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8. CALCULATION METHODS FOR DESIGNING
8.3 Speed and command pulse frequency
The servo motor is run at a speed where the command pulses and feedback pulses are equivalent.
Therefore, the command pulse frequency and feedback pulse frequency are equivalent. The relation
including the parameter settings (CMX, CDV) is as indicated below (refer to the following diagram):
f
0
CMX
CDV
Pt
N
0
60
..................................................................................................................................... (8.4)
CMX
CDV
f
0
Electronic
gear
Feedback pulse
frequency
Servo motor
f0 :Command pulse frequency [pps]
CMX :Electronic gear
(Commanded pulse multiplication numerator)
CDV :Electronic gear
(Commanded pulse multiplication denominator)
N
0 :Servo motor speed [r/min]
Pt :Number of feedback pulses [pulses/rev]
(Pt 8192 for HC-MF)
According to Equation 8.4, the following equations may
be used to obtain the electronic gear and command
pulse frequency to rotate the servo motor at No.
Electronic gear
CMX
CDV
Pt
No
60
1
f0
............................................................................................................................................(8.5)
Command pulse frequency
f0 Pt
N
0
60
CDV
CMX
...........................................................................................................................................(8.6)
[Setting example]
Obtain the command pulse frequency required to run the HC-MF at 3000r/min.
When the electronic gear ratio 1 (initial parameter value) is used, the following result is found according
to Equation 8.6:
f
0 8192
N
0
60
CDV
CMX
(Command pulse frequency)
8192
3000
60
1
409600[pps]
However, as the maximum input command pulse frequency in the open collector system is 200kpps, for
general-purpose servo 409600pps cannot be entered.
To run the servo motor at the speed of 3000r/min at not more than 200kpps, the electronic gear setting
must be changed. This electronic gear is found by Equation 8.5:
CMX
CDV
8192
3000
60
1
200 10
3
(Electronic gear)
256
125
Therefore, the parameters are set to CMX
256 and CDV 125.