Minimization of torque ripple

Abstract

Systems and methods of operating an electric motor including a first linear actuator including a first coil, a second linear actuator including a second coil, a rotational shaft, a cam assembly mounted on said rotational shaft for translating linear movement of the first and second linear actuators to rotational movement of the rotational shaft. The first coil is driven with a first signal that produces a first radially-directed force. The second coil is simultaneously driven with a second signal that produces a second radially-directed force, wherein the first radially-directed force is represented by a sine function and the second radially-directed force is represented by the sine function phase shifted by ±π/2 radians.

1 . A method of operating an electric motor including a first linear actuator including a first coil, a second linear actuator including a second coil, a rotational shaft, a cam assembly mounted on said rotational shaft for translating linear movement of the first and second linear actuators to rotational movement of the rotational shaft, said method comprising:
 driving the first coil with a first drive signal that produces a first torque on the rotational shaft;   simultaneously driving the second coil with a second drive signal that produces a second torque on the rotational shaft,   wherein the sum of the first torque and the second torque produces a total torque, and   wherein the first drive signal and the second drive signal are selected to result in the total torque being substantially ripple free throughout a complete rotation of the rotational shaft.   
     
     
         2 . The method of  claim 1 , wherein the first drive signal varies periodically over a complete rotation of the rotational shaft and the second drive signal varies periodically over the complete rotation of the rotational shaft. 
     
     
         3 . The method of  claim 2 , wherein the first drive signal and the second drive signal each have a period of n cycles per a complete rotation of the rotational shaft, wherein n is an even integer. 
     
     
         4 . The method of  claim 3 , wherein n equals 4. 
     
     
         5 . The method of  claim 1 , wherein the first drive signal is shifted in phase relative to the second drive signal by ± 
       
         
           
             
               π 
               
                 2 
                  
                 n 
               
             
           
         
       
       radians, wherein n is an integer. 
     
     
         6 . The method of  claim 1 , wherein the cam assembly presents to the first linear actuator a first cam surface having a first profile and presents to the second linear actuator a second cam surface having a second profile, wherein a first derivative of the first profile is represented by Ψ(n c ·θ) and a first derivative of the second profile is represented by Ψ(n c ·θ+Δ), wherein θ is an angle of rotation of the rotational shaft, n, is an even integer representing a number of cycles of the first profile the and second profile over a complete rotation of the rotational shaft, and Δ is a phase shift between the first profile and the second profile,
 wherein the first drive signal causes the first linear actuator to generate a force represented by F c (n c ·θ) and the second drive signal causes the second linear actuator to generate a force represented by F c (n c ·θ+Δ), and 
 wherein the first drive signal and the second drive signal are selected to cause F c (n c ·θ)·Ψ(n c ·θ)+F c (n c ·θ+Δ)·Ψ(n c ·θ+Δ) to be constant as a function of θ. 
 
     
     
         7 . The method of  claim 1 , wherein the cam assembly presents to the first linear actuator a first cam surface having a first profile and presents to the second linear actuator a second cam surface having a second profile, wherein the first profile, the second profile, the first drive signal and the second drive signal are selected to result in the total torque being substantially ripple free throughout the complete rotation of the rotational shaft. 
     
     
         8 . The method of  claim 7 , wherein the first profile is described by n cycles of a trigonometric function, wherein n is an even integer. 
     
     
         9 . The method of  claim 8 , wherein the second profile is described by n cycles of said trigonometric function. 
     
     
         10 . The method of  claim 9 , wherein n equals 4. 
     
     
         11 . The method of  claim 9 , wherein said trigonometric function is a sine function.