Speed profile and types of motor motion

Speed profile

Overview

The speed profile sets the acceleration, deceleration, and maximum speed values of the motion prior to the motor operation in advance. This depends on the following:

  • Motor Specifications
  • Power supply voltage
  • Load (e.g. on a load cell)
  • Voltage control or current control

You need to set these values according to your actual environment.

Values to be set

The three values, Acceleration(acc),deceleration(dec), and maxSpeed need to be set. You can also set the minimum speed (minSpeed) as a function of the motor driver, but it is fixed at 0 on the firmware because it is unlikely to be used for the actual application.

Setting command

With /setSpeedProfile command you can set above three values. The acc and dec cannot be set unless the motor is stopped, the maxSpeed parameter can be set at anytime.

Type of motor operation

Constant speed

This is the command to drive the the motor with the acceleration/deceleration rate set by the speed profile, then maintains constant speed. It continues to rotate until speed 0 is set, or stop command is sent. The range of speed that can be set is limited to the maximum speed of the speed profile. It will keep BUSY state during the acceleration and deceleration. A representative command for the constant spped drive is /run. There are also /goUntil and /releaseSw commands are available.

Positioning

The trapezoidal drive towards the specified position is performed according to the speed profile. In other words, it accelerates according to the acceleration rate of the speed profile, then drives at constant speed when it reaches the maximum speed, and then decelerates at specified deceleration rate at the timing calculated backwards to stop at the specified position. It may start decelrating before it reaches the maximum speed, especially when you want to accelerate / decelerate relatively slow rate. It remains in the BUSY state until the motor stops. It's not possbile to interrupt the current positioning motion with another positioning motion.

Servo mode

This is not a function of the motor driver, but a mode of driving implemented in the firmware. It constantly updates the constant speed operation to follow a given target position. This mode is similar to tje radio controlled servo motor. No other motor motion commands can be sent while the motor is operating in this mode.

Types of stops

There are two options with a total of four different commands, as follows;

  • Decelerate according to the speed profile or stop instantly.
  • Keep magnetized / excited or goes to the high impedance(High Z) state after stop.
State after stop Deceleration stop Immediate stop
Excitation SoftStop HardStop
HiZ SoftHiZ HardHiZ

The excited state is the state in which the torque is applied to hold the motor position according to KVAL_HOLDvoltage, or current set by the TVAL_HOLD value. The high impedance state is the state where the current is cut off and there is no holding torque.

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