AN1794 datasheet(8/34 Pages) STMICROELECTRONICS

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Stepper motor drive

AN1794

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Stepper motor drive

After the system has established the connection to the interface board, it will initialize the

settings to the last stored settings and open the appropriate GUI for the selected motor type.

For the Stepper motor, the system can operate in either a constant speed or positioning

(indexing) mode. The constant speed mode can easily be used to see that the system is

working.

3.1

Constant speed mode

Speed control screen: a large blue button at the bottom of the screen should read,

"switch to INDEXING MODE". If the button reads, "switch to SPEED CONTROL

MODE", click the button once to go to speed control mode.

Stepping mode: in the stepping mode box, select either Normal or Half Step.

Microstepping mode is only available when using the L6208.

Device selection: in the device selection box, select the device being evaluated.

direction: in the direction box, click the toggle switch to pick forward or reverse. This is

somewhat arbitrary since we probably don't know what the direction sense of the motor

will be. Once the motor is running, toggle this switch to reverse the motor direction if

desired. To reverse the meaning of the forward and reverse designations, disable the

motor (orange disable button at bottom of screen) and then swap the motor wires at

either CN3 or CN4.

Decay mode: only the L6208 allows the selection of fast or slow decay. Set the toggle

switch to slow decay.

Accel rate: set the accel rate to about 1000 steps per second per second (steps/sec2).

In the practiSPIN system all motion parameters are given in terms of the basic units of

steps and seconds: position in steps, velocity in steps/sec, and accel/decel in

steps/sec2. In order to relate these settings to rotations, RPM, and RPM/second it is

necessary to know the number of steps (or half steps) per rotation for the stepper motor

being used. A common value is 200 steps or 400 half steps per rotation.

Running speed: set running speed to about 100 steps/sec.

Decel rate: set decel. rate to about 1000 steps/sec2.

Accel current: set accel current to about 25%. This is an initial guess as to the required

setting and may need further adjustment. Generally higher accel rate settings require

higher accel current settings so that the stepper motor does not start to "slip poles" and

fall behind the desired position. Since we have initially set the acceleration rate setting

quite low, 25% is probably adequate.

10. Running current: set the running current to 25%. In practice the running current can

often be set to a lower value than the accel current since the torque requirement is

generally less during the constant speed part of the move. A lower running current

setting can help to keep the device and the motor running cooler.

11. Decel current: set the decel current to 25%. Since friction aids in decelerating the motor

it may also be possible to set the decel current lower.

12. Holding current: set the holding current to 25%. Whenever the motor is stopped (after a

run,) this level of current will circulate in the motor so that it will hold position against

any mechanical disturbance.

AN1794 Datasheet(PDF) 8 Page - STMicroelectronics

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