EP2914404A2

EP2914404A2 - Hand exoskeleton

Info

Publication number: EP2914404A2
Application number: EP13824005.6A
Authority: EP
Inventors: Yasheen BRIJLAL; Lester Ryan John; Sudesh SIVARASU
Original assignee: University of Cape Town
Current assignee: University of Cape Town
Priority date: 2012-11-01
Filing date: 2013-10-31
Publication date: 2015-09-09
Also published as: WO2014068509A3; CN104768714A; WO2014068509A2; ZA201502680B

Abstract

A hand exoskeleton device is provided having at least three robotic units. One is for attachment to the thumb and has two elements for attachment to the distal and proximal phalanges. The other two each have three elements, for attachment to the distal, middle and proximal phalanges of the index and middle fingers. The elements of each robotic unit are interconnected by suitable hardware to provide for relative angular movement of the elements about an axis of rotation that corresponds substantially to the axis of rotation of a user's interphalangeal joint movement. An actuator is associated with the interconnecting hardware to enable adjustment of the two elements in each of two opposite directions. A sensor senses the angular position or force of one element relative to the other element of each pair. A computerized controller controls movement of the elements of each pair by means of the associated actuator.

Description

HAND EXOSKELETON

FIELD OF THE INVENTION

This invention relates to a hand exoskeleton device to aid, inter alia, in handwriting rehabilitation of stroke patients and other persons having limited or impaired control over finger movements. The invention is more particularly concerned with a hand exoskeleton device that is robotically controlled to guide or assist in moving the fingers for a variety of purposes, especially handwriting or operating a keypad.

BACKGROUND TO THE INVENTION

Several hand-exoskeleton devices have been developed that offer limited functionality for simple grasp and release tasks. These hand-exoskeleton devices show little accuracy and have been built for evaluating the clinical significance of hand-exoskeleton device usage in physical therapy. Several studies using robotic hand-exoskeleton devices have been performed outlaying the efficacy of neural rewiring (brain remapping and reorganization) to help stroke patients regain lost fine hand motor skills.

Applicant is not aware of any commercially available, dedicated handwriting assistive and rehabilitative device for stroke survivors. Handwriting rehabilitation is generally conducted by a trained therapist assisting the patient's hand through handwriting tasks to correct finger movements. Simple splint devices and character stencils assist in this process. However therapist fatigue limits the amount of training time that can be achieved.

Alternative handwriting rehabilitation technologies include haptic devices that take advantage of the sense of touch by applying forces, vibrations, or motions to the user which are designed primarily for use in remote surgery and computer gaming applications. One such device is commercially available under the trade name Sensable® Phantom Premium Haptic Device.

These haptic devices have been applied to handwriting rehabilitation. However, studies have shown no clinical evidence that long-term rehabilitation has occurred. The devices are not well suited to handwriting rehabilitation of patients with limited motor skills such as stroke survivors. Existing handwriting haptic devices repeat handwriting sequences on a single-point object (pen or pencil) which does not adequately model the natural handwriting processes that occur in the human hand. International patent publication number WO 95/10396 describes a hand exoskeleton device that is operable to supply a force feedback to a physiological unit for use as an advanced interface device between a human operator and a machine or computer. The device is operable to transmit to the machine information on the configuration of a distal physiological unit of the operator and to supply at least one part of the operator's body with a force feedback sensation. The device employs electric motor actuation via cables and pulleys and provides inextensible flexion only, that is, it only applies force in one direction with the user being required to oppose motion to restore the device to its normal state. The device allows multiple users with similar hand sizes to use the same device without manual adjustment and is well suited to the designed application in haptic feedback devices which provides additional information to the user. The restriction of flexion inhibits fine hand motor movements. The device described is therefore unsuitable for rehabilitation as the assistive force generated will not be sufficient to assist patients with weakened hand muscle strength. With reference to handwriting rehabilitation, the device does not offer the required sensing and actuation precision or high operation speed needed for handwriting tasks.

In contrast, rehabilitation devices need to provide assistance and in some cases perform the bulk of the intended movements.

