GB2624655A

GB2624655A - Actuators

Info

Publication number: GB2624655A
Application number: GB2217552.5A
Authority: GB
Inventors: Mohammad Abdelkhalick; Breeze Nicholas; A Axinte Dragos; D Norton Andrew
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2022-11-24
Filing date: 2022-11-24
Publication date: 2024-05-29
Also published as: GB202217552D0

Abstract

An actuator 20 for a continuum robot comprises a dielectric elastomeric material (DEA) 22 wrapped around a central compression spring 21 having at least one pair of opposing electrodes positioned either side of the dielectric elastomer and a controllable voltage source which applies a voltage to the electrodes to cause a change in the length of the actuator 20. The dielectric elastomer 22 may comprise an acrylic or a silicone and the electrodes may comprise graphene, carbon grease or carbon nano tubes. The actuator 20 may be provided with a resiliently deformable skin and an anchor point for mounting a tendon or pulley. A continuum robot arm may comprise an active section having a plurality of joints manipulatable in two dimensions, with each joint of the plurality of joints being orthogonally offset with respect to the plane of motion, the distal end of the continuum robot having an end effector and a passive section comprising a plurality of actuators 20, with the tendons for driving a joint being coupled to a respective actuator. The actuators may be mounted in series (30a, 30b, 30c figure 3) within the robot arm and voltage may be provided from an external source via cable (34a, 34b, 34c). End caps 23 may be provided with interconnecting features that engage with those of neighbouring actuators 20.

Description

Actuators

Overview of the disclosure

The disclosure relates to a soft actuator for use in a continuum arm robot. In particular, the disclosure relates to a continuum arm robot utilising dielectric elastomer materials within the actuators.

Background of the disclosure

Continuum arm robots are used in a number of inspection and repair processes. These processes usually occur in difficult to reach areas where human operators are unable to access without disassembling the equipment which can potentially be dangerous or time consuming. The benefits of using a flexible robot are the dexterity of the arm that allows it to manipulate its body shape around obstacles whilst still maintaining the strength to perform the task. Due to these benefits continuum arm robots are also used in fields outside of engineering such as in surgery, humanitarian rescue within collapsed buildings and in engineering fields such as repair of gas turbines as well as in pipes and conduits in the energy and telecommunications industries among many others.

One of the issues with continuum robots is their requirements for expensive actuator packs to control the positioning and movement of the active part of the continuum arm robot. These actuator packs comprise a large number of electronic motors or servo drives that manipulate the tendons that drive the sections of the arm. As well as being expensive the actuator packs are large and need to be held away from the robotic arm, which requires the use of a long passive section of robot if the robot needs to perform the task at a distance from the access point. This passive section adds mass and complexity to the robot and presents a greater chance of damage to the robot arm. Consequently, it would be desirable to produce an alternative actuator design.

Summary of the disclosure

According to a first aspect of the disclosure there is provided an actuator for a continuum robot comprising a central compression spring, and a dielectric elastomer having at least one pair of opposing electrodes positioned either side of the dielectric elastomer, the dielectric elastomer being wrapped around the central compression spring and a controllable voltage source which applies a voltage to the electrodes to cause a change in the length of the actuator.

The actuator may be provided with an anchor point for mounting a tendon or pully.

There may be provided 2-4 pairs of electrodes mounted coupled either side of the dielectric elastomer layer.

The voltage source may be configured to provide voltage to the pairs of electrodes individually.

The dielectric elastomer may comprise one of the following groups: Silicones or acrylics.

The electrodes may comprise one of the following: graphene, carbon grease or carbon nano tubes.

The actuator may be provided with end caps at proximal and distal ends of the actuator According to a second aspect of the disclosure there is provided a continuum robot arm comprising an active section having a plurality of joints manipulatable in two dimensions, the with each joint of the plurality of joints being orthogonally offset with respect to the plane of motion, the distal end of the continuum robot having an end effector and a passive section comprising a plurality of actuators as discussed above, with the tendons for driving a joint being coupled to a respective actuator.

The actuators may be provided with a resiliently deformable skin around the outside of the actuators.

The plurality of actuators may be mounted in series within the robot.

The voltage source may be mounted external to the robot and the voltage is supplied to the robot via a plurality of cables.

The cabling or supply for the end effector may be provided through the centre of the spring 20 section.

