Toshiba Aquilion 16: patient table deck drive jams periodically
What happened
On a Toshiba Aquilion 16 the horizontal deck drive of the patient table intermittently jams and the servo driver reports error 21 (encoder communication loss), mostly at night. De-energising the drive and moving the deck by hand restores movement, but the table cannot be switched to manual mode from the gantry panel.
What was checked
- The engineers pulled, cleaned and reseated the encoder.
- They checked the mechanics for obstructions, and lubricated and adjusted the rollers and bearings.
- They verified the servo drive supply and reset the KGSTM board, after which the table worked again.
- They discussed a mismatch between the two encoders — the external one on the gearbox shaft and the one built into the motor.
Cause
Not finally confirmed. The working theory among the engineers is that the electromagnetic brake between the motor and the gearbox slips, so the readings of the two encoders diverge and the drive reports encoder communication loss.
The cause is probable and was not fully confirmed.
What was done
Since the fault kept returning after cleaning and mechanical servicing, the engineers recommended replacing the complete drive (servo motor with gearbox); a servo motor (two modifications) and a servo amplifier were reported in stock. The outcome is probable — the root cause was not confirmed.
Safety
Before opening the drive, isolate the table from the mains and treat the heavy deck as a stored-energy hazard that can coast or drop, and verify the emergency stop, the manual release and electrical safety before returning the table to use.
Lesson: When an encoder error returns after cleaning and mechanical service, compare the readings of both encoders and look for anything that breaks the mechanical link between them, such as a slipping brake — resets only postpone the failure.
Covered in the course: CT Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.