Patent publication no US20120059291 describes a device that offers independent actuation of individual phalanges through a "push-pull" tendon configuration. This actuation mechanism is not suitable for intricate movement like adjusting the distal interphalangeal or proximal interphalangeal joints without causing some movement to the more proximal joints due to slack or backlash in the actuator. For example, adjusting the distal phalanx position will cause the metacarpophalangeal joint angle and proximal interphalangeal joint angle to change as there is no supporting mechanism other than the bidirectional push-pull cable/tendon. There are also joint angle sensors; sensory feedback is measured at the actuators via changes in cable length or motor positions which is an inaccurate representation of actual finger joint angles.

Since handwriting is such an intricate task, high accuracy in mechanical movements is essential for a successful rehabilitative hand-exoskeleton.

Applicant thus perceives a need for a hand exoskeleton that can assist persons in need of same.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention there is provided a hand exoskeleton device comprising at least three robotic units one of which is for attachment to each of the thumb, index finger, and middle finger of a hand of a user and wherein the robotic unit for attachment to the thumb has at least two elements for attachment to the distal and proximal phalanges of the thumb; and each of the two robotic units for attachment to the index and middle fingers have three elements for attachment to the distal, middle and proximal phalanges of the relevant finger; wherein the elements of each robotic unit are interconnected to a next adjacent element by suitable hardware to provide for relative angular movement of the elements about an axis of rotation that corresponds substantially to the axis of rotation of a relevant patient's interphalangeal joint movement; an actuator associated with the interconnecting hardware of each interconnected pair of elements whereby the angular position of one element relative to the other can be adjusted in each of two opposite directions by operation of the actuator; a sensor associated with the interconnection between each pair of elements for sensing the angular position or force of one element relative to the other element of that pair; and a computerized controller for controlling movement of the elements of each pair by way of the associated actuator according to predetermined input received by the controller from an associated database and on the basis of input received from the sensors.

Further features of the invention provide for each element of each robotic unit to be of arcuate cross-section for engaging the dorsal surface of the relevant finger with attachment means such as a hook and loop (such as that sold under the trade name VELCRO™) fastened strap for firmly attaching each element to its associated phalangeal part of the finger or thumb; for the suitable hardware interconnecting adjacent elements to be a rigid linkage system, conveniently one having a four bar arrangement, such that actuator movement results in angular movement of the phalanges of a finger or thumb substantially about the axis of rotation of the particular joint; for the sensors to be angle sensors such as resistance based sensors in the manner of potentiometers; and for the elements, linkages, and other components to be of light weight with the elements and linkages conveniently being of a suitable plastics material.

The hand-exoskeleton will have thus have at least five actuated finger joints that have the ability in use, to form an actuated tripod-grip of the type that is needed for handwriting rehabilitation. The device of the invention seeks to control and assist the movement of five actuated degrees-of-freedom on the thumb, index and middle fingers that is needed for a tripod handwriting activity.

It is of course within the scope of the invention that additional joints of the hand may be added to those fitted with robotic units as specifically mentioned above. In particular, the interphalageal and metacarpophalangeal joints of the thumb, index and middle fingers may be similarly controlled utilizing additional robotic units with their associated elements. Furthermore, a similar robotic unit could be made for the ring finger as well as the wrist (modeled as a single 2 degrees of freedom unit) may be actuated and sensed. In the instance of the ring finger, the device may support quadropod hand writing grip styles and would most likely be built in the same manner as the robotic units for the middle and index fingers. However, inclusion of wrist may alter the degrees of freedom of the entire system and this needs to be taken into account. The device may in addition, or alternatively, support a cylindrical grasp or a digital grip style.

The device of the invention is thus able to improve traditional handwriting therapy by allowing a patient to perform training exercises at home without the need for a trained therapist. The device assists a patient to complete repetitive handwriting tasks and provides a means to train lost fine hand motor skills while at the recovery phase of rehabilitation.

The general premise is that the device may sense a particular handwriting sequence of movements of the relevant phalangeal joints of the fingers and may therefore be able to repeat the sequence unassisted given enough actuated degrees of freedom and range of movement at each joint location.

