Patent Application
20220297287
The present invention relates to a tendon tension sensing apparatus for a mechanical effector device. More particularly, the present invention relates to a tendon tension sensing apparatus for a robot hand.
The present invention also relates to a clutch mechanism for a mechanical effector device. More particularly, the present invention relates to a clutch mechanism for a robot hand.
It is desirable to use robotic devices in many industries, and there is a wide range of known devices that closely mirror or mimic the functionality of the human hand, as well as robot hands that are inspired by the human hand, but which have differing numbers of digits and different functionality. An example of a known type of robot hand is described and shown in U.S. Pat. No. 7,168,748.
The human hand is capable of numerous movements over a wide range and over different axes. In addition, the human hand is capable of gripping objects over a wide range of different sizes, using a wide range of forces from very delicate to very strong. The vast range of movements and functionality are difficult to accurately reproduce, since each additional axis or range of movement usually requires the addition of a further joint or joint assembly within the structure of the robotic hand. Each separate joint or joint assembly requires it's own power supply and control mechanism, and these need to be connected to the joint and through the overall structure, and correctly positioned, so as to avoid interference with any intervening or neighbouring elements. This usually results in a highly complex arrangements of wires and cables, both for power delivery and sensing, and also for transmission of movement forces (tendon cables or wires). The number of these wires and cables, plus associated elements, increases for every additional joint/joint assembly. This results in robotic hands being complex to produce and usually also bulky, which can in turn reduce the overall dexterity of the robotic hand.
In order to get overall motion or force in the correct or desired direction, it is necessary to provide a precise level of force to multiple tendons within the hand, so that movement of a number of individual joints is resolved into the correct overall direction and force. It is therefore necessary to accurately measure the force in each individual tendon, so that the overall force (and therefore movement) is resolved correctly. One known way of measuring the tension in a tendon is to pass this through a relatively sharp bend or corner of around 90 degrees. This allows force to be measured through a relatively discrete point, which allows accurate measurement. However, corners create wear points, and as the tendons pass backwards and forwards over the corner in use, they quickly become worn and can fail more rapidly (in fewer cycles) than is desirable.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
It is an object of the present invention to provide a tendon tension sensing apparatus for a mechanical effector device which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.
It is a further object of the present invention to provide a tendon tension sensing apparatus for a robot hand which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.
It is a yet still further object of the present invention to provide a clutch mechanism for a mechanical effector device which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.
It is a yet still further object of the present invention to provide a clutch mechanism for a robot hand which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.
The term “comprising” as used in this specification and indicative independent claims means “consisting at least in part of”. When interpreting each statement in this specification and indicative independent claims that includes the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner.
As used herein the term “and/or” means “and” or “or”, or both.
As used herein “(s)” following a noun means the plural and/or singular forms of the noun.
Accordingly, in a first aspect the present invention may broadly be said to consist in a clutch mechanism for a mechanical effector device, comprising: a reel configured for winding and unwinding a tendon around the reel; a base configured to connect to and rotate with a motor for rotation of the base around an axis; the reel and base further configured for alignment with and rotation around a common axis of rotation, the inner ends of the reel and base mutually castellated and interlocking so that the base and reel rotate together; the castellations configured to ride up and over one another to allow independent rotation of the reel and base if an un-resolvable rotation force is encountered.
In an embodiment, the clutch mechanism further comprises a spring, the spring configured to provide a reaction force against the reel is response to movement of the reel along the axis of rotation away from the base.
In an embodiment, the castellations have sloped sides, the dimensions of the reel and base, the angles of the sloped sides, and the strength of the spring adjusted to provide a desired maximum disengagement force between the reel and base.
In an embodiment, there are three castellations on each of the reel and base.
In an embodiment, each of the castellations on one of the reel or the base further comprises a ball bearing located within the castellation, the outwardly-facing part of the bearings fitting within corresponding indentations formed in the other of the reel or base.
In a second aspect, the invention may broadly be said to consist in a tendon tension sensing apparatus for a mechanical effector device, comprising: three pulley wheels arranged linearly relative to one another with the central pulley wheel offset from the pulley wheels each side, the pulley wheels configured to allow a tendon to pass thereover and operate in use, the tendon forming the two shorter sides of a triangle with an apex that runs over the centre pulley wheel, the base of the triangle formed by a line that runs tangentially between the outer pulley wheels; a load cell connected to the central pulley wheel, the load cell configured to measure the deflection of the central pulley wheel when a force is applied to the tendon.
In an embodiment, the rotational axes of the pulley wheels are arranged substantially in parallel to one another.
