Velocity (Oscillator) Mode

In velocity mode, the motor's speed is controlled by analog and digital inputs. If you have used an Applied Motion "O" or "PDO" drive in "oscillator mode", you're in the right place. The ST, STM and STAC drives can do everything the "O" and "PDO" drives can do and more.

You can use velocity mode on any ST, STM or STAC model, but the setup is different on certain models because these drives have fewer inputs and outputs than the other models.

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Using Velocity Mode with an ST5-S, ST10-S, or STM

Using Velocity Mode with all others drives

Using Velocity Mode with an ST5-S, ST10-S or STM

The Velocity Dialog for these drives allows you to set up the drive for velocity mode and configure all available I/O.

- Check the box marked "Use X1/STEP input as Run/Stop" if you want to command the drive to run using a switch or a signal form another electronic device. If you do not check this box, the motor will run at all times (unless you have also chosen "Speed proportional to analog input" and the analog input voltage is at 0.)
- Input X2/DIR always controls the motor direction. The analog input can also change the motor direction if you have an offset (see Advanced Settings, below)

Options for EN include:

- Change motor speed - when closed, the motor will run at a different speed, which you must enter to the right of the "Change motor speed to"
- Enable motor when
- Enable motor when open - opposite of above Reset alarm when closing - EN can be used to clear an alarm or fault by closing it
- Reset alarm when opening - EN can be used to clear an alarm or fault by opening it. Also re-enables the motor.
- Not Used - not automatic function for EN, but its state can be read using the SCL IS command. Can also be used by SCL FS and FY commands.

Options for the output are:

- Closed on fault - output will close if a fault occurs
- Open on fault - output is normally closed and opens if a fault occurs
- Closed to release brake - output controls a fail safe brake relay
- Open to release brake - same as above but output opens to release the brake
- Closed when moving - output closes whenever motor is moving
- Open when moving - output opens whenever motor is moving
- Tach out - output produces pulses relative to the motor position
- Not Used - output has no automatic function but can be controlled by the SCL SO, FO, IH and IL commands.

Using Velocity Mode with all other drives

All of the signals you'll need for velocity mode connect to the IN/OUT1 connector. Please refer to the hardware manual for details.

If you simply want the drive to run at a constant speed anytime it is on, uncheck all the boxes, enter a speed in the text box and an accel rate in the accel box. As soon as you download your configuration, the motor will run

In most applications, you'll need to stop the motor. The simplest way to do this is to check "Use X1/STEP as the run/stop input." When the X1 input is closed, the motor will accelerate to the speed you've chosen at the acceleration rate you entered in the "Accel" box. When X1 opens, the motor decelerates to a stop using the value in the "Decel" box.

If you need two speeds, check "If X5 closed, change speed...". This option allows to you to enter a second speed. The motor will accel or decel to the second speed anytime X5 is closed. When X5 opens, the motor speed changes to the first speed, again according to the accel and decel rates you've entered.

Need more speeds? These drives include an analog input that can be used to set the speed when X5 is open or not used. Just select a voltage range to match your signal (0 to 5 V, 0 to 10V, +/-5V or +/-10V), then enter a speed that corresponds to the speed you want at your maximum input voltage. If you apply less than the maximum, the motor speed will be proportional to the applied voltage.

If you plan to use a potentiometer to adjust the speed, it's best to select "0 - 5V" as the range, then connect the drive's 5V power output to the potentiometer's "cw" terminal.

If you want to use a joystick to operate the drive in both directions, you'll need to enter an offset that is half the voltage range. If you're using the drive's 5V output to power your analog joystick, set the offset for 2.5V. Click the "Advanced Settings" button to change the offset.

Direction

The X2 input is used to select the direction of rotation. If the motor is moving when you change the state of the direction input, the motor will decelerate to stop then accelerate to the same speed in the opposite direction.

Motion Output

Output Y2 can be used to tell another piece of electronics when the motor is moving in velocity mode. If you want the signal to indicate when the motor is in motion you have two choices: Y2 can be closed when the motor is moving and open when it is stopped, or Y2 can be open when moving and closed when stopped. If you want a tachometer output (a signal proportional to the motor speed), Y2 can emit pulses as the motor turns, 100 square wave pulses per revolution (assuming you have a 1.8° motor, otherwise you get 2 times the motor electrical frequency).

Additional settings of 200, 400, 800 and 1600 pulses/rev are available for drives with DSP firmware version 1.02 or later. However, the tach output’s maximum frequency is fixed, so the integrity of the tach output signal at higher resolutions is dependent on motor speed. Suggested speeds ranges for the different tach output resolutions are shown in the table below.

tach ppr | accurate at speeds
100 | 0 - 50 rev/sec
200 | 0 - 25
400 | 0 - 12.5
800 | 0 - 6.25
1600 | 0 - 3.125

Note: Signal integrity is best with an 80 mA load (use 300 ohms at 24V, 150 ohms at 12V or 62 ohms at 5V.)

Advanced Analog Settings

- Deadband: If you need your analog signal to be able to stop the motor, but the signal doesn't quite go to zero volts (potentiometers can usually go to zero volts, but electronic circuits usually can't) then you'll need a "deadband". This is the range of voltages in which the motor does not run. It is specially useful to get the motor to stop when you let go of the joystick.
- Offset: This setting is most often used for a single ended (unipolar) joystick. With such a device, the output signal is typically 0V when the joystick is pressed to one extreme, 5 volts at the other extreme and 2.5 volts when at rest in the center. By entering an offset of 2.5 volts, the motor speed with be increasingly clockwise as the joystick is "pushed forward" and increasingly counterclockwise when the "pulled back" from it's neutral position.
- Filter Frequency: If your analog signal is noisy you may notice the motor speed changing when it should be constant. It is not unusual for industrial systems to pick up some electrical noise on an analog wire and the ST's high resolution 12 bit analog input may respond to the noise. In that case you should lower the analog filter frequency (in the "Advanced Settings" dialog) until the problem goes away. If you set the frequency too low, the motor may change speeds more slowly than you specified in the accel and decel boxes because of excessive filtering, so try not to overdo it.