achieve a desired goal This goal may be the cleaning and/or manipulation of objects within an environment.

Certain examples described herein use one or more "tri-star wheels". A tri-star wheel is a form of location unit that comprises three rotating wheels that are equally spaced around a central rotating shaft. The outer three wheels may be seen to form a satellite or planetary arrangement around the central rotating shaft. The outer three wheels may be mounted towards the end of a three-spoke hub, where each spoke comprises an elongate member that is spaced from the other members by approximately 120 degrees. A planetary gearing arrangement (e.g. a form of gear chain) may be used to power each outer wheel from a common drive shaft.

Examples described herein use an actuated robotic arm. In these examples, the term "actuated" is used to indicate that one or more joints of the robotic arm may be moved by way of one or more actuators, such as joint motors or electro-active polymers. Hence, the actuated robotic arm is configured to move within its environment. Although the term "arm" is used, the robotic arm may be any form of jointed limb or mechanical assembly that is capable of moving an end effector within space.

In certain cases, the combination of one or more tri-star wheels and an actuated robotic arm provides synergistic effects. For example, the tri-star wheels may provide additional stability for the movement of the actuated robotic arm and the actuated robotic arm may apply additional forces to facilitate navigation over obstacles using the tri-start wheels.

Figures 1A to 1D show a first example robotic device 100. Figure lA shows a side view of the first example robotic device 100. The first example robotic device 100 comprises an actuated robotic arm 105 and a propulsion system 110. The actuated robotic arm 105 comprises an end effector 112 and one or more powered joints 114. The one or more powered joints 114 act to control a position of the end effector 112 within three-dimensional space. The position of the end effector 112 relative to the robotic device 105 is controllable to perform at least one task.

The propulsion system 110 comprises a set of tri-star wheels 120 and a drive system 130. In the example of Figures lA to 1D, the set of tri-star wheels 120 comprises two tri-star wheels that are arranged on either side of a body 140 of the robotic device 100. Each tri-star wheel 120 is coupled to the drive system 130 and the drive system 130 provides a torque to propel the set of tri-star wheels 120 and move the robotic device 100 along a surface. The drive system 130 may comprise one or more motors and/or suitable gearing to effect movement of each tri-star wheel, e.g. including movement of one or more of the wheel assembly or hub and a set of outer rotating wheels.

In the first example robotic device 100, the actuated robotic arm 105 comprises three] oints: an elbow joint 114, a wrist joint 150 and a shoulder joint 160. The shoulder joint 160 is visible in Figures 1B and 1C. The joints of the actuated robotic arm 105 are coupled by mechanical linkages or "links". Figure 1A shows a forearm link 116 that mechanically couples the elbow-joint 114 to the wrist joint 150 and an upper arm link 118 that mechanically couples the elbow joint 114 to the shoulder joint 160. Each link may comprise a rigid elongate member. Each link may be a single unit or multiple coupled sub-units. Each link may have solid and/or hollow portions. In one case, a link may comprise a hollow tube and/or a frame of rigid material such as steel, aluminium or carbon fibre. The three joint example of Figures IA to 1D may be relatively cheap and straightforward to implement and control, yet provide a suitable range of movement for performing reasonably complex tasks with a desired amount of dexterity.

In the first example robotic device 100, a tool 152 is mechanically coupled to the end effector 112. The tool 152 may be moveable by way of the wrist joint 150. The tool 152 may be adapted to carry out a task within a human environment. In one case, the task may be a dry or wet cleaning operation or task, such as wiping and/or vacuuming In one case, the tool may be exchangeable, e.g. as described in later examples.

In the first example robotic device 100, the drive system 130 of the propulsion system 110 drives each of the two tri-star wheels. The drive system 130 may comprise a single part or multiple parts. For example, as seen in Figures 1B and 1C, the drive system comprises two lateral parts that couple the body 140 of the robotic device 100 to each tri-star wheel 120. These lateral parts may comprise separate drive motors, e.g. one for each tri-star wheel 120, or a common drive motor that provides a torque to each tri-star wheel 120 via one or more drive shafts. In certain cases, the propulsion system 110 may comprise an electric drive system, wherein one or more drive motors of the drive system 130 are powered by one or more electric batteries that are contained within the body 140 of the robotic device 100. The one or more electric batteries may be rechargeable, e.g. by electrically coupling the robotic device 100 to a power supply. In another case, the propulsion system 110 may comprise an electric drive system, wherein one or more drive motors of the drive system 130 are powered by one or more wired and/or wireless electricity sources (e.g. a cable plugged into a mains supply and/or an inductive power supply).

