Actuator

Abstract

This invention relates to an actuator and has particular reference to linear and rotary actuators, particularly those for use in the control of robotic arms. The invention provides a relatively low cost means of achieving substantially backlashfree rotary and/or linear motion. There is provided 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 ); an endless drive belt ( 40 ) engaging the first and second drive pulleys and the first and second driven 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 and the driven 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.

1 . 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 );    an endless drive belt ( 40 ) engaging the first and second drive pulleys and the first and second driven 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 and the driven 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.    
   
   
       2 . An actuator according to  claim 1  in which the first and second drive pulleys are arranged so that upon rotation thereof the circumferential speeds differ because of: 
 {i} the first drive pulley having a different circumferential length than the second drive pulley;    {ii} the first drive pulley having a different rate of rotation to the second drive pulley;    {iii} the first drive pulley having a different circumferential length than the second drive pulley and a different rate of rotation to the second drive pulley.    
   
   
       3 . An actuator according to  claim 1  in which there are two driven members ( 71 ,  73 ), the driven members being interconnected together by a second drive belt ( 74 ), the second drive belt engaging a pulley ( 81 ) mounted for rotary movement.  
   
   
       4 . An actuator according to  claim 1  in which the driven member is a carriage ( 50 ;  88 ) mounted for linear movement.  
   
   
       5 . An actuator according to  claim 4  in which the first driven pulley and the second driven pulley are both mounted upon the carriage ( 50 ;  88 ), the actuator further including: 
 a first guide pulley ( 48 ) and    a second guide pulley ( 49 )    the endless drive belt also engaging the first guide pulley and the second guide pulley.    
   
   
       6 . An actuator according to  claim 5  in which the driven pulleys ( 52 ,  53 ) are located between the drive pulleys ( 28 ,  29 ) and the guide pulleys ( 48 ,  49 ).  
   
   
       7 . An actuator according to  claim 6  in which the endless drive belt passes from the first drive pulley ( 28 ) to the first driven pulley ( 52 ), from the first driven pulley to the second drive pulley ( 29 ), from the second drive pulley to the first guide pulley ( 48 ), from the first guide pulley to the second driven pulley ( 53 ), from the second driven pulley to the second guide pulley ( 49 ), and from the second guide pulley back to the first drive pulley, the endless drive belt defining a first loop between the first driven pulley and the drive pulleys, and a second loop between the second driven pulley and the guide pulleys, rotation of the drive pulleys in a first direction causing an increase in the length of the first loop and a corresponding decrease in the length of the second loop.  
   
   
       8 . An actuator according to  claim 6  having a third driven pulley ( 84 ) and a fourth driven pulley ( 85 ), the drive pulleys ( 28 ,  29 ) and all four of the driven pulleys ( 52 ,  53 ,  84 ,  85 ) being mounted upon the driven member ( 88 ), in which the endless drive belt passes from the first drive pulley ( 28 ) to the first driven pulley ( 52 ), from the first driven pulley to the first guide pulley ( 48 ), from the first guide pulley to the third driven pulley ( 84 ), from the third driven pulley to the second drive pulley ( 29 ), from the second drive pulley to the fourth driven pulley ( 85 ), from the fourth driven pulley to the second guide pulley ( 49 ), from the second guide pulley to the second driven pulley ( 53 ), and from the second driven pulley back to the first drive pulley, the endless drive belt defining a first loop between the first guide pulley and the first and third driven pulleys, and a second loop between the second guide pulley and the second and fourth driven pulleys, rotation of the drive pulleys in a first direction causing an increase in the length of the first loop and a corresponding decrease in the length of the second loop.  
   
   
       9 . An actuator according to  claim 1  having two driven members ( 71 ,  73 ), each driven member mounting a respective driven pulley ( 70 ,  72 ), in which the endless drive belt passes from the first drive pulley ( 28 ) to the first driven pulley ( 70 ), from the first driven pulley to the second drive pulley ( 29 ), from the second drive pulley to the second driven pulley ( 72 ), and from the second driven pulley back to the first drive pulley, the endless drive belt defining a first loop between the first driven pulley and the drive pulleys, and a second loop between the second driven pulley and the drive pulleys, rotation of the drive pulleys in a first direction causing an increase in the length of the first loop and a corresponding decrease in the length of the second loop.  
   
   
       10 . An actuator according to  claim 1  having two driven members ( 71 ,  73 ), each driven member mounting a respective driven pulley ( 70 ,  72 ), a first guide pulley ( 48 ) and a second guide pulley ( 49 ), in which the endless drive belt passes from the first drive pulley ( 28 ) to the first guide pulley ( 48 ), from the first guide pulley to the first driven pulley ( 70 ), from the first driven pulley to the second drive pulley ( 29 ), from the second drive pulley to the second driven pulley ( 72 ), from the second driven pulley to the second guide pulley ( 49 ), and from the second guide pulley back to the first drive pulley, the endless drive belt defining a first loop between the first driven pulley and the second drive and first guide pulleys, and a second loop between the second driven pulley and the second drive and second guide pulleys, rotation of the drive pulleys in a first direction causing an increase in the length of the first loop and a corresponding decrease in the length of the second loop.  
   
   
       11 . An actuator according to  claim 1  in which a control line ( 55 ;  55   a ,  55   b ) is connected to the driven member, movement of the driven member causing corresponding movement of the control line.  
   
   
       12 . An actuator according to  claim 1  in which the first drive pulley ( 28 ) and the second drive pulley ( 29 ) are interconnected to rotate in opposite directions.  
   
   
       13 . An actuator according to  claim 1  in which the first drive pulley and the second drive pulley each have an axis of rotation, the axis of rotation of the first drive pulley being parallel to the axis of rotation of the second drive pulley, and in which the first driven pulley and the second driven pulley also each have an axis of rotation, the axis of rotation of the first driven pulley, and the axis of rotation of the second driven pulley, being non-parallel with the axis of rotation of the first drive pulley and the axis of rotation of the second drive pulley.  
   
   
       14 . An actuator according to  claim 13  in which the drive pulleys and the driven pulleys are arranged so that the drive belt undergoes twisting movement on the path between these pulleys, but undergoes substantially no lateral movement.