Patent ID: 8516913

Claim:
An actuator ( 10 ) comprising: a first drive pulley ( 28 ); a second drive pulley ( 29 ), the first drive pulley and the second drive pulley being interconnected to rotate together; a first driven pulley ( 52 ; 70 ); a second driven pulley ( 53 ; 72 ); a first guide pulley ( 48 ); a second guide pulley ( 49 ); an endless drive belt ( 40 ) engaging the first and second drive pulleys, the first and second driven pulleys and the first and second guide pulleys; a motor ( 19 ) connected to drive the first and second drive pulleys to rotate and drive the endless drive belt; a driven member ( 50 ; 88 ; 71 , 73 ) carrying at least one of the driven pulleys; the first and second drive pulleys being arranged so that upon rotation thereof the circumferential speed of the first drive pulley is different from the circumferential speed of the second drive pulley, the endless drive belt being looped around the drive pulleys, the driven pulleys and the guide pulleys so that the difference between the circumferential speed of the first drive pulley and the circumferential speed of the second drive pulley causes movement of the driven member; wherein each of the drive pulleys, driven pulleys and guide pulleys having a respective axis of rotation, two of the pulleys being angled pulleys, the axis of rotation of the angled pulleys being angled relative to the axis of rotation of the other pulleys whereby the drive belt undergoes twisting movement on the path between the angled pulley and an adjacent pulley.