In Figures IA to ID, each tri-star wheel 120 comprise a tri-spoke hub 124. The tri-star hub 124 may comprise a single unit or multiple coupled parts. It forms a frame for the tri-star wheel. The tri-spoke hub 124 comprises three spokes or arms that extend out from a central portion. Each spoke is equally spaced around the hub, e.g. at an angle of approximately 120 degrees. At the end of each spoke is an outer rotating wheel 122. Hence, there are three outer rotating wheels 122 in each tri-star wheel. Both the tri-spoke hub 124 and the outer wheels 122 may rotate about respective axes. In one case, the tri-spoke hub 124 may comprise an assembly that additionally contains a gear arrangement to couple the drive system 130 to each outer rotating wheel 122. In normal operation, e.g. as shown in Figure 1A, the outer rotating wheels 122 that are in contact with the ground (e.g. wheels 122-B and 122-C in Figure 1A) may rotate via a torque applied by the drive system. As will be described in more detail in relation to Figures 2A to 2D, responsive to an applied force that prevents rotation of one of the outer rotating wheels 122, e.g. the wheel meeting a discontinuity in a surface the robotic device 100 is navigating over, the tri-star wheel 120 may rotate about the centre of the tri-spoke hub 124, e.g. relative to the body 140. In this case, the tri-star wheel 120 may pivot about an axis of the constrained one of the outer rotating wheels. Further details on tri-star wheel arrangements may be found in US Patent 3,348,518 and the paper by Bozzini et al titled "Design of the small mobile robot Eqi.q-2", both of which are incorporated by reference herein.

It should be noted that the first example robotic device 100 is but one of many potential configurations of a robotic device having a set of tri-star wheels and an actuated robotic arm. At least different] oint arrangements, different wheel and joint sizes, different body arrangements and different numbers of wheels are envisaged, and certain examples of different arrangements are shown in the later Figures.

Figure 1D shows an example of how the first example robotic device 100 may be used to perform a task within an environment. In one case, the first example robotic device 100 may comprise a cleaning system wherein the actuated robotic arm 105 is coupled to the cleaning system and arranged to perform at least one cleaning function. For example, the cleaning system may comprise a vacuum system, wherein an aperture at the end effector 112 of the actuated robotic arm 105 is maintainable at a low pressure using the vacuum system. h] this case, the tool 152 may comprise a vacuuming head and the robotic device 105 may comprise an autonomous vacuum cleaner. The vacuum system may comprise a cyclonic vacuum system and/or the robotic device may comprise an autonomous cyclonic vacuum cleaner.

Figure ID shows an item of furniture 180. The item of furniture 180 may be a chair, shelving unit, worktop, desk etc. The item of furniture 180 rests on a floor surface 170. The first example robotic device 100 also rests on the same surface 170 via two outer rotating wheels 122B, 122-C within each tri-star wheel 120. The tri-star wheel arrangement provides stability for the performance of a task above the surface 170. For example, in Figure 1D, the actuated robotic arm 105 is used to perform a task on the item of furniture 180. This may be described as an "off-surface" or "off-floor" task as the tool 152 is located above the surface 170. Although the example of Figure ID shows an example of a task being performed above the surface 170, the task may also be performed below the surface, e.g. as shown in Figures 2A to 2D. In the case where the tool 152 comprises a vacuuming head, the actuated robotic arm 110 may be manipulated to allow the tool 152 to cover an area of the item of furniture 180, which may involve vacuuming a chair or sofa. The primary purpose of the actuated robotic arm may thus not comprise providing a stability function for the robotic device. However, in certain described examples, the actuated robotic arm may provide such a stability function as an auxiliary purpose, e.g. in addition to one or more defined tasks.

In a co-ordinate system where the surface 170 defines an x-y plane, the position of the end effector 112 at least within a perpendicular z-axis (e.g. vertically in Figure 1D) may be determined by controlling the rotation of one or more of j oints 114, 150 and 160. In one case, the position of the wrist joint 150 within the z-axis is controlled by changing the angle of one or more of the elbow joint 114 and the shoulder joint 160, wherein the wrist joint 150 alters the orientation of a plane of the tool 152 within the environment. In this case, there may be three degrees of freedom. In other cases, one or more of the joints may also be able to rotate around an axis that is parallel to the z-axis, and as such the position of the end effector 112 within the x-y plane may also be controlled. In this latter case, the shoulder joint 160 may comprise either a ball joint or a two-joint assembly that allows respective rotation around axes parallel to both the z and y axes. This, for example, may allow the positioning of the end effector 112 with six degrees of freedom. In cases, where the movement of the end effector 112 is limited to a plane of movement (e.g. the plane of Figure ID), then the robotic device 100 may rotate upon the surface 170 to move the end effector 112 within the x-y plane. For example, the drive system 130 may provide a differential torque to each of the tri-star wheels 120 to allow rotation of the robotic device about a centre of the body 140. The one or more joints of the actuated robotic arm may be rotated using one or more electronic motors. In one case, a control system of the robotic device 100 may determine one or more of a joint angle and a torque to apply to move the actuated robotic arm 105 within the environment.

