Difference between revisions of "Control modes"

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(→‎Torque control)
(→‎Velocity control)
 
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==Torque control==
 
==Torque control==
 
[[File:Force-torque-wrench.jpg|thumb|140px|Torque]]
 
[[File:Force-torque-wrench.jpg|thumb|140px|Torque]]
−
Torque control mode makes motor a torque or force transducer. I.e. user sets torque reference to 1 Nm, then motor will produce 1 Nm torque regardless of spinning speed. In torque mode user can not set limits to velocity or position.
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Torque control mode makes motor a torque or force transducer. I.e. user sets torque setpoint to 1 Nm, then motor will produce 1 Nm torque regardless of spinning speed. In torque mode user can not set limits to velocity or position.
  
 
;Typical applications  
 
;Typical applications  
−
*Feeding/pulling
+
*Feeding/pulling/winding
 
*Racing/flight simulators
 
*Racing/flight simulators
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*Final stage in velocity or position controller
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*The final stage in velocity or position controller (see below)
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*Non-motion applications: high power adjustable current source
+
  
 
==Velocity control==
 
==Velocity control==
 
[[File:Turning.jpg|thumb|140px|Velocity]]
 
[[File:Turning.jpg|thumb|140px|Velocity]]
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Goal of velocity control is to regulate motor speed. I.e. if user velocity reference is 500 rpm, then motor attempts to rotate exactly at 500 rpm no matter how much load is attached to motor. In velocity mode user can set limits for torque but not for position.
+
Goal of velocity control is to regulate motor speed. I.e. if user velocity setpoint is 500 rpm, then motor attempts to rotate exactly at 500 rpm no matter how much load is attached to motor. In velocity mode user can set limits for torque but not for position.
  
 
;Typical applications  
 
;Typical applications  
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*Fans & pumps
 
*Fans & pumps
 
*Screw tightening robot when used with torque limit
 
*Screw tightening robot when used with torque limit
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*Intermediate stage in position control
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*The intermediate stage in position control (see below)
  
 
==Position control==
 
==Position control==
 
[[File:CartesianRobot.gif|thumb|140px|Position]]
 
[[File:CartesianRobot.gif|thumb|140px|Position]]
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Position control mode attempts to provide precision positioning. Motor follows reference set point and if set point is kept constant, motor holds position even if external forces attempt to displace it. In position mode user can set limits to torque and velocity.
+
Position control mode attempts to provide precision positioning. Motor follows setpoint set point and if set point is kept constant, motor holds position even if external forces attempt to displace it. In position mode user can set limits to torque and velocity.
  
 
;Typical applications  
 
;Typical applications  
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==Controller structure==
 
==Controller structure==
 
[[File:Cascade position controller.png|thumb|500px|Simplified VSD drive block diagram in position mode. Limiters are not pictured. ]]
 
[[File:Cascade position controller.png|thumb|500px|Simplified VSD drive block diagram in position mode. Limiters are not pictured. ]]
−
VSD drives use cascaded controllers. So for example in velocity mode, torque controller and velocity contoller are connected in series so that torque reference is generated by velocity controller. Position mode is same as velocity controller except the velocity reference is generated by position controller.
+
VSD drives use cascaded controllers. So for example in velocity mode, torque controller and velocity contoller are connected in series so that torque setpoint is generated by velocity controller. Position mode is same as velocity controller except the velocity setpoint is generated by position controller.
  
 
Cascaded structure leads to more flexible features and enables higher dymamic performance compared to direct PWM or torque control from position controller.
 
Cascaded structure leads to more flexible features and enables higher dymamic performance compared to direct PWM or torque control from position controller.
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:User torque rererence → Torque limiter → Torque controller outputs motor PWM
 
:User torque rererence → Torque limiter → Torque controller outputs motor PWM
 
;Velocity controller stucture
 
;Velocity controller stucture
−
:User velocity reference → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM
+
:User velocity setpoint → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM
 
;Position controller stucture
 
;Position controller stucture
−
:User position reference → Position controller outputs velocity reference → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM
+
:User position setpoint → Position controller outputs velocity setpoint → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM
  
−
Limiters simply cut and saturate reference signal if user specified torque/velocity limit is exceeded.
+
Limiters simply cut and saturate setpoint signal if user specified torque/velocity limit is exceeded.

Latest revision as of 21:26, 3 September 2013

There are three main control modes in motion & motor control are torque, velocity and position control.

Torque control[edit | edit source]

Torque

Torque control mode makes motor a torque or force transducer. I.e. user sets torque setpoint to 1 Nm, then motor will produce 1 Nm torque regardless of spinning speed. In torque mode user can not set limits to velocity or position.

Typical applications
  • Feeding/pulling/winding
  • Racing/flight simulators
  • The final stage in velocity or position controller (see below)

Velocity control[edit | edit source]

Velocity

Goal of velocity control is to regulate motor speed. I.e. if user velocity setpoint is 500 rpm, then motor attempts to rotate exactly at 500 rpm no matter how much load is attached to motor. In velocity mode user can set limits for torque but not for position.

Typical applications
  • Spindles
  • Feeding
  • Fans & pumps
  • Screw tightening robot when used with torque limit
  • The intermediate stage in position control (see below)

Position control[edit | edit source]

Position

Position control mode attempts to provide precision positioning. Motor follows setpoint set point and if set point is kept constant, motor holds position even if external forces attempt to displace it. In position mode user can set limits to torque and velocity.

Typical applications
  • CNC
  • Pick & place machines
  • 2D/3D printing
  • Robotics
  • Welding

Controller structure[edit | edit source]

Simplified VSD drive block diagram in position mode. Limiters are not pictured.

VSD drives use cascaded controllers. So for example in velocity mode, torque controller and velocity contoller are connected in series so that torque setpoint is generated by velocity controller. Position mode is same as velocity controller except the velocity setpoint is generated by position controller.

Cascaded structure leads to more flexible features and enables higher dymamic performance compared to direct PWM or torque control from position controller.

Torque controller stucture
User torque rererence → Torque limiter → Torque controller outputs motor PWM
Velocity controller stucture
User velocity setpoint → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM
Position controller stucture
User position setpoint → Position controller outputs velocity setpoint → Velocity limiter → Velocity controller outputs torque rererence → Torque limiter → Torque controller outputs motor PWM

Limiters simply cut and saturate setpoint signal if user specified torque/velocity limit is exceeded.

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