Each roller/spring combination is suspended by a single leaf spring which is supported and anchored to the concrete drum of the building. The drive rollers are each connected via an intermediate chain drive through a helical/wormdrive gearbox to the TASC unit which provides an infinitely variable speed and torque control.
The dome shutters are of the bi-parting type and are constructed in the same way as the dome. They open and close on roller guideways on their top and lower faces. These guide roller assemblies are supplemented by sets of lift-off rollers which prevent the shutters from being displaced by wind or other effects. The shutters are opened and closed by a synchronising drive system which open the shutters until limit switches are activated. The DOME push buttons on the control desk indicate whether they are in an OPEN or CLOSE position. A windshield is also available to reduce wind in the dome due to gusts. If the wind speed exceeds 50 km/hour, the dome shutters MUST be closed.
The dome, shutters and windshield can be operated in LOCAL mode from the observing floor, but for operation from the control room the switches on the local control box MUST be switched to REMOTE.
Position encoding for the dome is achieved using a 10 bit absolute T + R encoder mounted on a bracket fitted to the wood paneling above the control room. This is spring loaded and the encoder is driven through a gearbox and sprocket which runs in an endless chain attached to the dome. A line driver box mounted on the encoder bracket sends position information to CAMAC.
Three phase power for the shutter motors, windshield and dome crane is supplied to the dome through slip rings.
PR2402 Input register
Address: B4 C2 N10 A0 Reads position data from the dome encoder
OD2407 Output driver
Address: B4 C2 N11 A0 Dome drive (CW and CCW directions)
Address: B4 C2 N11 A1 Dome speed
See the JKT CAMAC manual for more details
Full information on the JKT dome can be found in:
JKT Technical manual: 13
JKT Technical manual: 14 JKT Dome control circuits
If in doubt (and with the TCS running), drive the dome to 235o and check that the marks line up. If this is NOT the case, using the manual +/- dome direction buttons, rotate the dome until the marks line up then read the ACTUAL dome position from the TCS Info Display window. To re-align, pull back the encoder to disengage the spocket and rotate it by hand until the position reads 235o . Once achieved, re-mesh the sprocket (without moving it) back into the chain.
A poled rotor which is fixed to the output shaft is surrounded by a tube which is driven by a constant speed AC motor. A stationary brushless coil is held on a stator fixed to an outer casting. Magnetic flux is set up when the field coil is energised which generate eddy currents in the tube and cause the rotor to revolve. A tachogenerator is mounted to the output shaft of one of the drives to generate a voltage proportional to speed. Cooling air is provided by a constant speed fan driven by the motor.
Velocity control is achieved by comparing a reference voltage supplied by the speed control potentiometer (always set to maximum)with a feedback signal from the tachogenerator. Differences between these voltages cause the output drive circuit to supply a varying current to the excitation coil thereby maintaining the set speed constant. Additional facilities are provided to control the acceleration and torque. Refer to the TASC unit technical manuals for further information.