Figures 2A to 2D show a second example robotic device 200 performing a stair climbing procedure. The second example robotic device 200 is shown as a variation of the first example robotic device 100, but may equally comprise one of the other example robotic devices described herein. Unless specified otherwise, described features of the other examples, including the first example robotic device 100, apply to the second example robotic device 200. As described with reference to Figures 1 A to 1D, the robotic device 200 has a set of tri-star wheels and an actuated robotic arm. The robotic device 200 is shown navigating a discontinuous surface; in this example, a set of stairs 205. The set of stairs 205 feature step changes in height. For example, the stairs 205 consist of substantially vertical planar portions 272 and substantially horizontal planar portions 274. Other forms of discontinuity may also be navigated in a similar manner including obstacles on a surface, uneven terrain, steps (e.g. one or more changes in surface orientation), kerbs, and differences in surface height in different rooms (e.g. due to room geometry and/or floor construction). Generally, the form factor of the robotic device 200 enables a large number of different environments with non-planar floor surfaces to be navigated.

In Figure 2A, the robotic device 200 is resting upon a horizontal surface 274 of the stairs 205. Two of the outer rotating wheels of each tri-star wheel provide stability and contact the horizontal surface 274. While in this position, the end effector 210 may be moved to perform a task upon one or more of the surfaces 272, 274 of the stairs 205. For example, the end effector 210 may perform a cleaning function such as vacuuming or wiping the stairs. While performing the task, a drive system of a propulsion system may be deactivated, e.g. such that the tri-spoke hub or outer wheels of the tri-star wheels do not rotate.

Responsive to the robotic device 200 being ready to continue moving up the stairs 205, e.g. once the task has been completed in relation to one or more of the sub-surfaces 272 and 274, the drive system may be engaged. The robotic device 200 may move forward until the substantially vertical surface 272 prevents further movement of the leading outer wheel in each tri-star wheel.

At this point, the tri-star wheels may begin to rotate about the centre of each tri-spoke hub. For example, this may occur responsive to the local friction between the leading outer wheel and an obstacle such as surface 272 exceeding a threshold, e.g. that is sufficient to block the forward motion of the outer wheel. As shown in Figure 2B, rotation of the tri-star wheel about the centre of each tri-spoke hub and a pivoting about the leading outer wheel moves the body of the robotic device 200 up and over the discontinuity in the surface.

As also shown in Figure 2B, during the stair climbing action of the tri-star wheel, the end effector 210 may apply a force to one of the surfaces 272 or 274 to help propel the robotic device 200 upwards. The force applied by the end effector 210 may also (or alternatively) stabilise the robotic device 200 during the stair climbing procedure such that it does not fall backwards or tip over to the side. For example, the force applied by the end effector 210 may aid the rotation of the set of tri-star wheels about the centre of each tri-spoke hub and (at least partially) compensate for the weight of the body of the robotic device 200. In one case, the end effector 210 may perform a task and provide a propulsion and/or stability function, e.g. a vacuuming operation may be performed on the horizontal surface 274 of the stair while the tri-star wheels of the robotic device are navigating the discontinuity in the surface.

Figure 2C shows how once contact is made between a new leading outer wheel and a horizontal surface, the new leading outer wheel may begin to propel the robotic device further forward (via friction between this wheel and the surface). The previously leading outer wheel may also rotate and propel the robotic device 200 upwards via friction between this wheel and the vertical surface 272. The end effector 210 may additionally be applied as before. Figure 2D shows how once the previously leading outer wheel travels over the lip of the stair, the two outer wheels that contact the ground may be used again to propel the robotic device forward. The end effector 210 may finish a task upon the stairs and then be raised upwards to start performing a task on the upper-most surface where the robotic device 200 now resides.

The tri-star wheel arrangement may be configured to provide a stair climbing functionality as known in the art. In certain cases, a cylindrical body may be used that may allow rotation of the robotic device 200 without rotation about the centre of the tri-spoke hub of the tri-star wheels, e.g. the robotic device 200 may rotate to new positions while navigating discontinuities in a surface. In the described example of Figures 2A to 2D, rotation about the centre of the tri-spoke hub of the tri-star wheels allows an orientation of the body of the robotic device to be maintained during the stair climbing procedure. Although in Figure 2A the horizontal surface 274 accommodates two outer rotating wheels, in other stair configurations the horizontal surface 274 may be narrower in the dimension of the Figure and as such only one outer wheel may be accommodated. In this case, a similar procedure may still be performed, e.g. with a movement similar to that shown in Figures 2B and 2C. Indeed, in these cases, the additional force provided by the end effector 210 may provide additional stability and upward propulsion.

