Motion 03 — Home, then move

Briefing

A carriage on a short rail is driven forward and backward by JOG_FWD and JOG_REV. An encoder sends ENC_PULSE for every 10 mm it moves, but it only counts distance, in either direction: at power-up the PLC has no idea where the carriage is. A home switch (HOME_LS, TRUE at the home end) gives the one place that is known. Press HOME_CMD and the carriage creeps in reverse until HOME_LS trips, then stops and HOMED_LAMP lights. The position count must be zero when the carriage is on the home switch. After that, MOVE_CMD drives forward 30 counts (300 mm) and lights IN_POSITION. MOVE_CMD must be ignored until the axis is homed. JOG_FWD_PB jogs forward while it is held. Beyond 400 mm the overtravel switch LIMIT_FWD trips (TRUE when tripped): forward drive must stop even if the button is held, FAULT_LAMP latches and homing is lost. (On a real machine a limit like this is normally wired normally closed, so a broken wire also reads as tripped. Here the tag is already inverted for you, TRUE meaning tripped.) Homing again, which drives in reverse and so is always allowed, clears the fault. STOP ends any move or homing. Training material. Follow your site procedures, local electrical code and the manufacturer's instructions. Lockout/tagout and a qualified person are required for real equipment. A real axis also needs an end-of-travel limit that cuts power independently of the PLC.

Objectives

• MOVE_CMD does nothing until the axis has been homed
• HOME_CMD creeps in reverse until HOME_LS, then stops and lights HOMED_LAMP
• The count is zero at home; MOVE_CMD then travels exactly 30 counts and lights IN_POSITION
• The overtravel switch stops forward motion, latches FAULT_LAMP and loses the homed state
• Homing again clears the fault; STOP ends any move or homing

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1MOVE before homing → nothing moves

   The axis position is not known yet

2. #2HOME_CMD → creeps in reverse, not homed yet

   Homing runs towards the home switch

3. #3Carriage at the home switch → stopped and homed

   Reaching HOME_LS ends homing and records it

4. #4MOVE after homing → drives forward

   A homed axis accepts the move

5. #5Move complete → stopped at 300 mm, in position

   Thirty pulses from home end the move

6. #6Jog into the overtravel switch → stops, fault, reference lost

   Forward drive is blocked by LIMIT_FWD even with the button held

7. #7STOP during homing → stops and stays stopped

   STOP ends homing

8. #8Overtravel, release, home again → fault cleared and homed

   Reverse stays available so homing can recover from a fault