The plurality of actuators may be mounted into actuator sections containing a discrete number of actuators within the actuator section, and each actuator driving its own cable for a joint, such that the actuator sections drive a plurality of joints in the active section.

At least one spring within the plurality of actuators may have a different spring constant.

At least one spring within the plurality of actuators may have a different length.

The actuators may be provided with end caps according to the above discussion, the end caps being provided with interconnecting features so that they can engage with those of neighbouring actuators.

The actuators may be connected modularly, so that they can be interchanged.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

Brief discussion of the figures Embodiments will now be described by way of reference only, with reference to the figures in which: Figure la presents a prior art example of a cut away of a continuum arm robot; Figure lb shows an example of the joints of a continuum arm robot; Figure 2a presents an example of an actuator section for a continuum robot according to the

present disclosure;

Figure 2b presents an example of an actuator section according to the present disclosure formed; Figure 3 presents an example of linked actuators according to the present disclosure; Figure 4a presents an example of an actuator having multiple sections and being in its normal state; Figure 4b presents an example in which all of the sections within the actuator have been activated; Figure 5 presents an example of a continuum robot incorporating the actuators of the

present disclosure.

Summary of the disclosure

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art Figure la presents a prior art example of a cut away of a continuum arm robot. The prior art continuum arm robot comprises the continuum arm robot portion 101 permanently integrated and extending out from the actuator pack 102. The actuator pack 102 contains a plurality of independent actuators 103. These actuators are used to modulate the tension within the tendons that run through the continuum arm 101. The tendons are associated with joints within the arm; each of these joints is designed to move in response to a tensioning or relaxing of the tendon associated with the joint. This tensioning or relaxing of the tendon therefore causes a contraction or extension of the joint; this, allows the continuum arm to bend. The actuator pack is shown being positioned on a rail or support 104, which is positioned close to the component that is to be inspected. The actuator is also provided with a plurality of power and signal cables 105 that are used to power and address the actuators.

The individual signals across the range of actuators provide control of the joints such that the continuum arm 101 can be directed. Not shown in figure 1, is that there is also a need for an operator with a computing device that is linked to the actuator to control movement of the continuum arm and to perform the desired task. As the continuum arm robot is permanently integrated into the actuator pack a complete separate set up is required if the process requires that the tool is changed. This increases the operating cost for the application. The computing device that is connected to the prior art actuator may be any suitable computing system such as a laptop computer featuring the requisite operating software for the robot and a control input such as a joystick, which allows the continuum arm to be controlled.

Figure lb shows an example of the joints of a continuum arm robot. The arm comprises multiple joints, which require at least 2 cables per joint. For example, a system having three joints, each having 4 tendons per joint will require 12 actuators to drive the arm. To increase the number of joints either the number of actuators needs to be increased or the number of tendons per joint needs to be reduced. Highlighted joints 106, 107, 108 are able to be manipulated to move in three dimensions. The joints are configured so that joints 106 and 108 are able to be able to flex in the same plane relative to the centre of the arm, whilst the plane that joint 107 is able to move in is offset by 900 to joints 106 and 108. It is through this repeating configuration of alternating joint angles, each of which results in the movement in different orthogonal plane, that allows the arm to be manipulated in three dimensions. Each joint within the arm has a limit to the amount they are able to flex; this is defined by the design of the arm and the materials that are used. The limit of flex in each joint sets the characteristics of the robot such as the minimum bending radius and the torque that is required to cause a resultant change of angle within the joint. At the end of the arm there is positioned a tool or probe that is designed to perform one or more functions, once the continuum arm is in position. The heads of the continuum arm robots are often provided with optical systems so that the operator is able to view the head as it is being inserted into the component and to control the head as it performs its tasks. The optical system is also frequently coupled to an illumination system. The control cables for the tool/end effector, electrical power connectors to the illuminations system, and optical cables are usually able to run through the centre of the joints within the continuum arm. This has the benefit of protecting the cables form any potential damage. All of these components as well as the arm structure are permanently coupled to the actuator; this means that if the arm fails or has a problem the entire continuum arm robot needs to be replaced.

