specialfeatures:force_controlabstract

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specialfeatures:force_controlabstract [2017/09/08 15:25] – Pedro Ramilospecialfeatures:force_controlabstract [2024/08/08 13:12] (current) – Removed mention of Direct PWM Marco Prata
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   - Current is typically proportional to torque which in turn can be related to force. However, all forces have to pass through the gearbox of the motor; the gearbox sits between the tendon (output shaft) and the point where current is sampled (before the motor). This poses some particular challenges. The most important is that the current-torque ratio when force travels from the motor to the output shaft is different than the current-torque when the force travels from the output shaft back to the motor. One way to cope with this is to amplify the error value in the control loop, if/when we know the force is traveling from the output shaft back to the motor (which is the direction where some of the force is lost/absorbed by the gearbox).   - Current is typically proportional to torque which in turn can be related to force. However, all forces have to pass through the gearbox of the motor; the gearbox sits between the tendon (output shaft) and the point where current is sampled (before the motor). This poses some particular challenges. The most important is that the current-torque ratio when force travels from the motor to the output shaft is different than the current-torque when the force travels from the output shaft back to the motor. One way to cope with this is to amplify the error value in the control loop, if/when we know the force is traveling from the output shaft back to the motor (which is the direction where some of the force is lost/absorbed by the gearbox).
   - A final consideration should be made about acceleration and settling when reaching the goal position: when the actuator starts a movement or makes corrections near the holding position, there is acceleration which in turn produces a peak in current; this is not necessarily force but instead it is the profile of the beginning of a movement. The control algorithm should take this factor into consideration to avoid reacting to these accelerations.   - A final consideration should be made about acceleration and settling when reaching the goal position: when the actuator starts a movement or makes corrections near the holding position, there is acceleration which in turn produces a peak in current; this is not necessarily force but instead it is the profile of the beginning of a movement. The control algorithm should take this factor into consideration to avoid reacting to these accelerations.
-  - BETA: New firmware for EROS architecture with** Direct PWM Control**. At the time of revising this document (17/Aug/2017), Seed Robotics is working on a new firmware feature that will enable direct control of the PWM applied by the actuators. This means that you will now be able to build an algorithm accessing the variable that directly affects current, instead of controlling position which is an indirect variable. The main advantage is that you are now able to have a much finer control and disable the PID controller of the actuator that would sometimes cause the current to peak as part of its operation and not as result of external force. This results in cleaner current readings and higher precision. This is still in experimental phase but if you would like to give it  a try, please email us at support@seedrobotics.com 
  
  

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  • specialfeatures/force_controlabstract.txt
  • Last modified: 2024/08/08 13:12
  • by Marco Prata