In an embodiment, the load cell comprises a substantially solid body and a strain gauge connected to the body, the strain gauge configured to provide displacement data in real-time to the controller of the mechanical effector device.
In an embodiment, the load cell is configured to measure the linear force or movement of the central pulley perpendicular to the base of the triangle.
In an embodiment, wherein the dimensions of the pulleys, the offset and the distances between the pulleys are chosen to minimise as far as possible the offset or angling of the tendon.
With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
Further aspects of the invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings which show an embodiment of the device by way of example, and in which:
Embodiments of the invention, and variations thereof, will now be described in detail with reference to the figures.
A robot hand 1000 is shown in
The amount of force transmitted depends on the tension or ‘pull’ on/through the tendon, which is in turn transmitted to the digits of the hand, these then exerting a gripping force on a grasped object. It is important that this tension can be accurately and repeatably measured, so that the amount of force exerted on a grasped object can be accurately calculated. It is also important that the tendon should have as long a lifespan in use as possible. That is, that is should potentially be capable of hundred of thousands or millions of uses, or separate cycles of tension and release.
A sub-assembly 1001 of a robot hand is shown in
Clutch
As noted above, in order to get overall motion or force from the hand in the correct or desired direction, it is necessary to provide a precise level of force to multiple tendons within the hand, so that movement of a number of individual joints is resolved into the correct overall direction and force. It is possible that in use these forces do not fully resolve in the desired manner, or that there is in certain circumstances a miscalculation of the distances and forces required, particularly when the hand is operating within changing surroundings, with semi-static but moveable external elements. This can result in the hand or elements of the hand impacting and being forced against a surface or other element, with feedback being insufficient and/or not provided rapidly enough for immediate reversal or disengagement. This can cause excessive force to be exerted on the tendon or tendons, as the motor attempts to resolve the initial commands by continuing to apply force or by applying increasing force, but with the hand elements physically blocked from resolving these.
The present invention comprises a clutch or clutches within an effector such as a robot hand, so that if this situation arises, the tendons are not subject to a force sufficient to cause damage or destruction (e.g. snapping of the tendon).
As shown in
The common/connected ends of the reel and base are configured as a clutch. The connecting ends of the base 103 and the reel 102 are mutually castellated, the castellations 107a, 107b on the reel 102 and base 103 respectively having sloped or angled sides, as shown in the two alternative embodiments of
In normal use, the castellations 107a, 107b fully interlock so that as the tendon 105 moves backwards and forwards, the base 103 and reel 102 both rotate together. However, if there is an issue, and increasing but un-resolvable force is being applied to the tendon 105 (for example, if that part of the hand 1000 to which it is connected is jammed against a surface and is attempting to move through the surface to resolve it's position programming), then the clutch 101 will ‘slip’ in order that damage to the tendon 105 and potentially other elements is prevented. The reel 102 and base 103 will move relative to one another so that the castellations 107a, 107b start to ride up and along and over each other. The base 103 will be forced back against the coil spring 106.
If the force is strong enough to overcome the inherent reaction force provided by the castellations 107 and the spring 106, then the castellations 107 will ride up and over each other, allowing the reel 102 to rotate and the tendon 105 to move, to release the force on the tendon 105.
The size of the elements (e.g. the reel and base 102, 103), the angles of the castellations 107, and strength of the spring 106 can all be calculated to provide the desired release force or trigger force—that is, the maximum force at which the clutch 101 will disengage.
That is, the tendon 105 transmits a force on to the reel 102 which converts to a torque of the reel 102 when this torque is transmitted, via the castellations, from the reel 102 to the base 103, and then in turn to the motor. In a similar fashion, the motor generates a torque that is transmitted to the base 103 and in turn to the reel 102 which generates a tension force in the tendon.
If, during rotation in either direction the torque exceeds the torque that the castellations can transmit, they will begin to separate. The maximum level of torque that can be transmitted before these two elements begin to separate is governed by the force of the spring 106. The spring tension can be adjusted by increasing or decreasing the gap in which the spring 106 sits, pre-compressing the spring 106 to a greater or lesser extent. This is achieved by rotating the end elements 110, which are threaded to facilitate this adjustment. In the preferred form, once this adjustment is complete the elements 110 are then locked in the required position with thread locking adhesive. However, other means could be employed to provide this adjustment. By spring selection and adjusting the pretension of the spring the clutch can be set to disengage at a specific torque or tendon tension, for example a tendon tension of approximately 50 newtons is common in the current embodiment of the invention.