Figures 3A and 3B show a third example robotic device 300. The third example robotic device 300 may be seen as a variation of the first example robotic device 100 shown in Figures IA to 1D. The third example robotic device 300 comprises an actuated robotic arm 305 and a propulsion system 310 similar to the example of Figures IA to ID. However, in this example the outer rotating wheels 322 are a different size; namely, they are larger and extend towards each other. The configuration shown in Figures 3A and 3B may be more suited to rough terrain and/or be more robust to tumbling motion. In one case, the outer wheels of the tri-star wheels may be interchangeable. In this case, the robotic device 300 may comprise the robotic device 100 but with an alternative set of coupled outer rotating wheels 322.

In one case, the radius of the outer rotating wheels rw and/or the length /, of each spoke within the tri-spoke hub may be selected to provide for different climbing abilities. Further information is provided in the aforementioned publication by Bozzini et at In general, if the ratio / Fir is increased, the robotic device is able to climb over higher obstacles based on a motion that using the spokes as a form of limb for a stepping motion. If the ratio /s/ rw is decreased, the robotic device is more suited to locomotion using two of the outer wheels and the gearing arrangement may be more protected. A lower limit for the ratio may be: 1 / cos(30°), e.g. a case where the outer rotating wheels are in an interference limit condition. The described example tri-star wheels, e.g. with a tri-spoke hub and a set of three equally-spaced outer wheels, allows efficient stair climbing with a design that may be implemented with a low number of moving parts, increasing robustness and reducing failure. The tri-spoke design further enables one or more of the spoke size and the outer wheel size to be configured to suit an environment of use, allowing different designs to be easily configured for different environments.

Figure 4 shows an example of a gearing arrangement 400 that may be used for the tri-star wheels. The gearing arrangement 400 of Figure 4 is a so-called planetary gearing arrangement comprising a central solar gear 410 and a plurality of outer planetary gears 420, 430. The central solar gear 410 may be driven by a drive system as described herein. The tri-spoke hub assembly may be configured to rotate independently of a drive axle for the central solar gear 410. The trispoke hub thus acts as a planet carrier. Each spoke of the tri-star arrangement has, in this example, two planetary gears: a first inner planetary gear 420 and a second outer planetary gear 430. The outer rotating wheel for each spoke may be driven by the second outer planetary gear 430. Although two planetary gears are shown, other gear chain configurations with greater or fewer gears may alternatively be used. The size of the central solar gear 410 and the planetary gears 420, 430 may be determined based on design considerations. This arrangement provides simple drive control of the tri-star wheels, e.g. propulsion may be provided by a single drive axle to the three outer rotating wheels. This then provides a simplicity of form factor that allows a compact size for domestic applications and robustness for repeated use.

In certain examples described herein, including the example of Figure 4, each tri-star wheel has two degrees of freedom including one degree of freedom for the rotation of the outer rotating wheels and one degree of freedom for the rotation of the tri-spoke hub. In the arrangement of Figure 4, different motions may be obtained using one transmission system (e.g. driven by the drive system) by selectively locking and/or unlocking these degrees of freedom. In the stair climbing procedure shown in Figures 2A to 213, the robotic device is able to passively modify its locomotion from an advancing mode that uses two of the outer rotating wheels to a climbing mode where it climbs over discontinuities. In the advancing mode, the tri-spoke hub is mechanically free to rotate around its axis, but the weight of the robotic device and the contact forces between the outer rotating wheels and a ground plane constrain the angular position of the robotic device. In the climbing mode, local friction between a leading outer wheel and an obstacle blocks the rotation of this wheel and leads to rotation of the tri-spoke hub. The robotic device thus rotates about the leading outer wheel to climb over the obstacle.

Figure 5 shows three degrees of freedom for an example actuated robotic arm 500. A first degree of freedom -91- is provided by shoulder joint 560. The shoulder joint 560 may extend around a circumference of a body of the robotic device or may be localised at a top of the body.

The former case may allow omni-directional operation of the robotic device, whereas the latter case uses a preferred orientation of the body of the robotic device. The shoulder joint 560 may allow rotation within a limited range of angles, e.g. 120° or 180°, or full 360° rotation. A second degree of freedom -02 -is provided by elbow joint 514. A third degree of freedom -03 -is provided by wrist joint 550. As described previously, the third degree of freedom may allow for rotation of the plane of the end effector and/or an attached tool 552. Similar to the shoulder joint 560, each of the elbow joint 514 and the wrist joint 550 may have a defined range of rotation. The elbow joint 514 may provide a greatest range of possible rotations of the three joints, such as a substantial portion of the circumference around the joint, within the constraints imposed by the presence of the linkage members. The wrist joint 550 may either provide for a relatively large range of movement or be restricted to a predefined range of movement.

