Pioneer 2 / PeopleBot manual Pioneer in Motion, PID Controls

ActivMedia Robotics

and velocity of the robot.

When in translation/ rotation (TR) motion control (recommended), separate translation and rotation servers work independently to achieve the specified forward/ reverse speed and heading of the robot. P2OS will try to make the robot achieve the desired translational velocity and rotate to the desired heading as soon as the commands are received. Acceleration and deceleration managers, which default values you may prepare and also change on-the-fly (SETRA and SETA), operate independently for translation and rotation, too.

Pioneer in Motion

When P2OS receives a translation, rotation, or direct-wheel velocity command, it accelerates the robot at the SETA (both TR and VEL2 modes)and SETRA (TR mode only) rates you program, or at the rates preset in the P2OS configuration parameters. Rotational headings and translational setpoints are achieved by a trapezoidal velocity function. This function is recomputed each time a new motion command is received, making on-the-fly changes possible.

Rotational and translational velocities are limited to the maximum values set in the P2OS parameters or which you may reset with the SETVEL and

SETRV commands. Maximums take affect

on subsequent

commands, not previously established velocity or heading setpoints.

max velocity	short turn,
	max velocity
rotational	not reached
velocity
accel	decel
time
start	position	position
position	achieved	achieved

Figure 20. Pioneer’s trapezoidal turning velocity profile

Note that with P2OS version 1.8 and later, you may override deceleration with the emergency stop (E_STOP) command number 55 or with the Emergency STOP button enabled on the Performance PeopleBot (E_STALL command #56). Accordingly, the robot brakes to zero translational and rotational velocities with very high deceleration and remains stopped until it receives a subsequent translational or rotational velocity command from the client. (See E_STOP and E_STALL later in this chapter.)

PID Controls

The Pioneer drive servers use a common Proportional-Integral-Derivative (PID) control system to adjust the PWM pulse width at the drivers and subsequent power to the motors. The motor-duty cycle is 200 µsec; pulse-width is proportional 0-500.

The P2OS drive servers recalculate and adjust your robot’s trajectory and speed every 10ms (P2OS v1.I and earlier) or every 5ms (P2OS1.J) based on feedback from the wheel encoders. Note that the latter time cycle leads to enhanced performance of the robot.

The default PID values for both translation and rotation are stored in FLASH. Beginning with P2OS1.J, you may change those values on the fly with the client commands 84-87.

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