Pulse & Direction Mode - Flex IO

Pulse Input Mode is for systems whereby the position of the motor is determined by a digital input signal in the form of pulses.

The three modes available are :
 

Pulse and Direction. Accepts a signal such as that generated by an external indexer or motion controller. With this mode the frequency of the pulses fed into one input determines the speed, the direction of rotation is determined by a signal fed into another input.
 

CW and CCW Pulse. The motor will move CW or CCW depending on which input the pulse is fed into. The drive has two inputs allocated to this feature, pulses fed into one input will generate CW motion, pulses fed into the other input will generate CCW motion.
 

A & B Quadrature. The motor will move according to signals that are fed to the drive from a master encoder. This encoder can be mounted on a shaft on the machine or it can be another motor in the system. The master encoder must be 2-channel, incremental.

For all the Pulse Input modes you will need to determine a value to enter into the "Steps/Rev" box, an explanation on how to do this is given in the next section.  

Steps/Rev

Allows you to adjust the way that the drive responds to incoming step pulses. This is useful if you are replacing a step motor drive in an existing application with an STM, because you can make the new drive have the same number of steps/revolution as the old one.

If your application is new, you should choose a value that makes sense for your pulse source, or indexer. The motor will provide smoother, more precise with a higher step count, but if the frequency of your indexer is limited you may have to reduce the steps/rev to get a speed range you want. For example, if your application calls for a maximum speeds of 20 revs/second and your indexer is limited to a 100 kHz maximum pulse rate, you won't want to set the steps/rev higher that 5000.

Another reason for choosing a particular value is to make one step result in a convenient increment of motion. For example, you may have a linear motion application using a lead screw and the screw pitch is 5 turns per inch, then 20,000 steps/rev will provide a nominal movement of .00001 inches per step. That will make it easier to calculate move lengths. If you wanted to work in metric using that same leadscrew, you could set the STM for 50800 steps/rev and get .0001 mm per step.

Steps/rev is also important in encoder following applications. If you want to move the motor two turns for every one turn of a 2000 count/rev (500 line) encoder, you would choose 1000 steps/rev.

Step Smoothing Filter

If your application requires the drive to accept pulse & direction signals from a low speed motion controller, you may have to set your drive for a low step/rev setting such as full step (200 steps/rev) or half step (400 steps/rev) in order to achieve the motor speeds you desire. In such cases, the step smoothing filter can provide smoother, quieter motion than is normally possible with a full or half step drive. Some experimentation may be required for your application, but 50 Hz is usually a good place to start.

Note: the step smoothing filter, like most filters, creates a delay in the output (in this case the output is the motion of the motor and load). For many applications, this delay is not important unless the motion is tightly synchronized to other devices or processes. The figure below illustrates the time delay that results from changing the step smoothing filter from 1000 Hz to 50 Hz. The entire move profile is delayed by about 45 milliseconds.

Input Noise Filter

If you are experiencing position errors or the motor is behaving erratically, the drive's high bandwidth step input may be experiencing the effects of electrical noise. If so, lower the input noise filter frequency until the problem is eliminated. Please keep in mind that lowering the frequency limits the top speed that the drive can achieve.

For square wave signals (where the low pulse and high pulse are equal), set the filter to four times your maximum pulse rate.

For example, if the maximum speed of your application is 10 rev/sec and the drive is set for 20,000 steps/rev, the filter frequency should be

(10 rev/sec)(20,000 steps/rev)(4) = 800,000 Hz = 0.8 MHz

If the maximum speed is 10 rev/sec and the drive is set for 2000 steps/rev, use this frequency:

(10 rev/sec)(2000 steps/rev)(4) = 80,000 Hz = 0.08 MHz

Some pulse sources are not square waves.  Instead they have a fixed width low or high pulse and the time between pulses determines the speed.  For fixed width pulses, use this formula:

F = 2 / pw, where F is the noise filter setting in MHz and is the pulse width in microseconds.

For example, if the pulse width is 5 microseconds, set the noise filter to 2 / 5 = 0.4 MHz.

Other I/O Settings

You can also assign functions to the third input and fourth I/O points.

Options for I/O#3 include:

• Enable motor when closed (the motor is enabled when current is flowing into the input and is disabled when no current is flowing)
• Enable motor when open - opposite of above
• Reset alarm when closing - I/O#3 can be used to clear an alarm or fault by closing it.   Also re-enables the motor.
• Reset alarm when opening - I/O#3 can be used to clear an alarm or fault by opening it.   Also re-enables the motor.
• General purpose input - no automatic function for I/O#3, but its state can be read using the SCL IS command. Can also be used by SCL FS and FY commands.

Options for I/O#4 are:

• Closed on fault - I/O#4 will close if a fault occurs
• Open on fault - I/O#4 is normally closed and opens if a fault occurs
• Closed to release brake - I/O#4 controls a fail safe brake relay
• Open to release brake - same as above but I/O#4 opens to release the brake
• Closed when moving - I/O#4 closes whenever motor is moving
• Open when moving - I/O#4 opens whenever motor is moving
• Tach out - I/O#4 produces pulses relative to the motor position
• General purpose output - I/O#4 has no automatic function but can be controlled by the SCL SO, FO, IH and IL commands.