In certain cases, one or more of the elbow-joint 514, the wrist joint 550 and the shoulder joint 560 may comprise a ball joint or two-joint assembly to allow further rotation in at least a plane perpendicular to the plane of the degrees of freedom shown in the Figure. For example, the wrist joint 550 and the shoulder joint 560 may be implemented as ball joints to increase a range of movement if required. However, a restricted range of movement, e.g. limited to three degrees of freedom, may be easier to control, e.g. in an autonomous implementation.

It should be noted that an actuated robotic arm may differ from that shown in Figure 5 yet still provide for multiple degrees of freedom for the end effector within an environment. For example, electro-active polymers may be arranged around a pivoted joint and controlled by an electrical current. In certain cases, a camera arrangement may be disposed on the robotic device to enable visual feedback of the position of the end effector within three-dimensional space. In one case, one or more neural network architectures may be used to process signals from one or more of a set of joint actuators, position sensors and a video camera, and to generate signals to control the set of joint actuators.

Figure 6 shows how a tool attached to an end effector may be exchanged. Figure 6 shows a robotic device 600, which may be an implementation of the first example robotic device 100 of Figures IA to 1D, and a tool exchange unit 610. In Figure 6, the tool exchange unit 610 comprises a substantially vertical cabinet with sub-compartments 612, 614 that may be accessed via at least a front aperture. The arrangement of Figure 6 is provided for example, other orientations including horizontal may also be used, although a substantially vertical tool exchange unit 610 may allow for simpler control procedures for tool exchange. Within each sub-compartment 612, 614 are a number of exchangeable tools 616, 618. In Figure 6, two exchangeable tools 616, 618 are shown as an example, although in implementations a different plurality of exchangeable tools may be provided. In Figure 6, a first exchangeable tool 616 comprises a vacuuming head and the second exchangeable tool 618 comprises a gripper. The plurality of exchangeable tools may take many forms and may include different grippers, brushes, vacuuming head, mops, pans or bins, dusters, wet-cleaning appendages such as sprays, cushioned heads for applying a moving force etc. Each exchangeable tool may be mounted within a frame or support within the sub-compartments. In one case, the frame or support may aid correct alignment of the exchangeable tools within the sub-compartment. The exchangeable tools may be retained within the sub-compartments using a retaining force, which may be mechanical (e.g. spring-loaded catches) and/or magnetic.

To use the exchangeable tools within the tool exchange unit 610, the end effector of the robotic device 600 comprises a tool interface 652. The tool interface 652 may be mechanical and/or magnetic. The tool interface 652 is configured to removably mount one of the plurality of exchangeable tools, e.g. for performing a task. The tool interface 652 may be coupled to a wrist joint 650 to control orientation, e.g. as described above. In use, as shown in Figure 6, the robotic device 600 actuates one or more joints of the actuated robotic arm to move the tool interface 652 into a selected sub-compartment to mount a selected one of the first and second exchangeable tools 616, 618. For example, in Figure 6, the robotic device 600 may be attempting to mount the vacuuming head 616, or may have just deposited the vacuuming head 616 and be moving to attach the gripper 618. Movement is shown by arrow 620 in Figure 6. One or more of the sub-compartments 612, 614 and the interface 652 may comprise actuated locking components to lock and/or unlock an exchangeable tool in place. These locking components may be electrically controlled (e.g. by the robotic device and/or by the sub-compartment based on sensor data). The interface 652 may provide for both mechanical and electrical coupling with the robotic device 600. An electrical coupling may be provided by electrical contacts (e.g. in a plug and socket arrangement) and may provide one or more of power and control signals. For example, one or more actuators on the gripper 618 may be both powered and controlled by the robotic device 600 via the interface 652. An electrical coupling to the body of the robotic device may be provided by a wired connection that extends along the length of the actuated robotic arm and/or a wireless connection. Exchangeable tool sets may allow the robotic device to use the actuated robotic arm to perform a plurality of different tasks, e.g. vacuuming and moving objects and dusting, which further enhances the utility of the robotic device without significant change to a base form factor, enabling simpler control (e.g. a general control procedure may be re-used for different tasks) and expandability.

Figure 7 shows an example control system 700 for a robotic device. The example control system 700 comprises certain example control components for the robotic device. The example control system 700 may be used to implement a control function in any of the example robotic devices described herein. The example control system 700 of Figure 7 relates to an autonomous cleaning device; however, certain control components may also be shared by other examples.