Figure 2a presents an example of an actuator 20 for a continuum robot according to the present disclosure. In this, the core of the actuator section is formed around a compression spring 21. Around the compression spring is a dielectric elastomeric material (DEA) 22. Any suitable elastomer can be used. This can be any suitable electroactive polymer. For example, these may be materials such as Silicones or acrylics. An example of such a material is 3M Very High Bonding VHB or silicone. At the tip and the base of the actuator unit end caps 23 may be present. These end caps may house the electronic connectors that are used to supply the electrodes and are attached to the ends of the elastomer before winding. The end caps can be rigid or semi-rigid. The dielectric elastomer comprises a compliant elastomer that is sandwiched between a pair of flexible electrodes. Any suitable flexible electrode can be used such as, graphene, carbon grease or carbon nano tubes, or other flexible electronic materials. Application of a voltage to the electrodes creates a pressure within the elastomer and results in deformation. The deformation causes an extension of the compression spring and thus causes a change in the length of the actuator. By attuning the electrode structure around the elastomer allows for controlled deformation such that the actuator can be manipulated in shape. The actuator is connected to a pully or cable which manipulates the movement of a joint within the active section of the robot body.

The tendons can be coupled to the actuators though connection to the end caps. This connection may be achieved through any suitable means such as, clamping or bonding. The presence of the compression spring at the core of the actuator means that when there is no voltage applied to the electrodes the actuator is forced to resort to its original form. The compression spring can be formed from any suitable material. For example, the compression springs may be formed from a plastic material. Alternatively, the compression springs may be made from a metallic material. The compression springs may have any suitable spring constant. The design allows for precise control of length of the actuator along the axial dimensions. The controlled amount of deformation allows for precise movement of the cable that manipulates the sections; this allows the continuum robot to bend and manipulate its shape with defined movements. Figure 2b presents an example of an actuator section according to the present disclosure in its formed state. In this the compression spring is not visible, but the deformable elastomer 22 and the end caps 23 are shown. The arrows show the direction of motion that the actuator can attain.

The shape and size of the actuators means that they can be housed in an actuator pack. Alternatively, they may be housed within the robot arm itself. Such a configuration would not be possible with the current electromagnetic motor actuators that are used. Furthermore, as the spring is hollow it allows for any caballing and/or conduits to be run through the centre of the actuator to the end effector or to other sections of the robotic arm. The actuators can be placed within an outer skin so as to protect them from damage from external factors that may be present within the work environment where the robotic arm is due to work. The end caps 23 may have a seal or a joint so that the actuators can be removed or swapped out, so that the performance characteristics can be changed or to allow for ease of repair.

A plurality of actuators 30a, 30b and 30c may be strung together to provide greater control and movement of a plurality of tendons. An example of such a system is provided in figure 3. This shows an arm section having three actuators within the body. Each actuator may be broken into a plurality of electrode sections. In the example presented in figure 3 the actuator is separated into three electrode sections. This increases the control of the force applied to the actuator. The electrode sections can be wired in parallel with controllable switching means so that each actuator can be individually addressed. This allows for control of the voltage provided to the actuator and as such provides a defined amount of movement of each actuator. Each actuator 30a, 30b and 30c is connected to a cable 34a, 34b and 34c to allow the actuator to be provided with a controlled voltage. Each actuator may be connected to a cable or a pully to allow it to control a joint within the robot arm. The actuators may be positioned so that they have a small space between the actuators to allow them to change in size. Because the actuators are constructed of an elastomeric material positioned about a spring it means that the body of the robot is still able to conform to the working environment.

Each actuator may have a cable that runs through it. The cables are connected to an actuator controller that may be provided within the robot body or external to the robot body. The actuators may be connected to an actuator controller. The actuator controller supplies a voltage to each of the actuators and the electrode sections. This voltage may be calculated from a computer program. The program being configured to allow an operator to control the motion of the robot, by providing real time changes to the voltage applied to the actuators to allow the active part of the robotic arm to deform in the desired way. Consequently, as the operator inputs a desired motion path or instruction to the arm the computer program the program determines how much each joint of the robot needs to bend and what is the required voltage to be applied to the actuator to achieve this deformation. The computer program then determines the voltage levels that need be changed to in order to produce the amount of movement that the actuator needs to undergo. Figure 3b shows an example of the robot arm being deformed and bent such that it can sit within a path that the continuum arm traces. The use of such a system allows for a continuum robot that is easily deployable within a number of environments with limited equipment. The deformable and flexible nature of the actuators means that the actuator section of the robot can also deform and as such can replace a passive section of the robot if the robot arm is long enough. There may be any suitable numbers of actuators placed within the arm. Furthermore, due to the reduced cost, size, and weight over electromagnetic motor actuators means that a larger number of actuators may be applied to the robot, as such, this would provide an arm with greater control or a greater number of degrees of freedom.