In order that the above and other features of the invention may be more fully understood, a more detailed description with particular reference to one embodiment of the invention will now follow with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a general assembly illustration showing a person's hand fitted with a prototype device according to the invention;

Figure 2 is a schematic illustration of the bones of a human hand and wrist for a clear understanding of the application of the invention;

Figure 3 is a three-dimensional view from above of a robotic unit for attachment to either the index or the middle finger;

Figure 4 is a three-dimensional view from beneath and from the opposite side of the robotic unit illustrated in Figure 3;

Figure 5 is a side view of the robotic unit illustrated in Figure 3 from one side thereof;

Figure 6 is a side view of the robotic unit illustrated in Figure 3 from the other side thereof;

Figure 7 is a three-dimensional view from above of a robotic unit for attachment to the thumb of a user; Figure 8 is a three-dimensional view from beneath and from the opposite side of the robotic unit illustrated in Figure 7;

Figure 9 is a side view of the robotic unit illustrated in Figure 7 from one side thereof;

Figure 10 is a side view of the robotic unit illustrated in Figure 7 from the other side thereof;

Figure 1 1 is a three-dimensional view illustrating one type of single element of a robotic unit;

Figure 12 is a three-dimensional illustration of one form of housing for the computerized controller for controlling the robotic units;

Figure 13 is a block diagram illustrating the control circuit of the embodiment of the device described herein; and,

Figure 14 is a plot showing five recorded sensor set-point vectors developed while tracing an equilateral triangle.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the following description one embodiment of hand exoskeleton device according to the invention will be discussed in some detail together with an expanded discussion of the various aspects of the invention.

As illustrated in Figure 1 , the hand exoskeleton device comprises three robotic units (1 , 2, 3) one of which is for attachment to each of the thumb as indicated by numeral (1 ), the index finger as indicated by numeral (2), and the middle finger as indicated by numeral (3), of a hand (4).

The robotic unit (1 ) for attachment to the thumb has two elements (6, 7) for attachment to the distal (106) and proximal phalanges (107) of the thumb (See Figure 2). Each of the two robotic units (2, 3) for attachment to the index and middle fingers have three elements (1 1 , 12, 13) for attachment to the distal (1 1 1 ), middle (1 12) and proximal (1 13) phalanges of the relevant finger.

Each of the elements has the basic form illustrated in Figure 1 1 and has an arcuate bridge portion (14) for bridging the rear surface of the relevant part of the finger or thumb and terminating at each side of the finger or thumb in a pair of lever formations (15) for attachment to another element. In instances in which the element is attached to an actuator, an operating lever formation (16) is provided whereby the angular position of the element can be adjusted relative to an element connected to it by an actuator as described below. Each element has attachment means in the form of a hook and loop fastener strap (17) (such as that sold under the trade name VELCRO™) (see Figure 5) for firmly attaching each element to its associated phalangeal part of the finger. The elements are conveniently made of a suitable plastic material although lightweight metals could also be employed. Of course, only smooth, nonabrasive components should be in contact with skin in order to avoid fatigue or injury. Exposed nerves, blood vessels and tendons must be undisturbed by any mechanical components. In order to develop a high accuracy hand-exoskeleton the elements need to mould to the human hand as snugly as possible.

The elements of each robotic unit are interconnected to a next adjacent element by suitable hardware to provide for relative angular movement of the elements about an axis of rotation that corresponds substantially to the axis of rotation of a relevant patient's interphalangeal joint movements. In this embodiment of the invention the suitable hardware is in the form of a rigid linkage system (21 ), conveniently one having a four bar arrangement, such that movement of individual actuators in the form of miniature dc motors (22) results in angular movement of the phalanges of a finger or thumb substantially about the axis of rotation of the particular joint. The miniature dc motors may be of any suitable type such as servomotors.

Alternatively, other functionally equivalent technologies such as shape memory alloys may also be distantly located from the corresponding elements but connected using alternative force transmission systems such as cables.

