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Lecture 12 Dimitar Stefanov Slide 2 Some more examples of adaptive terminal devices Pneumatic adaptive prosthetic hand Slide 3 Humans manipulate objects by adapting the shape of the hand to that of the target object. They maximize the contact area and so minimize the contact forces required for stable manipulation. The reconfigurable nature of the human hand means the shape it adopts can reflect the task enabling the hand to impart larger forces through a power grip, or finer control using a precision grip. Slide 4 Based on small motors and gearboxes which are placed inside the digital spaces of the artificial hand. Efficient use of space which allowed shorter and small prostheses to be built. Prodigits (powered prosthetic digit system), 1994 Prosthetics Research Group at the Bioengineering Centre in Edinburgh http://www.rehabtech.org.uk/ Slide 5 The Southampton Adaptive Hand Kyberd P.J. and Chappell P.H. The Southampton Hand, An Intelligent Myoelectric Prosthesis. Journal of Rehabilitation Research and Development, 31, 4, pp 326 - 334, 1994. 1 2 3 Basic postures of the hand: Three-point chuck (digits 1,2, and 3) Two-point grip (digits 1 and 2) Fist: As a two-point grip but thumb is fully extended to allow large objects to be grasped Small fist: As fist but with thumb flexed and abducted to oppose side of digit 2 Side (or key): Digits 2 and 3 half flexed with thumb opposing of 2. Flat hand: Digits 2 and 3 fully extended with thumb 1 abducted and flexed. The mechanical hand possesses fingers with separate DOF. the Leverhume Oxford Southampton Hand (LOSH hand) Slide 6 1.A microprocessor processes the information concerning the shape, orientation and stability of the held object within the grasp of a prosthesis. 2.The operator gives simple commands and the controller co-ordinates multiple degrees of freedom to shape the hand to maximize the contact area between the hand and the object and so minimize contact forces. 3.If the object slips this is detected and the controller responds. The Southampton Adaptive Manipulation Scheme (SAMS): Single EMG channel Microprocessor control of the hand (automatic choice of the finger posture, grasping force) Multiple sensors, located on the prosthesis fingers. Slide 7 The Southampton Adaptive Manipulation Scheme (SAMS): Peter Kyberd and Mervyn Evans, Intelligent control of a prosthetic hand, ICORR97, University of Bath. Slide 8 The opening of hand is made proportional to the tension in the commanding muscle channel. When the muscle relaxes the hand closes automatically. If the hand touches an object, sensors in the hand detect this and ensure that only the lightest possible contact force is imparted upon the target. If the object moves the hand closes further to maintain this light touch. If the grip tension is insufficient and the object slips this is detected and the hand responds automatically. The hand posture is depending where the hand touches first. Slide 9 Mechanical details Oxford Orthopaedic Engineering Centre, Nuffield Orthopaedic Centre, Headington, Oxford, UK http://www.tagish.co.uk/losh/images.htm Slide 10 Myoelectric controlled UEP commercialized in the 1960s Six Million-Dollar 1960's-era experimental arm. By the mid 80s, the use of myoelectric hands had slowly grown to an estimated 10% of upper limb amputees in the United States Today, over 50% of new amputees in the U.S. and in Europe are now fitted for a myoelectric device, although many arm amputees may still receive both an electric and a body-powered prosthesis. The motor-driven hand provides a higher level of pinch force, up to five times greater than a body-powered hand, without requiring more effort by the wearer. First introduced in the early 1960s Slide 11 Comfort A myoelectric prosthesis, by eliminating the need for control cables, reduces the restriction to body movement and the discomfort of the control cable. Natural posture of the user during the elaboration of the commands for prosthesis activation. The latest generation of myoelectric devices also can be adjusted to operate at a very low level of muscle contraction, so that the wearer is less fatigued than with earlier systems. Cases when a patient may not be able to use myoelectric control: lack of muscle strength after nerve damage, extensive and fragile scar tissue over muscle sites, tendency for the socket to shift on the wearer's body and move the electrodes (patients who have the tendency to gain or lose weight frequently). Slide 12 Function In the electric hand, the pinch force can be controlled up to 22 pounds (10 kg.). Cosmesis Electric hands can look quite natural. Convenience fast battery chargers that charge in about two hours; improved battery packs which give up to twice the life as earlier versions; improved electric motors with higher power-to-weigh ratio; long life motors. Cost still significantly greater than body powered arms. In many countries reimbursement of a part of the price What should be done further? - Lighter weight hands with good reliability and water resistant components; lower cost prostheses. Gloves for electric hands are still too easily stained. Slide 13 Electric elbows: First introduced in the late 1960s. Now - the "second generation" of these devices. Proportional control and automatic elbow lock, i.e., no cable must be pulled to lock the elbow. The elbow could be switch or servo operated. Still high price of the sophisticated constructions, so there is a market mainly for elbow joints with switch control allowing one speed of operation. Problem The lightweight elbow can be designed if the lifting speed is limited. The electric hand adds a weight concentration at the end of the forearm. The Utah Arm 2 Electric Elbow Slide 14 Myoelectric Hand Orthosis Rehabilitation Engineering R&D Lab, VA Medical Center, W. Roxhury, Massachusetts 02132. For the spinal cord injury patients at the C5-6 level Weigh - 500 grams Proportionally operated A major function of the hand orthosis (HO) is to provide the ability to pinch, grip, and release objects during daily living activities. The ideal HO uses the skeletal structure and the biomechanical properties of the users limb as an integral part of its powered mechanical system. Slide 15 http://www.oandp.org/jpo/22/22149.asp