APC AP9212 User's Guide download pdf (Page 17)

Each servo motor is powered by its own DC servo amplifier which receives an analogue voltage

from the Macrostation (see 2.6.4).

In October 2002, the motors were upgraded to improve the average telescope slew time from

approximately 120 seconds to 30 seconds for a 100 degree slew.

Connected to each motor, is an Incremental

Encoder (Figure 2-6), which is used to accurately

measure the shaft rotation.

Once calibrated, the information from these

encoders is used to calculate the coordinates of

the telescope.

Also in October 2002, newer encoders were

installed providing a higher resolution of 10000

pulses per revolution, four times higher than the

old encoders.

2.6.1 Anti backlash motor

The Anti backlash motor is required on the declination axis in order to compensate for the

backlash caused by the use of a worm gear, rather than a friction drive system, as used in the

right ascension axis.

The declination motor, is mounted perpendicular to its axis (as shown in Figure 2-5).

Consequently, a worm gear is used to correctly transfer the motion of the motor to the main

gear.

The slack space between the teeth of these gears results in a backlash. This is particularly

noticeable when the motor changes direction, a small amount of motion on the motor will result

in no movement of the telescope. Also, the telescope mount can be moved freely by physically

Figure 2-4 Right ascension motor

Figure 2-5 Declination motor

Figure 2-6 Incremental encoder

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APC AP9212 User's Guide Page 17