The example control system 700 comprises internal body components 710 that may be supplied as part the body of the robotic device (e.g, may be mounted on or in the body). The internal body components 710 comprise a controller 720, a drive control system for a first tri-star wheel 730, a drive control system for a second tri-star wheel 735, a set of joint control systems 740 to 744, and a cleaning control system 750. In Figure 7, the set of joint control systems 740 to 744 comprise a first joint control system 740, which may control a shoulder joint mounted upon the body of the robotic device, and a set of nth joint control systems 742 to 744, which may control a plurality of joints that are external to the body of the robotic device, such as the previously described elbow and wrist joints. The set of j oint control systems 740 to 744 may be coupled in a number of ways as known in the art, including a serial daisy-chain style arrangement or a parallel coupling. This is indicated by the dashed arrows in Figure 7. The drive control systems 730, 735 are shown as two separate control systems, e.g. for two separate motors, but in certain cases these may be implemented by a single control system for the set of tri-start wheels. The drive control systems 730, 735 are configured to control the set of tri-star wheels, including controlling a velocity and/or acceleration of one or more wheels, and, in certain cases, any rotation locking mechanisms. The drive control systems 730, 735 may control a torque that is applied by one or more electric motors in response to signals received from the controller 720. The drive control systems 730, 735 may form part of a propulsion system for the robotic device. The cleaning control system 750 controls cleaning functions of the robotic device, for example activation of a vacuuming unit, vacuum motor control, control of any dry and/or wet cleaning components (e.g. including those mounted on the end effector), and cleaning sensor processing.

The controller 720 may comprise one or more processors, including one or more microprocessors, central processing units and/or graphical processing units, and a set of memory.

The controller 720 is communicatively coupled to the example control components to control an action of the robotic device. In Figure 7, this coupling is achieved via systems bus 760. The controller 720 in Figure 7 is configured to control at least the actuated robotic arm via the set of joint control systems 740 to 744. Different levels of control may be provided, e.g. in one case the controller 720 may provide a desired relative three-dimensional position that is converted by the set of joint control systems 740 to 744 into joint actuator commands or in another case the controller 720 may provide the joint actuator commands themselves, which are then effected by the set of joint control systems 740 to 744. The controller 720 may also control the drive control systems 730, 735 to propel the robotic device within an environment. As such, the controller 720 may be configured to control the actuated robotic arm to assist the propulsion system when navigating discontinuous surfaces, such as by applying a stabilising force to a surface behind the robotic device during forward motion using the set of tri-star wheels. In one case, the controller 720 is configured to apply impedance control to adjust the one or more powered joints based on a force applied to the end effector. Impedance control may reduce damage to objects and people when the robotic device is interacting within an environment.

In these cases, the stabilising force may be considered to be separate from a task to be performed by the actuated robotic arm, e.g. the task is not to (primarily) apply a stabilising force. However, control of the actuated robotic arm may be configured to provide the stabilising force as a by-product or auxiliary function of performing the task. The stabilising force may be applied before, during and/or after performing the task. For example, by vacuuming a stair with a vacuuming head attached to the end effector, a force is applied to the stair. This force may be a stabilising force and have a stabilising effect, however, the primary task of the robotic device is to vacuum the stair. Similarly, following or before vacuuming of the stair, the vacuum may be deactivated yet a force may be applied by the end effector to the stair, this force can help either "push" the robotic device up the stairs or provide a counter-balancing force for navigation down the stairs.

The controller arrangement of Figure 7 has a benefit of centralised control such that disparate operations of the robotic device, such as propulsion, joint control and cleaning may be controlled together. For example, when performing a cleaning task or function, one or more forces applied by the end effector may be modulated based on feedback from one or more of the propulsion and joint control systems. For example, a force may be reduced or increased dependent on how the robotic device is moving within the environment.

Figures 8A and 8B respectively show a cut-away of a side and a front cross-section for a fourth example robotic device 800. Figures 8A and 8B show how a control system, such as the example control system of Figure 7, may be coupled to physical components of a robotic device. As per previous examples, the two least significant digits of the reference numerals indicate correspondence with features of the first example robotic device 100 shown in Figures 1A to 1D.

The form factor of the robotic device shown in Figures 8A and 8B is particularly compact and so of particular utility in domestic environments.

Figure 8A shows a cut-away behind one of the tri-star wheels. A drive system 830 comprises a drive shaft 835 for powering a central gear of a tri-star wheel, such as central solar gear 410. The drive system 830 is mounted within a body 840. The body 840 comprises a chassis.

A shoulder joint 860 is mounted on the outside of the body 840 to control at least an angular position of upper arm link 818.

Figure 8B shows more detail of how the components shown in Figure 8A may be arranged with respect to the body 840. In this example, there are two drive systems 830 that control a tri-star wheel on either side of the body 840 via drive shafts 835. These drive systems 830 are shown coupled by a drive axle 870, although in other examples a differential drive with separate motors may be provided. Figure 8B also shows a cleaning system 850 that is also mounted with the body 840. For example, the cleaning system 850 may comprise a vacuum system and as such comprise a removable collecting unit for dust and particle matter. The propulsion system comprising components 830, 835 and 870 and/or the shoulder joint 860 may be arranged to accommodate the cleaning system 850. Other components of the fourth example robotic device 800 such as battery and power units, control boards etc. are not shown for clarity but may be designed according to the constraints of each proposed implementation.

