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External powered prostheses
External Powered Prostheses--D. C. Simpson
EXTERNAL
POWERED
PROSTHESES
D. C,. SIMPSON, Edinburgh EXTERNAL POWER
External power is normally only used in a prosthesis when there is no convenient source of body-power. Electricity and Carbon Dioxide gas under pressure are the only two types of energy used clinically, and the choice between them is largely decided by the number of actuators required. If only one is needed, electricity gives the lightest system--if more than two are required gas is by far the lightest. In practice the difficulty is not how to power the prosthesis but how to control the power. CHOICE OF CONTROL SYSTEM
With the high above elbow bilateral or amelic congenital amputee there is a shortage of body control sites so the available sites must be employed as economically as possible. The control sites can be employed to control separate anatomical joints of an artificial arm, or the different variables, such as rate and range, of a series of programmed movements, or they can be employed to control linked movements which correspond directly to changes in the spatial position of the hand. In Edinburgh we have elected to control on the latter basis. The variables we have chosen are the distance of the hand from the shoulder, the angles of elevation and of azimuth of the hand with respect to the shoulder, and the rotation of the hand about a horizontal axis. These movements correspond approximately to movements of reaching out, of up and down, and of left and right, the hand rotation corresponding approximately to the pronation/supination movement. In addition to this we have arranged the mechanism so that the hand remains level, or at any preset angle, throughout all movements it executes so that it can be adjusted to be at the most suitable angle for prehension from horizontal surfaces. POSITION CONTROL
Having secured an economical system for control sites the next problem lies in the control itself. If the action of the prosthesis has to be monitored visually then its control is extremely difficult because the movement which occurs in the hand may be compounded of components from each one of the controls. To avoid this complication we have therefore employed a servo control system where the position of the hand in every one of its separate movements is determined by the position of the shoulder or control site. Because we employ the shoulder as a source of control sites the physiological angle receptors in the joint can pass information to the central nervous system about its position, and therefore the hand position, and thus allow unconscious control of the artificial arm. In effect they act as if they were natural receptors incorporated in the artificial arm. This paper gives a short description of the points made in a film shown at the symposium.
Vol. 3
No. 2
1971
213
The Hand
September 1971
This portrait is reproduced by permission of the Trustees of the National Portrait Gallery. Photographer Walter Bird AIR VICE-MARSHAL GEORGE H. MORLEY, CB, CBE, QHS, FRCS
214
Vol. 3
No. 2
1971
The Hand
September 1971
George Morley died suddenly from a heart attack on 26th May 1971. He was b o r n on 22rid F e b r u a r y 1907 in Portsmouth, the son of Doctor G. F. Morley. He preserved and used some of his father's instruments, he valued the craftmanship of their manufacture as he did of old furniture and fine machinery. He personally sharpened and re-set his blades, he tuned his car and planted his own garden. He was widely read in history and English literature and could recall and quote m u c h of it. He had, sometimes to the dismay of his students, an intimate knowledge of anatomy and based his surgery on sound fact. He was firstly a doctor and a family man. He married Jane in 1944 and is survived by her, their daughter Georgina and son John, an engineer. He believed in people and their personal problems. He was a staunch supporter of the Church and the Monarchy, his administrative precision was faultless and in Committees, by careful preparation and subtle interpolation, he steered discussions to achieve the best results. He qualified from the Middlesex Hospital in 1929 and joined the Royal Air Force in 1934. In 1940 he worked at East Grinstead with the late Sir Archibald McIndoe. A Plastic Surgery U n i t was established at Halton under Wing C o m m a n d e r David Matthews with Sir Archibald as Civilian Consultant. The war time commitment closed down in 1947. In 1953 a new centre was opened with George Morley in charge supported by W.O. Baird, Senior Consultant in Dental Surgery, for the treatment of Plastic, Facio-maxillary, and H a n d Surgery and Burns. Morley's experience of Dupuytren's contracture and of free tendon grafting was enormous. Papers were read and published from his hand on The First Aid and Early Treatment of Burns (including Aircrew burns), Flexor tendon injuries, and many other subjects. In 1961 he was appointed President of the British Association of Plastic Surgeons and in 1962 gave the first McIndoe Memorial lecture. In 1965 he gave the Ruscoe Clarke Memorial lecture at Birmingham. As Honorary Secretary of the " H a n d Club" he was prominent in the negotiations between it and the "Second H a n d Club" leading eventually to the formation of "the present British Society for Surgery of the Hand. H a n d Surgery has been his prominent interest. He devised a splint for elevation of the arm post-operatively which has been used continuously at Halton since. His surgery was meticulous, based on functional reconstruction emphasising sensation as well as movement. He worked for the joy of it. His Queen and his country bestowed honours on h i m and he loved them, but be worked beyond his own capacity because of his Art. J, S.W.