Figure 4a presents an example of an actuator 40 having multiple sections and being in its normal state. In this there is no voltage applied to the electrodes on the actuator sections and the size of the actuators is defined by the construction length about the spring at the centre. Due to there being no force applied by the electrodes there is no change to the structure of the actuator under these conditions. Consequently, the cables of the continuum arm that are connected to the actuator are at their normal tension when the actuator is in this state. Figure 4b presents an example in which all of the sections within the actuator 40 have been activated. In this case a voltage has been applied to electrodes about the elastomers this has resulted in an increase in length of the actuator sections within the actuator. The direction of the force applied by the actuator is represented by the arrow. In such a state there is an increase in the tension applied to the cables of the continuum arm. Variation of the applied voltage results in different amounts of force applied by the electrodes. Thus, through control of the applied voltage it is possible to provide a controlled deformation of the actuator, which provides a controlled amount of movement to the tendons. Each tendon may be connected to its own respective controlled voltage supply.

Figure 5 presents an example of a continuum robot incorporating the actuators 50a, 50b, and 50c connected to cables 54a, 54b and 54c which provide the voltage to the actuator. In this the robot comprises an active section and a passive section. The active section comprising a plurality of joints being orthogonally offset with its neighbour in respect to the plane of movement. The active sections provide the requisite number of degrees of freedom for the arm and the end effector to operate in the desired function. The DEA actuators are provided within the passive section of the continuum arm robot. Each actuator being connected to a respective joint of the active section. The actuators may be mounted individually, or in actuator sections comprising a discrete number of actuators linked together. A tendon or pully is mounted from an actuator to at least one respective joint within the active section. The caballing for the tendons or pulleys may run around the outside of the actuators. Alternatively, the tendons or pulley cables may be routed through the centre of the actuators in the channel provided by the spring. The caballing or conduit/ducting required by the end effector may be ran through the channel provided by the spring at the centre of the actuators. The end effector may be any suitable tool. For example, this could be a vision system incorporating a camera, or multiple cameras, the end effector, may comprise a fluid supply or vacuum system, the end effector may comprise a rotary tool. The voltage supply for the actuators may be provided within the robot. Alternatively, the voltage supply may be provided external to the compliant robot body. The passive section may be provided with a skin to protect the actuators. The actuators may be provided with end caps. The end caps may be provided with engagement features to allow them to engage a positionally lock with respect to their neighbouring actuators. The engagement features may also be provided with electrical coupling means to allow the actuator to receive the voltage required. The skin may comprise a resiliently deformable membrane that covers the actuators. The skin may cover all the actuators. Alternatively, the skin may only cover the actuator between the endcaps if provided. The latter allowing a quickly interchanging modular construction for the continuum robot. At least one actuator may be provided with a spring having a different spring constant and/or a different length; this providing a non-linear response from the different actuators.

There may be any suitable number of actuators within the arm of the continuum robot so that they can provide movement to the cables that drive the joints. The number of actuators will provide the level of control for the number of degrees of freedom provided by the joints. Because the actuators are the same, they provide a modular design which allows for broken or faulty actuator sections to be switched out. The modular design allows for a number of modifications to be made to the actuators to change their design and working operation.

Such modifications can be tailored to the needs of the robot and the actuators may be swapped for different purposes. Possible modifications may be made to vary the amount of manipulation that the actuator can sustain. This can therefore change the Minimum and/or Maximum amount of possible actuation that can be achieved. By tailoring the material that the dielectric elastomer is made from it is possible to adjust the amount of force that the actuator can produce. This tailoring can allow for the actuators to have a defined minimum and/or maximum force that the actuator can produce. It is also readily possible to change the nominal Length of each section, such that it is able to perform its desired task. Depending upon the number of actuators that are present it is possible to determine the total length of the robot arm. The actuators can be of any suitable size, and as such they can be scaled to any nominal diameter that is required for the purpose. Therefore, the size of the robot can be determined by the actuator diameter. As such, the present provides a scalable means of controlling a robot of any diameter and/or length. By not being constrained by length increases the usability of the robot arm. This allows for more detailed in-situ inspections and repairs/treatment. As discussed previously, due to the centre of the actuators being hollow the design has the ability to run further cables and/or tubes through its central column to supply power to desired end effector. Furthermore, the proposed actuators remove the need for a costly external actuation pack. This means that the cost of the robot will decrease allowing the robots to be tailored to specific tasks with operators having multiple robots to perform all their needs.

