Actuator with integrated position sensor and play compensation

A method of compensating for play in an actuation system including an actuated system comprising an elastic element, and an actuator with a stepper motor having at least one electrical phase, the method comprising:

• supplying by means of a current controller said at least one electrical phase with a first limited phase current configured to drive the rotor of the stepper motor in a first direction, said limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in said first direction,
• detecting a loss of steps of the stepper motor in said first direction and determining therefrom a first end of mechanical play position,
• driving with a second limited phase current the rotor of the stepper motor in a second direction opposite to the first direction, said second limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in the second direction,
• detecting a loss of steps of the stepper motor in said second direction and determining therefrom a second end of mechanical play position, and
• compensating the actuator for mechanical play in the actuation system based on the first and second ends of mechanical play positions, wherein said detecting a loss of steps is performed by means of a rotor position sensor or by means of a software stall detection algorithm based on current and voltage measurement of an electrical phase of the motor, wherein the loss of steps is detected by sensing a motion direction change on the rotor displacement, and wherein the rotor position sensor comprises a rotary encoder and the motion direction change is detected by quadrature encoder pulse (QEP) signals generated by the rotary encoder.

A method of initializing a position sensor of an actuation system including an actuated system and an actuator with a stepper motor having at least one electrical phase, the method comprising:

• supplying a current to said at least one electrical phase configured to accelerate a rotor of the motor during an acceleration phase,
• switching off the supply current in said at least one electrical phase,
• measuring a back EMF voltage in said at least one electrical phase with the supply current switched off and determining, with the position sensor, a mechanical position of the rotor when the back EMF voltage measurement reaches a pre-defined value, and
• aligning the mechanical position of the rotor with an electrical angle of said at least one electrical phase at said position when the back EMF voltage reaches said pre-defined value.

A method of initializing a position sensor of an actuation system including an actuated system and an actuator with a stepper motor having at least one electrical phase, the method comprising:

• supplying a current to said at least one electrical phase configured to accelerate a rotor of the motor during an acceleration phase,
• switching off the supply current in said at least one electrical phase,
• measuring a back EMF voltage in said at least one electrical phase with the supply current switched off and determining with the position sensor a mechanical position of the rotor when the back EMF voltage measurement reaches a pre-defined value, and
• aligning the mechanical position of the rotor with an electrical angle of said at least one electrical phase at said position when the back EMF voltage reaches said pre-defined value, wherein during said acceleration phase of the rotor, the electrical angle is set one step further than the computed rotor mechanical position in order to produce maximum torque.

An actuator comprising a stepper motor having at least one electrical phase, a controller, a rotor position sensor, and a motion transmission system configured to be coupled to an actuated system,

• wherein the controller is configured to supply said at least one electrical phase with a first limited phase current configured to drive the rotor of the stepper motor in a first direction, said limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in said first direction, and the rotor position sensor is configured to detect a loss of steps of the stepper motor in said first direction and the controller is configured to determine therefrom a first end of mechanical play position,
• and wherein the current controller is configured to supply said at least one electrical phase with a second limited phase current to drive the rotor of the stepper motor in a second direction opposite to the first direction, said second limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in the second direction, said rotor position sensor configured to detect a loss of steps of the stepper motor in said second direction and the controller is configured to determine therefrom a second end of mechanical play position,
• the actuator configured to compensate for mechanical play in the actuated system based on the first and second ends of mechanical play positions.

A method of compensating for play in an actuation system including an actuated system comprising an elastic element, and an actuator with a permanent magnet synchronous (PMS) brushless direct current (BLDC) motor having at least one electrical phase, the method comprising:

• supplying by means of a current controller said at least one electrical phase with a first limited phase current configured to drive in open loop stepper mode the rotor of the BLDC motor in a first direction, said limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in said first direction,
• detecting a loss of steps of the BLDC motor in said first direction and determining therefrom a first end of mechanical play position,
• driving in open loop stepper mode with a second limited phase current the rotor of the stepper motor in a second direction opposite to the first direction, said second limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in the second direction,
• detecting a loss of steps of the BLDC motor in said second direction and determining therefrom a second end of mechanical play position, and
• compensating, by the actuator, for mechanical play in the actuation system based on the first and second ends of mechanical play positions.

An actuator comprising a PMS BLDC motor having at least one electrical phase, a controller, a rotor position sensor, and a motion transmission system configured to be coupled to an actuated system,

• wherein the controller is configured to supply said at least one electrical phase with a first limited phase current configured to drive in open loop stepper mode the rotor of the motor in a first direction, said limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in a normal load operation for actuation of the actuated system in said first direction, and the rotor position sensor is configured to detect a loss of steps of the stepper motor in said first direction and the controller is configured to determine therefrom a first end of mechanical play position,
• and wherein the current controller is configured to supply said at least one electrical phase with a second limited phase current to drive in open loop stepper mode the rotor of the motor in a second direction opposite to the first direction, said second limited phase current having an amplitude inferior to an operational phase current needed to drive the rotor in normal load operation for actuation of the actuated system in the second direction, said rotor position sensor configured to detect a loss of steps of the motor in said second direction and the controller is configured to determine therefrom a second end of mechanical play position,
• the actuator configured to compensate for mechanical play in the actuation system based on the first and second ends of mechanical play positions.