TECHNICAL REFERENCE
449
June 1999
96-8000
12.5 SERVOS B RUSH / BRUSHLESS
SERVO E NCODERS
Haas machines are equipped with brushless motors, which provides for better performance, and no mainte-
nance. In addition to the performance differences, these machines differ from brush type machines, which have
already been discussed, in the following areas:
The brushless motors have 8192 line encoders built in, which result in differences in acceleration parameters 7,
21,35,49 and 157. The exponential accel/decel time is set by parameters 115, 116 and 168. "In Position"
parameters 101, 102, 103, 104 and 165 also affect brushless motors.
The motor controller board has a dedicated processor which does all the servo control algorithm.
There is no servo distribution board anymore, therefore there is no CHARGE light present. Care should still be
taken however, since there are high voltages present on the amplifiers, even when power is shut off. The high
voltage comes from the spindle drive, which does have a CHARGE light.
The servo drive cards are replaced by Brushless Servo Amplifiers, and are controlled differently.
A low voltage power supply card is added to the servo drive assembly to supply the low voltage requirement to
the amplifiers.
The CNC software is version 9.xx.
The user interface and motion profiling have not changed however, and the user should not see any functional
differences between a brush type machine and a brushless machine.
SERVO C HARACTERISTICS
Servo characterstics are explained in detail in the previous chapter. The following is an example of how to
achieve 130 inches/minute.
The exponential accel/decel time constant is set by Parameters 113, 114, 115, 116 and 168. It has units of
0.0001 seconds. The speed limit at which exponential accel/decel is not available is defined by the relationship
between Parameters 7 and 113 (for the X-axis). Thus if Parameter 7 is 8000000 steps/sec/sec and Parameter
113 is 375 (0.0375 seconds); the maximum velocity for accurate interpolation should be:
8000000 x 0.0375 = 300000 steps/second
For an 8192 line encoder and 6 mm screw, this would be:
60 x 300000 / 138718 = 130 inches/minute
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