The linkage system includes an arm (23) driven by the dc motor and an arcuate link (24) that connects it to the linkage system at one element or between two elements. The arrangement is such that in respect of each pair of elements the actuator associated with the interconnecting hardware can be energized to move the arm (23) angularly in either of the two possible directions to adjust the angular position of one element relative to the other about the centre of rotation of the joint. Of course, this takes place within a predetermined range of movement that is further discussed below. The design of the linkage system targets a compact linkage system that obstructs the user as little as possible during handwriting tasks and that enhances the actuator and sensor precision levels. The linkage system should preferably maintain a substantially linear input-output relationship to simplify controller design. The system should also allow an efficient utilization of shaft power of the dc motors. Individual linkage systems should fit comfortably on the hand-exoskeleton without interfering with adjacent components.

It was experimentally discovered that in multiple lever systems such as this linkage system, a single millimeter change can result in substantial performance improvements. These improvements manifest themselves in linearity curves, joint range of movement and increased achievable workspace.

In order that the angular position of one element relative to the other may be sensed, a sensor (31 ) is associated with each robotic unit for sensing the angular position and/or force of one element relative to an adjacent element of that pair. These sensors are, in this embodiment of the invention, resistance based in the manner of potentiometers.

The dc motors are controlled by a computerized controller (32) for controlling movement of the elements of each pair according to predetermined input received by the controller from an associated database (33) and on the basis of input received from the sensors (31 ). The computerized controller can conveniently be housed in a generally flat housing (34) of the general nature illustrated in Figure 12. The use of a microcontroller suggests that a digital control strategy would be the most suitable since all input and output parameters are already in digital form. Fundamental control system theory places significant emphasis on designing the simplest controller to improve a system response. The hand-exoskeleton described above will have thus have at least five actuated finger joints that have the ability in use, to form an actuated tripod- grip of the type that is needed for handwriting rehabilitation, as will be apparent from the foregoing. As indicated above, the general premise is that the device can sense a particular handwriting sequence of movements of the relevant phalangeal joints of the fingers and should therefore be able to repeat the sequence unassisted given enough actuated degrees-of-freedom and range of movement at each joint location.

It is to be noted that appropriate measures should be taken to combat the possibility of the device causing muscle damage to patients with severe spasticity. This may be addressed by a number of mechanical and electronic safety features. A primary safety feature may be to limit the mechanical strength of critical parts of the device such that a part would physically break in response to excessive force (defined in terms of spasticity). In addition, electronic force sensors may be used to monitor and hence allow for a maximum force limit.

Handwriting pattern recognition and analysis is an extremely broad field. For this reason, closed loop shapes (eg. Circles, triangles and other regular polygons) are used as the handwriting tasks evaluating this embodiment of the invention.

The computerized controller is programmed with data corresponding to the movements of the various fingers of the hand that take place when each of the letters and numerals of the alphabet are to be written or corresponding basic "sub-components" such as a triangle which forms the top part of capital A are to be formed. This may be done empirically by recording the movements of a perfectly healthy hand in order to form the various letters and numerals. An interrelationship between the computerized controller and input from the various sensors is such that the fingers of a user are urged to follow the relevant path to form a particular letter or numeral. Also, the computer can be programmed to recognize what a user is trying to write and assist in the formation of such letter or numeral. By repeating the correct hand movements during a goal-orientated activity, the individual finger joints and muscles are activated in the correct sequence while visual feedback completes the loop effectively performing a neural remapping of fine hand motor skills.

The desired rehabilitative control mode should include multiple handwriting tasks to explore different spatial sequences; the ability to replay sequences at different speeds; and visual representations of the activity goal and actual sequence performed. By replicating the actions performed by a therapist or alternatively, performed by an unaffected hand of the patient such as in the case of stroke, a robotic hand-exoskeleton device can allow the patient to perform handwriting activities more frequently thus improving the overall functional gain in meaningful activities of daily life.

In order to meet proposed rehabilitative control mode, the actuators (dc motors) require closed loop position tracking with zero steady-state error. Additionally the complete system preferably has a fast response time when subjected to external disturbances while maintaining internal system stability. There are various factors that need to be taken into account when constructing a device according to the invention, these including the fact that the elements attached to the various phalanges of the fingers must follow natural movements in order to prevent tissue damage that may be to a muscle, ligament, tendon, bone, vessel or skin. The elements and fastening straps should not disrupt blood circulation in the hand. It is therefore regarded as very important to determine the axis of rotation for individual joints of the hand for each particular patient with care and accuracy although it is envisaged that it may be possible to produce a more generic device according to the size and general characteristics of a patient's hand.

