Okuma OSP 5000, Электротехническое обслуживание, Учебное пособие

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Okuma America Corporation
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Rev. 8-21-01
FEEDBACK DEVICES
A CNC control needs some kind of feedback from its servo systems in order to control the
machine’s axes accurately. A feedback device provides speed and positioning information. The
following is a summary of the different types of feedback devices found on Okuma machines
with the 5000 series control. A brief description of each type is also included.
The early 5000 controls have DC drives as mentioned earlier in this section. The LDU 600 and
LDU TR utilize a tachometer and a D6 absolute position encoder for axis speed and position
feedback. The SDU 600 utilizes a tachometer and a pulse generator for spindle speed and
position feedback.
All the other Okuma axis drives which use the BL motor have an absolute position encoder
(E,F,FB,or FC) for speed and position feedback. Some machines utilizes MPR’s or Inductosyn
transducers along with the absolute position encoder for high accuracy positioning.
All of the Okuma AC spindle servo systems utilize a resolver and a pulse generator for speed and
position feedback. The Fanuc spindle servo system is the only exception. It utilizes an optical
encoder instead of a resolver for motor speed feedback.
Some of the Okuma lathes have TCC resolvers which are used to control turret positioning.
Some of the latest lathes have turrets that are driven by a BL motor which have an HC type
absolute position encoder.
Tachometer
Commonly referred to as a tachgenerator this type of device is used for velocity (speed) feed-
back. This device generates a DC voltage. On Okuma machines, the tachgenerator is used to
monitor actual motor speed. The faster the DC motor turns the higher the DC voltage level. If
the rotation direction is changed, so will the polarity of the voltage generated by the
tachgenerator. Most tachgenerators are rated for a certain voltage level. For example, if a
tachgenerator is rated at 7v/1000rpm, the voltage generated by the tachgenerator will be 7 vdc
when the motor is turning at 1000 rpm, 14 vdc when the motor is turning at 2000 rpm and so on.
This voltage signal should be a DC level, with very little noise or ripple. Most tachgenerators
used on the Okuma axis drive motors are rated at 7 volts per 1000 rpm and 20 volts per 1000
rpm for the SDU 600. The voltage that the tachgenerator is rated at can be determined by
looking at the characteristics sheet for the axis or spindle drive in question. Again, this type of
feedback device is found on any machines with DC spindle drives.