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AN2044

APPLICATION NOTE

1 REQUIREMENTS

In operating a stepper motor system one of the most common requirements will be to execute

a relative move. The move will usually be specified as a fixed number of basic motor steps in

the clockwise or counter-clockwise direction. It is common practice to execute this move along

a trapezoidal shaped velocity vs. time profile.

This profile is determined by the number of steps to be moved and the required accel, decel,

and peak speed. Very often system designers require that a move be made in the shortest

time possible and in these cases the accel, decel and peak speed are set to the maximum that

the system can achieve.

Given the move distance, accel, decel, and peak speed requirement, a profile can be deter-

mined. Since the control structure of the practispin software is designed such that the velocity

and accel/decel rate can be changed at will, the task of pre-calculating the velocity profile boils

down to determining the position values where operation switches from accel to constant

speed and then from constant speed to decel. Since this is a relative move, we can assume

that motion starts at position = 0, time = 0, and velocity = 0. Figure 1 shows a typical trapezoi-

dal velocity vs. time profile

Figure 1. Trapezoidal Velocity vs. Time Profile

Let:

P

= total move distance in steps

P1

= steps required to accel from 0 to V

P2

= steps required to decel from V to 0

V

= peak velocity in steps per second (steps/sec)

V1

= average velocity during accel or decel

OPERATING PRINCIPALS FOR PRACTISPIN

STEPPER MOTOR MOTION CONTROL

AN2044/0904

Rev. 1