It is important that the arcuate movement of the interconnected elements of the robotic units relative to each other take place substantially about the axis of rotation. In order to allow a natural range of movement of the inter- phalangeal joints the axes of rotation need to be rather accurate. Based on the required accuracy of mechanical components, modeling of the human hand is an important factor in the mechanical design. Actuator and sensor placement need to include a form of "precision amplification" since the components sourced have relatively low output resolutions. One method that was used to model the contours of the human hand involved the tedious process of building a wire framework over the hand and subsequently measuring each wire cross-sectional trace on a 2-D, 1 :1 scale grid.

In this regard, any suitable technique can be employed to determine the centers of rotation and simply to guide the addressee to one possible method of determining the centre of rotation on each side of a joint, and thus the axis of rotation, points on each side of a joint may be measured by taking medial and lateral photos (with a known scale) of a particular interphalangeal joint at different joint angles. These reference points were designed onto the base phalangeal segments to ensure the points measured follow the actual finger trajectory during flexion and extension of a particular interphalangeal joint. This provided a medium to gain data needed for centre of rotation determination. Fixed reference points on the phalanges enabled effective trace loci to be developed having direct relationships to the centre of rotation position. The method of determining the center and ultimately the axis of rotation is an application of simple geometry to solve the engineering problem.

For the purposes of producing a prototype, the joints were photographed at 6 different flexion angles from the medial and lateral aspects while maintaining a parallel plane to the reference markers that is, keeping the plane of the camera parallel to a reference plane on the phalangeal exoskeleton. The resulting 1 2 photos were edited to color-code the rows of the reference grid for image processing. Using custom image processing software, the (x,y) coordinates of the color-coded reference points were extracted and the extracted data rescaled to metric units. The captured data was compared to the original photos for verification.

Handwriting tasks are expected to generate low velocity (i.e. smooth, low magnitude first derivatives) position set-point sequences since the movements are fine, fluid and for the most part, continuous in nature (cursive style handwriting). Only position tracking will be achieved by the control system however the velocity range of the position vectors can affect controller design as nonlinear systems (almost all real systems) respond differently to varying magnitude input steps. The rate at which the position set-point vector changes (i.e. velocity) will identify the range of input step sizes which can reduce the controller specifications.

The term "set-point vector" refers to a vector of sensor readings, recorded (at fixed sampling period, say 5ms) while performing a repetitive handwriting task. The control premise is that if these five set-point vectors are input to the control system, the hand-exoskeleton output will be forced to these values in the correct timing sequence effectively replaying a pre-recorded task. Additionally the angular joint positions are expressed as a digital value such as 10-bit ADC values. The mapping from digital values (integer) to angular degrees (floating-point) is an unnecessary conversion since integer-based mathematics is always favored in microcontroller implementation. However the conversion can be done and displayed/logged for a therapist to review the angular range of motion achieved in metric units (degrees). Figure 14 shows the variation in set-point vectors consequent on triangle handwriting tests in which the graph indicated by numeral (41 ) relates to the distal interphalangeal joint on the middle finger; the graph indicated by numeral (42) relates to the proximal interphalangeal joint on the middle finger; the graph indicated by numeral (43) relates to the distal interphalangeal joint on the index finger; the graph indicated by numeral (44) relates to the proximal interphalangeal joint on the index finger; and the graph indicated by numeral (45) relates to the interphalangeal joint on the thumb. Whilst other forms of controllers may be used, given the design requirements the simplest controller of which applicant is aware and that produces zero steady-state error to constant inputs is a PI controller. This controller is relatively easy to design using the digital Root-Locus design method. After a few modifications a suitable controller was determined with the discrete transfer function given by,