Figures 9A to 9D show a number of variations for a robotic device comprising a set of tri-star wheels and an actuated robotic arm.

Figure 9A shows an example 900 of a shoulder joint 902 that is mounted on a top of a body 904 of a robotic device. The shoulder joint 902 may be used to implement the shoulder joint 160 in Figures lA to 1D. The shoulder joint 902 moves a link 906 (such as upper arm link 118 in Figure 1A) in at least one direction 908 (i.e. one rotational degree of freedom). In one case, the shoulder joint 902 may comprise a ball joint or an additional actuator to rotate the joint within the upper plane of the body 904 Figure 9B shows a fifth example robotic device 920. The fifth example robotic device 920 uses the shoulder joint 902 of Figure 9A and has an elongate body with two tri-star wheels 922, 924 per side (four in total on both sides). An actuated robotic arm 926 may be moved via at least the shoulder joint 902. The fifth example robotic device 920 may be suitable for larger cleaning operations, e.g. in a commercial or industrial building, while still retaining the abilities of the previously described examples.

Figures 9C and 9D are respectively a side view and a front view of a sixth example robotic device 930. The sixth example robotic device 930 has two tri-star wheels: a front tri-star wheel 932 and a rear tri-star wheel 934, as well as an actuated robotic arm 936. The tri-star wheels 932, 934 in this case comprise outer rotating wheels that extend across a width of a body 942 of the sixth example robotic device 930. The tri-star wheels 932, 934 are mounted between a support member 944 that extends the length of the body 942. In other examples, the support member 944 may comprise a plurality of support members. The body 942 also has a shoulder joint 944 that is used to control a position of the actuated robotic arm 936. The shoulder joint 946 is similar to the shoulder joint 902 of Figure 9A. Each of the front and rear tri-star wheels may rotate 952, 954 about an axis perpendicular to the support member 944, e.g. rotate within the plane of Figure 9C and out of the plane of Figure 9D. Each tri-star wheel has two lateral tri-spoke hubs 956 at either end, e.g. neighbouring the support member 944. This is best seen in Figure 9D. Three elongate outer wheels 962 extend across the width between the lateral tri-spoke hubs 956. These may be driven by a gearing arrangement similar to that shown in Figure 4 within one or both of the lateral tri-spoke hubs 956. A gear chain may be provided within the support member 944 to provide torque to a central solar gear such as 410 from one or more motors mounted within the body 942. The example of Figure 9D also shows how the shoulder joint 946 may comprise a ball joint to move upper arm link 966 in direction 968, e.g. across the body 942 as well as pivoting along the length of the body 942.

Figure 10 is a flow diagram showing a method of navigating a set of discontinuous surfaces with a robotic device according to an example. The method may be a method for performing a stair climbing procedure as shown in Figures 2A to 2D, or another procedure that allow navigation of an obstacle. The method may be implemented by the controller 720 of Figure 7.

At step 1010, a set of tri-star wheels of the robotic device are used to propel the robotic device in a direction of travel along a surface. For example, this may comprise applying a torque to a set of outer rotating wheels that are in contact with a substantially horizontal surface such as or 274. Step 1020 then occurs during movement across a discontinuity along the surface. For example, this may comprise an obstacle that extends upwards from the surface, such as the substantially vertical surface 272. In one case, a restricted movement may be detected, e.g. using one or more sensors such as accelerometers, gyroscopes, torque sensors, and/or rotation sensors. In one case, restriction of movement for a leading outer wheel or rotation of a tri-spoke hub may be detected. In this case, step 1020 comprises applying a force with an actuated robotic arm mechanically coupled to the robotic device to a portion of the surface to assist the movement. For example, this may comprise using the actuated robotic arm to push against a nearby surface as shown in Figures 2A to 2D.

The direction of travel may be any direction within an environment and may include directions that are "up" or "down" a set of stairs. The force may be applied to any location surrounding the robotic device. For example, the force may be applied in front of the robotic device within the direction of travel, behind the robotic device within the direction of travel and/or to the side of the robotic device within the direction of travel. During movement the location where the force is applied may vary. This may be performed based on considerations of a task to be performed (e.g. a cleaning task) and/or based on kinematic considerations (e.g. how best to stabilise the robotic device). The force may be applied to any surrounding surface, e.g. may be applied to surrounding objects such as stair bannisters as well as substantially vertical or non-horizontal surfaces.

