Power controller for linear actuator in docking device
A power controller of a linear actuator 10 in a docking device 1 including a six-axis parallel link mechanism 5 , wherein a motor driver 11 configured to control rotation speed of a motor M of the linear actuator 10 on the basis of a load produced on the link 4 includes a speed controlling unit 31 that outputs a current command, a current controlling unit 32 that converts the current command to a voltage command, and a current command limiter 33 that limits the current command of the speed controlling unit 31 so that power consumption per one linear actuator 10 is one sixth or less of the power supply capacity for the motor power, thus allowing for mounting the docking device 1 even for a spacecraft with a small power supply capacity, without requiring modification of the power supply capacity.
1 . A power controller of a linear actuator in a docking device, the docking device comprising a six-axis parallel link mechanism whose component is six links driven to extend and contract by the linear actuator,
the power controller controlling power to be supplied to the linear actuator of each link,
the power controller comprising a motor driver configured to control rotation speed of a motor serving as a drive source of the linear actuator on the basis of a load produced in an axial direction of the link at the time of docking,
the motor driver comprising a speed controlling unit configured to output a current command to the motor based on a speed command of the motor, a current controlling unit configured to convert the current command from the speed controlling unit to a voltage command, and a current command limiter between the speed controlling unit and the current controlling unit,
wherein the current command limiter limits the current command so that power consumption per one linear actuator is one sixth or less of the power supply capacity for the motor power,
wherein the current command limiter has a table of a limit value of a current with respect to the rotation speed of the motor, and changes the limit value of the current between a power running region that rotationally drives the motor and a regeneration region in which the motor rotates by external load, and
wherein, when a limit value aiming for protecting the motor and the motor driver or a limit value aiming for load limitation is greater than a limit value calculated from the table when the rotation speed of the motor is 0, the current command limiter extends a limit curve of the power running region to the regeneration region in an opposite direction to a power running movement, to set the limit value of the current.
2 . The power controller of the linear actuator in the docking device according to claim 1 , wherein the motor driver comprises an anti-windup controller configured to prevent output saturation in the speed controlling unit.
3 . The power controller of the linear actuator in the docking device according to claim 2 , wherein the current command limiter calculates a current i at the time of power running of the motor by the following formula:
i={−ω×kt +√(ω× kt ){circumflex over ( )}2+4× R×Pd )}/(2× R )
wherein ω is the rotation speed of the motor, kt is a torque constant of the motor, R is a sum of a motor resistance and a driver resistance, and Pd is an input voltage of one driver at the time of power running of the motor.
4 . The power controller of the linear actuator in the docking device according to claim 1 , wherein the current command limiter calculates a current i at the time of power running of the motor by the following formula:
i={−ω×kt +√(ω× kt ){circumflex over ( )}2+4× R×Pd )}/(2× R )
wherein ω is the rotation speed of the motor, kt is a torque constant of the motor, R is a sum of a motor resistance and a driver resistance, and Pd is an input voltage of one driver at the time of power running of the motor.