The block diagram for FPS system is as shown in fig:
fig.3The feed drive motor is coupled to the feed turret through two stages of gear reduction,first is a worm gear with 300:1 reduction and second one is primary bull gear with 5:1 reduction, Thus total gear reduction is 1500:1. The incremental encoder is used for marking the position. As shown in the figure the encoder is connected to the output shaft of the worm gear reduction .This means that for one complete rotation of the turret,the encoder rotates for 5 times.Encoder gives the direction and count signals which acts as a position feedback to 8051FA microcontroller.The cpu card is based on 8051FA microcontroller. 8051 has inbuilt serial port through which it communicates to the antenna base computer through RS485 link.Microcontroller 8051FA gives the command signals like direction, RGSO and PWM to the drive card which drives the MOSFET bridge to rotate the motor in proper direction and set speed and thus feed is focussed with an accuracy of one arc minute pointing.
Due to the above bull gear and gear box arranement of the feed ,when feed completes
one rotation (rotation through 360 degrees) ,encoder goes through five rotations.Encoder generates 4096
pulses during one complete rotation.thus a complete rotation by feed system will generate
20480 encoder pulses .One pulse from the encoder thus corresponds to 0.0175
degree rotation of the feed(i.e approximately one arc minute).
These encoder pulses are counted by the microcontroller to determine the angular displacement of the feed system .
1 rotation of encoder = 4096 pulses
5 rotations of encoder = 20480 pulses
1 rotation of feed = 5 rotations of encoder
360 deg rotation of feed = 20480 * 2 pulses from encoder
1 pulse = 360 / (20480 X m)
m = multiplication factor(implemented in software) = 2
1 pulse = 1.054 min
Thus feed can be focussed with the resolution of 1.05 min ,theoretically.