The use of a clutch allows the use of a powerful motor without having to change other elements to compensate (e.g. stronger material for the tendons).
The use of the castellations also provides a ‘pre-slip signal’. As the base and reel start to ride up, this can be detected, and used to provide feedback to the controller.
Additionally, this partial slip condition serves to soften transient force spikes. When high peak load is caused by for example high motor acceleration some of that energy is absorbed into the spring reducing the wear on the tendon from unnecessary high peak loads. Thus, even without completely disengaging the clutch can absorb some peak loads reducing wear on either the tendon or the motor gear depending in which direction the peak impulse load is traveling.
It should be noted that the use of ball bearings in the clutch of the present invention, and as described above for the preferred embodiment, offers an advantage over simply having castellated elements, as this allows greater precision, and therefore greater precision in the point of release/force required for release. A castellated element without ball bearings tends to require greater precision in manufacturing machining to achieve a similar result, and this can drive up the overall cost required.
The reel material is chosen to provide the correct bearing function both for the castellations to transmit torque, and also where the reel contacts the rod (not shown) that forms the axis of rotation. In use, the reel must slide along and around this rod in normal use, and as the reel disengages from the base. This sliding action needs to be reasonably low friction so as not to overly increase the torque needed to disengage the clutch.
In the preferred embodiment, the current reel diameter where the tendon wraps onto the reel is 10 mm which gives an effective radius (within which tendon tension is acting) of 5.4 mm, assuming a tendon with a diameter of 0.8 mm. For a given tendon tension of x Newtons this would become x multiplied by 5.4 newton millimetres (Nmm) thus a tendon tension of 50N would become a torque of 270 Nmm and similarly a motor toque applied through the clutch of 270 Nmm would become a tendon tension of 50N. (assuming no frictional or other losses).
However, in certain embodiments, castellated elements are preferable, and an alternative arrangement is shown in
Tendon Tension Sensor
An embodiment of the tendon tension sensor assembly 300 is shown in
As shown in
The dimensions of the pulleys, the offset and the distances between the pulleys are chosen to minimise as far as possible the offset or angling of the tendon 105—to minimise the size of the two smaller angles of the triangle described above (the angles formed between the ‘base line’ between pulleys 301, 303, and the sides 301-302, and 303-302. Any point where the tendon 105 has to ‘turn’ a corner or go through an angle creates a potential wear point on the tendon 105 which can lead to failure and/or a reduced life span. A sharper or more acute angle means that the tendon 105 has to ‘turn’ a sharper corner, and this potentially creates a greater level of wear, an increased chance of failure, and a reduction in the lifespan of the tendon 105. Therefore, the dimensions are chosen to minimise the angles as far as is practical. This reduces the tendon load and therefore reduces tendon wear as it passes over the deflection points and changes it's direction of travel.
In the preferred embodiment, the diameter of the pulley 301, 302, 303 is 10 mm. The two outer pulleys 301, 303 are set apart a distance of 90 mm, with the central pulley 302 set such that the tendon forms an equilateral triangle between the three pulleys with base angles of 3 degrees. From this geometry the resultant force acting on the middle pulley and thus transmitted to the load cell is the tendon tension multiplied by a factor of 0.1 so a tendon tension of 50N is seen as a force of 5N at the load cell. The angle of deflection can be chosen for the desired multiplication factor, such that this multiplication factor is 2 times the Sin of the angle—that is, 2*SIN(Angle).
A load cell 304 is arranged behind and connected to the central/offset pulley 302, to measure the deflection of the pulley 302 when the robot hand is in use and a force is applied to the tendon 105. The load cell 304 measures the linear force or movement of the central pulley 302, perpendicular to the base line of the triangle 301-302-303, and uses this to calculate the tension/force in the tendon 105. The load cell 304 in this embodiment comprises a solid aluminium body 305 with a strain gauge 306 applied to/connected to the body. The strain gauge 306 provides displacement data in real-time to the hardware/software controlling the robot hand, so that this can be used to calculate the required power to the motor and therefore the tension/force in the tendon 105, as required.
It has been found that the working envelope of the tendon 105 can be kept well within tolerance by choosing a small or shallow angle or shallow path, while still providing enough sensitivity to allow accurate, fast and responsive measurement of the tension in the tendon 105.
An arrangement as outlined above minimises the change of angle of the tendon 105, and therefore the frictional wear, while still providing an arrangement where bending stresses can be accurately measured (and therefore the tension in the tendon accurately calculated).
| Number | Date | Country | Kind |
|---|---|---|---|
| 1911453.7 | Aug 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/057469 | 8/7/2020 | WO |
