Basic Parameter Settings; Zero Point Return Function - Mitsubishi Electric Melsec FX Series Beginners Manual

Positioning controller
3.1.2

Basic parameter settings

To send a series of pulses (a pulse train) to a servo amplifier, positioning controllers use a specified
feed quantity, which is proportional to the number of pulses. A feed speed must also be specified to
control the number of pulses output per second.
Feed quantity
The feed quantity determined by the target address tells the servo system how far to move the
workpiece. So, for example, if a servo motor encoder generates 8,192 pulses for one rotation, the
command pulse number "8,192" can be output to rotate the servo motor by 1 rotation.
Feed speed
The feed speed defines the amount of travel per unit of time for the workpiece. When a servo motor
encoder generates 8,192 pulses for one rotation, the command pulse frequency (speed) "8,192
pulses/s" should be output to rotate the servo motor by 1 rotation per second. Decrease the pulse
frequency to rotate the servo motor at a lower speed. Increase the pulse frequency to rotate the servo
motor at a higher speed.
Acceleration/deceleration time
When the start command is given, acceleration, operation at constant speed, and deceleration are
performed for positioning. Set the acceleration time and the deceleration time in the controller's
parameters.
Actual
acceleration
time
3.1.3

Zero point return function

Many positioning systems include a "home position" to where a workpiece may need to return after
performing various operations. For this reason, positioning controllers include a built-in function to
return a workpiece to a defined position by using a mechanical DOG switch.
To understand how this works, it is necessary to first understand when the function is needed
according to the parameter setting of the servo amplifier and the type of servo motor encoder.
Incremental type servo motor encoder (pulse count method)
When the servo system uses an incremental or relative type encoder, the current value of the address
stored in the position controller is not "remembered" or maintained when the power is turned off. This
means that the address is set to zero every time the power is cycled, which can be disadvantageous
in an application. Accordingly, every time the system is re-powered, it must be calibrated to the
correct zero-point location by executing the zero point return function.
FX Positioning Control Systems
Parameter:
Max. speed
Speed
Positioning speed
Parameter: Parameter:
Acceleration Deceleration
time time
Components of Positioning Control and their Roles
Fig. 3-4:
Actual
deceleration
time
Positioning pattern of
acceleration/deceleration time
312010da.eps
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