In one case, the robotic device comprises an autonomous vacuuming device and the discontinuity comprises a stair or a step. In one case, applying a force with the actuated robotic arm comprises, during contact between a wheel portion of at least one of the set of tri-star wheels and a discontinuous first surface, applying a force to a second surface situated behind the robotic device in the direction of travel with the actuated robotic arm. For example, this may be performed as the robotic device climbs up and cleans a set of stairs. In other cases, e.g. when coming down a set of stairs, the force may be applied to a second surface situated in front of, or to the side of the robotic device. A cleaning function may be performed while applying the force, such as vacuuming the surface the force is applied to. In one case, impedance control may be used to adjust the force that is applied, e.g. by adjusting a torque applied at one or more joints within the actuated robotic arm.

Certain examples described herein provide a form factor for a robotic device that uses a tri-star wheel system in combination with a robot arm. In one case, the robotic device is an autonomous vacuum cleaner and a vacuuming head is mounted on an end effector of the robotic arm. Other tools may also be interchangeably attached. The tri-star wheel system provides good performances in climbing big obstacles, such as stairs. In an autonomous vacuum cleaner example, while the robotic device is climbing a set of stairs, the vacuuming head may be used to vacuum the stairs and at the same time ensure stability. Moreover, the robot arm can use impedance control to actively help the robotic device climb the stairs Depending on the specific design, tri-star wheels may be configured to climb obstacles that are up to 80% of the tri-wheel height, versus 30% of the height (e.g. diameter) of comparative non-tri-star wheels. Moreover, having at least two tri-star wheels on the two sides of a body or base provide at least four contact points, which enables stable contact surface with the ground. Exploiting this fact, the robotic arm can be used also for "off-floor" operations like vacuuming an armchair, or tidying a coffee table. The same principle can be also exploited for tool exchange operations, e.g. switching between two different types of vacuuming head, or substituting the vacuuming head with a gripper.

The above examples are to be understood as illustrative. Further examples are envisaged. Any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMS1. A robotic device comprising: an actuated robotic arm comprising an end effector and one or more powered joints, the position of the end effector relative to the robotic device being controllable to perform at least one task; and a propulsion system comprising: a drive system, and a set of tri-star wheels coupled to the drive system.
2. The robotic device of claim 1, comprising: a cleaning system, wherein the actuated robotic arm is coupled to the cleaning system and the task comprises at least one cleaning task.
3. The robotic device of claim 2, wherein the cleaning system comprises a vacuum system, and wherein an aperture at the end effector of the actuated robotic arm is maintainable at a low pressure using the vacuum system
4. The robotic device of any one of the previous claims, wherein the actuated robotic arm comprises a plurality of joints.
5. The robotic device of any one of the previous claims, wherein the actuated robotic arm has three to six degrees of freedom.
6. The robotic device of any one of the previous claims, wherein the set of tri-star wheels support the robotic device upon a surface and the actuated robotic arm is configured to perform the at least one task above or below the surface.
7 The robotic device of any one of the previous claims, comprising: a chassis housing at least the propulsion system, wherein the actuated robotic arm is mechanically coupled to the chassis, and wherein the set of tri-star wheels comprise a pair of tri-star wheels arranged on either side of the chassis.
8. The robotic device of any one of the previous claims, wherein the end effector comprises an interface for removably mounting a plurality of tools.
9. The robotic device of claim 8, wherein the plurality of tools comprise one or more of a gripper, a brush and a vacuuming head.
10. The robotic device of any one of the previous claims, comprising: a controller electronically coupled to the propulsion system and the actuated robotic arm, wherein the controller is configured to control at least the actuated robotic arm.
11. The robotic device of claim 10, wherein the controller is configured to control the actuated robotic arm to assist the propulsion system when navigating discontinuous surfaces.
12. The robotic device of claim I I, wherein the controller is configured to use the actuated robotic arm to apply a stabilising force to a surface behind the robotic device during forward motion using the set of tri-star wheels.
13. The robotic device of any one of claims 10 to 12, wherein the controller is configured to apply impedance control to adjust the one or more powered joints based on a force applied to the end effector.
14. A method of navigating a set of discontinuous surfaces with a robotic device, the method comprising: driving a set of tri-star wheels of the robotic device to propel the robotic device in a direction of travel along a surface; and during movement across a discontinuity along the surface, applying a force with an actuated robotic arm mechanically coupled to the robotic device to a portion of the surface to assist the movement.
15. The method of claim 14, wherein the robotic device comprises an autonomous vacuuming device and the discontinuity comprises a stair or a step.
16. The method of claim 14 or claim 15, wherein applying a force with the actuated robotic arm comprises, during contact between a wheel portion of at least one of the set of tri-star wheels and a discontinuous first surface, applying a force to a second surface situated behind the robotic device in the direction of travel with the actuated robotic arm.
17. The method of any one of claims 14 to 16, comprising performing a cleaning function before, during or after applying the force.