(z - 0.8258\ 0.04547 - 0.0375z^_1

k(z) = 0.04547 - ≡ - with T_s

\ z— 1 / 1— z ¹

= 5ms

Using the direct programming method, the following digital control law was formulated: e [n] = r [n]— y [n]

x[n] = e[n] + x[n— 1]

u[n] = 0.04547 - 0.03755^■ x[n - 1] A device according to the invention can drastically improve the patient's quality of life by promoting self-reliance in activities of daily life such as handwriting and similar fine hand motor skills. Stroke is the leading cause of adult-onset disability resulting in millions of people needing fulltime assistance from caregivers. Traditional stroke upper limb rehabilitation costs are high in therapy fees and can only be performed at rehabilitation clinics reducing effective rehabilitation time. Technology based on the device provided by this invention can provide low-cost rehabilitation options for people in need of physical therapy. The technology can be commercialized into low cost rehabilitation devices that can be used by patients at home thus increasing overall functional progress.

Numerous variations may be made to the embodiment of the invention described above without departing from the scope hereof. As will be quite apparent to those of ordinary skill in the art, numerous different forms of hardware can be used to interconnect the elements of the various robotic units and, in this regard, it is possible that Bowden cables may operate effectively. Also, various forms of sensors can be used as can a variety of different actuators.

Claims

CLAIMS:

1 . A hand exoskeleton device comprising at least three robotic units one of which is for attachment to each of the thumb, index finger, and middle finger of a hand of a user and wherein the robotic unit for attachment to the thumb has at least two elements for attachment to the distal and proximal phalanges of the thumb; and each of the two robotic units for attachment to the index and middle fingers have three elements for attachment to the distal, middle and proximal phalanges of the relevant finger; wherein the elements of each robotic unit are interconnected to a next adjacent element by suitable hardware to provide for relative angular movement of the elements about an axis of rotation that corresponds substantially to the axis of rotation of a relevant patient's interphalangeal joint movement; an actuator associated with the interconnecting hardware of each interconnected pair of elements whereby the angular position of one element relative to the other can be adjusted in each of two opposite directions by operation of the actuator; a sensor associated with the interconnection between each pair of elements for sensing the angular position or force of one element relative to the other element of that pair; and a computerized controller for controlling movement of the elements of each pair by way of the associated actuator according to predetermined input received by the controller from an associated database and on the basis of input received from the sensors.

2. A hand exoskeleton device as claimed in claim 1 in which each element of each robotic unit is of arcuate cross-section for engaging a dorsal surface of a relevant finger or thumb with attachment means in the form of a strap being provided for firmly attaching each element to its associated phalangeal part of the finger or thumb.

3. A hand exoskeleton device as claimed in either one of claims 1 or 2 in which the suitable hardware interconnecting adjacent elements is a rigid linkage system.

4. A hand exoskeleton device as claimed in claim 3 in which the rigid linkage system is one having a four bar arrangement, such that actuator movement results in angular movement of the phalanges of a finger or thumb substantially about the axis of rotation of the particular joint.

5. A hand exoskeleton device as claimed in any one of the preceding claims in which the sensors are angle sensors.

6. A hand exoskeleton device as claimed in any one of the preceding claims in which the sensors are resistance based in the manner of potentiometers.

7. A hand exoskeleton device as claimed in any one of the preceding claims in which the device is configured to have the ability in use, to form an actuated tripod-grip of the type that is needed for handwriting rehabilitation.

8. A hand exoskeleton device as claimed in any one of the preceding claims in which the device seeks to control and assist the movement of five actuated degrees-of-freedom on the thumb, index and middle fingers that is needed for a tripod handwriting activity.

9. A hand exoskeleton device as claimed in any one of the preceding claims in which additional elements may be added to the robotic units for fitment to the interphalageal and metacarpophalangeal joints of the thumb, index and middle fingers.

10. A hand exoskeleton device as claimed in any one of the preceding claims in which one or two additional robotic units are provided for the ring finger as well as the wrist (modeled as a single 2 degrees of freedom unit).

A hand exoskeleton device as claimed in claim 10 in which a robotic unit for the ring finger is configured to support quadropod hand writing grip styles; a cylindrical grasp or a digital grip style.