Vol. 3
No. 2
1971
215
EXTERNAL
POWERED
PROSTHESES
D. C,. SIMPSON, Edinburgh EXTERNAL POWER
External power is normally only used in a prosthesis when there is no convenient source of body-power. Electricity and Carbon Dioxide gas under pressure are the only two types of energy used clinically, and the choice between them is largely decided by the number of actuators required. If only one is needed, electricity gives the lightest system--if more than two are required gas is by far the lightest. In practice the difficulty is not how to power the prosthesis but how to control the power. CHOICE OF CONTROL SYSTEM
With the high above elbow bilateral or amelic congenital amputee there is a shortage of body control sites so the available sites must be employed as economically as possible. The control sites can be employed to control separate anatomical joints of an artificial arm, or the different variables, such as rate and range, of a series of programmed movements, or they can be employed to control linked movements which correspond directly to changes in the spatial position of the hand. In Edinburgh we have elected to control on the latter basis. The variables we have chosen are the distance of the hand from the shoulder, the angles of elevation and of azimuth of the hand with respect to the shoulder, and the rotation of the hand about a horizontal axis. These movements correspond approximately to movements of reaching out, of up and down, and of left and right, the hand rotation corresponding approximately to the pronation/supination movement. In addition to this we have arranged the mechanism so that the hand remains level, or at any preset angle, throughout all movements it executes so that it can be adjusted to be at the most suitable angle for prehension from horizontal surfaces. POSITION CONTROL
Having secured an economical system for control sites the next problem lies in the control itself. If the action of the prosthesis has to be monitored visually then its control is extremely difficult because the movement which occurs in the hand may be compounded of components from each one of the controls. To avoid this complication we have therefore employed a servo control system where the position of the hand in every one of its separate movements is determined by the position of the shoulder or control site. Because we employ the shoulder as a source of control sites the physiological angle receptors in the joint can pass information to the central nervous system about its position, and therefore the hand position, and thus allow unconscious control of the artificial arm. In effect they act as if they were natural receptors incorporated in the artificial arm. This paper gives a short description of the points made in a film shown at the symposium.
Vol. 3
No. 2
1971
213
The Hand
September 1971
This portrait is reproduced by permission of the Trustees of the National Portrait Gallery. Photographer Walter Bird AIR VICE-MARSHAL GEORGE H. MORLEY, CB, CBE, QHS, FRCS
214
Vol. 3
No. 2
1971
The Hand
September 1971
George Morley died suddenly from a heart attack on 26th May 1971. He was b o r n on 22rid F e b r u a r y 1907 in Portsmouth, the son of Doctor G. F. Morley. He preserved and used some of his father's instruments, he valued the craftmanship of their manufacture as he did of old furniture and fine machinery. He personally sharpened and re-set his blades, he tuned his car and planted his own garden. He was widely read in history and English literature and could recall and quote m u c h of it. He had, sometimes to the dismay of his students, an intimate knowledge of anatomy and based his surgery on sound fact. He was firstly a doctor and a family man. He married Jane in 1944 and is survived by her, their daughter Georgina and son John, an engineer. He believed in people and their personal problems. He was a staunch supporter of the Church and the Monarchy, his administrative precision was faultless and in Committees, by careful preparation and subtle interpolation, he steered discussions to achieve the best results. He qualified from the Middlesex Hospital in 1929 and joined the Royal Air Force in 1934. In 1940 he worked at East Grinstead with the late Sir Archibald McIndoe. A Plastic Surgery U n i t was established at Halton under Wing C o m m a n d e r David Matthews with Sir Archibald as Civilian Consultant. The war time commitment closed down in 1947. In 1953 a new centre was opened with George Morley in charge supported by W.O. Baird, Senior Consultant in Dental Surgery, for the treatment of Plastic, Facio-maxillary, and H a n d Surgery and Burns. Morley's experience of Dupuytren's contracture and of free tendon grafting was enormous. Papers were read and published from his hand on The First Aid and Early Treatment of Burns (including Aircrew burns), Flexor tendon injuries, and many other subjects. In 1961 he was appointed President of the British Association of Plastic Surgeons and in 1962 gave the first McIndoe Memorial lecture. In 1965 he gave the Ruscoe Clarke Memorial lecture at Birmingham. As Honorary Secretary of the " H a n d Club" he was prominent in the negotiations between it and the "Second H a n d Club" leading eventually to the formation of "the present British Society for Surgery of the Hand. H a n d Surgery has been his prominent interest. He devised a splint for elevation of the arm post-operatively which has been used continuously at Halton since. His surgery was meticulous, based on functional reconstruction emphasising sensation as well as movement. He worked for the joy of it. His Queen and his country bestowed honours on h i m and he loved them, but be worked beyond his own capacity because of his Art. J, S.W.
Vol. 3
No. 2
1971
215