The advantage of the present design means the design can be tailored to suit the purpose of the task to be performed to a greater extent than classical electromechanical actuators. As such, the assemblies can be made modular, so that they can be swapped and changed to allow for changes in use. This means that Modular Rolled DEA Assemblies can be scaled up or down depending on the specific application. This can be achieved by adding or removing Rolled DEA sections to increase or decrease the amount of actuation. Additionally or alternatively, the amount of displacement produced may be tailored by changing the length of the central spring within the DEA. This is because the longer the spring the larger the active area that DEA can have. The rolled DEA Sections can also be scaled depending on the specific application by increasing or decreasing the number of rolls to increase or decrease the amount of force output from the actuators along with the amount of actuation required. Additionally or alternatively, the force produced and the displacement achieved can be varied by using central springs with different spring constants. If multiple DEA spring rolls are used in parallel and/or in series, then springs with different spring constants can be used to cause nonlinear displacement curves. Additionally or alternatively, another method of modifying the properties can be achieved by changing the number of spring roll DEA assemblies in series to change the number of pully cables being controlled depending on the specific application.

Any of these changes can be made on their own or in combination with each other to produce different force and displacement outputs or levels of control to tailor the robot arm to the specific application required of the snake like robot. The diameter of the DEA spring rolls and subsequently the whole assembly can also be scaled up or down in size depending on the size of the snake like robot that requires actuating.

It will be understood that the invention is not limited to the embodiments above described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

Claims 1. An actuator for a continuum robot comprising a central compression spring, and a dielectric elastomer having at least one pair of opposing electrodes positioned either side of the dielectric elastomer, the dielectric elastomer being wrapped around the central compression spring and a controllable voltage source which applies a voltage to the electrodes to cause a change in the length of the actuator.
2. The actuator according to claim 1, wherein the actuator is provided with an anchor point for mounting a tendon or pully.
3. The actuator according to claim 1 or claim 2, wherein there is provided 2-4 pairs of electrodes mounted coupled either side of the dielectric elastomer layer.
4. The actuator according to claim 3, wherein the voltage source is configured to provide voltage to the pairs of electrodes individually.
5. The actuator according to any preceding claim, wherein the dielectric elastomer comprises one of the following groups: acrylics or Silicones.
6. The actuator according to any preceding claim, wherein the electrodes comprise one of the following: graphene, carbon grease or carbon nano tubes.
7. The actuator according to any preceding claim, wherein the actuator is provided with end caps at proximal and distal ends of the actuator
8 A continuum robot arm comprising an active section having a plurality of joints manipulatable in two dimensions, the with each joint of the plurality of joints being orthogonally offset with respect to the plane of motion, the distal end of the continuum robot having an end effector and a passive section comprising a plurality of actuators as claimed in any one of claims 1-7, with the tendons for driving a joint being coupled to a respective actuator.
9. The continuum robot according to claim 8, wherein the actuators are provided with a resiliently deformable skin around the outside of the actuators.
10. The continuum robot according to claim 8 or claim 9, wherein the plurality of actuators are mounted in series within the robot.
11. The continuum robot according to any one of claims 8 to 10, wherein the voltage source is mounted external to the robot and the voltage is supplied to the robot via a plurality of cables.
12. The continuum robot according to any one of claims 8 to 11, wherein the cabling or supply for the end effector is provided through the centre of the spring section.
13. The continuum robot according to any one of claims 8 to 12, wherein the plurality of actuators are mounted into actuator sections containing a discrete number of actuators within the actuator section, and each actuator driving its own cable for a joint, such that the actuator sections drive a plurality of joints in the active section.
14. The continuum robot according to any one of claims 8 to 13, wherein at least one spring within the plurality of actuators has a different spring constant.
15. The continuum robot according to any one of claims 8 to 14, wherein at least one spring within the plurality of actuators has a different length.
16. The continuum robot according to any one of claims 8 to 15, wherein the actuators are provided with end caps according to claim 7, the end caps being provided with interconnecting features so that they can engage with those of neighbouring actuators.
17. The continuum robot according to any one of claims 8 to 16, wherein the actuators are connected modularly, so that they can be interchanged.