Aerotech UNIDEX 100 Troubleshooting Guide

In the upgrading and transformation of precision automation production lines and old equipment, the Aerotech UNIDEX 100 (and U100i with only control board), as a classic single axis programmable motion controller, is still in service in many semiconductor, electronic manufacturing, and precision machine tool equipment today with its powerful DSP56002 digital signal processor and flexible multitasking operating system. This series of controllers can seamlessly drive stepper motors, DC brushed servo motors, and AC brushless servo motors. However, as the service life of equipment increases and the complexity of the on-site electrical environment increases, engineers often face thorny issues such as communication abnormalities, motor loss of control, or parameter loss when maintaining such equipment. This article is based on the hardware architecture and control logic of the controller, providing you with a detailed set of on-site troubleshooting and optimization guidelines.

Hardware initialization and communication link troubleshooting

When the UNIDEX 100 system fails to power on, loses programs, or experiences communication interruptions with the upper computer, the fault points are often concentrated in the power module, core card jumpers, or communication parameter configurations.

1. The system cannot start or crashes abnormally

Firstly, check the AC Line Fuse on the back of the chassis. If the fuse is intact and the fan is running, but the system cannot start, it is necessary to focus on checking the 5V power supply fuse on the control board. If the external circuit (such as a sensor powered through pin P2-30) is overloaded, it will directly cause 5V power protection. In addition, the JP 2 jumper on the control board is a fatal point that is easily overlooked: if JP 2 is not plugged into pins 2-3, the system will not only fail to start normally, but also experience operational abnormalities.

If the system’s memory data is damaged due to the installation of new software or battery failure (manifested as the inability to store or download programs), a forced hardware reset (SETUP) must be performed. Disconnect the main power supply and use a jumper to short-circuit pin 19 (Setup n) and pin 16 (Common) of the I/O interface (P2); If P2-20 is not connected to an external power source, it is necessary to short-circuit P2-20 to P2-30 (5V). After being powered on for about 5 seconds, power off and remove the jumper, and the controller parameters can be restored to the factory default values.

2. Communication failure between RS-232 and RS-422

If the upper computer cannot establish communication with the controller, first confirm the hardware configuration of the controller. The standard configuration is usually RS-232-C. If RS-422-A interface is used on site, it must be specified at the time of ordering, as the corresponding differential chip may not be installed on the control board.

The most common reasons for RS-232 communication are baud rate, data bit, or stop bit mismatch. Check the communication parameters (PRM: 001 to PRM: 004) through the panel or upper computer software, and if necessary, perform the SETUP process described above to restore the default communication parameters. In addition, if using the RS-232 Daisy Chain mode, it is necessary to ensure that the address character (PRM: 004) of each node is unique and correct, and to pay attention to correctly closing or opening the loop by sending space characters.

Common faults in motor drive and feedback circuits

The core of a motion controller lies in precise driving and closed-loop feedback. When the motor experiences no torque, runaway, or frequent alarms, it is necessary to start with jumper configuration and physical wiring.

1. The “flying car” phenomenon of DC brushed motors

When controlling a DC brushed motor in speed loop mode, if the motor rotates uncontrollably at high speed (runaway), it is usually caused by the following two reasons:

JP8 jumper error: If the controller is configured for speed command mode, JP8 must be installed on pins 2-3 and ensure that the resistor capacitor network (RCN1) is correctly installed.

Reverse polarity of the tachometer: The feedback polarity of the tachometer generator (Tachometer) is opposite to the command polarity, causing the system to form positive feedback. Please immediately turn off the power and swap the wiring of the speedometer on the P3 interface.

2. The motor has no torque or frequently reports drive faults

Current limit jumper mismatch: The UNIDEX 100 sets the maximum output current (up to 20 Amps) through three jumpers, JP13, JP18, and JP19. If the set jumper limits the current and the program (PRM: 201, PRM: 216, etc.) requires a larger current, the motor will be powerless due to current limitation. Please strictly match the jumper according to the motor nameplate.

Motor type jumper error: JP16 and JP17 must be configured correctly according to the connected motor type (stepper, DC brushed or brushless AC). Connecting the wrong jumper can cause confusion in the commutation logic.

Brushless motor commutation failure: If the AC brushless motor has no torque, first check if the Hall Effect sensor is correctly connected to pins 5, 10, and 11 of the P3 interface. Even if the position feedback encoder is connected to the P4 interface, the Hall sensor must still be connected to P3. Secondly, check if the PRM: 239 (brushless commutation type) parameter settings match the motor.

Hardware circuit breaker: Check if the motor fuse (F1) on the panel is blown. At the same time, if the device frequently reports errors during rapid deceleration, it may be due to excessive feedback energy from the busbar causing the drain fuse F4 on the power board to burn out. It is necessary to check the drain circuit and the threshold setting of potentiometer R2.

3. Limit and sensor false triggering

The system reports a limit fault without encountering a physical limit, usually due to a mismatch between the normally open/normally closed logic of the hardware limit and the polarity of the software. At this point, it is necessary to check PRM: 317 (Error State Reverse Mask). For low-level effective hardware limits, Bit 8 and Bit 9 need to be set to 1; If the high level is valid, set it to 0.

Servo loop optimization and multitasking synchronization

For precision applications using DC brushed or AC brushless servos, the tuning of the PID loop (position loop and velocity loop) directly determines the dynamic performance and positioning accuracy of the equipment.

1. PID parameter tuning steps

Before adjusting the gain, it is recommended to turn off the speed feedforward (PRM: 222=0) and keep the integration switch normally closed (PRM: 214=0). Firstly, set the position gain Kpos (PRM: 220) to a smaller value (such as 0.01 to prevent drift), and keep the velocity proportional gain Kp (PRM: 218) at its default value (10000).

After power on, gradually increase Kp until the motor load shows sufficient rigidity. If you hear a “rustling” quantization noise from the motor, it indicates that Kp is too high and needs to be adjusted back to the critical point where there is both rigidity and no noise. Subsequently, send short-range positioning instructions through MDI mode, slowly increasing Kpos (PRM: 220) until the position response is rapid and there is no overshoot. Finally, in order to eliminate steady-state errors caused by load friction, an integral gain Ki (PRM: 219) is introduced, which increases from a small value (such as 10) until the “In Position” indicator light can quickly light up after the command ends (not exceeding 0.25 seconds). If the motor exhibits low-frequency oscillation when stationary, it indicates that the Ki value is too high.

2. Use an oscilloscope to observe dynamic response

Engineers can map the speed feedback (REG: 205) to the analog output port (DAC() command, corresponding to pin P2-17) by writing a simple test program, and use an oscilloscope to observe the waveform during acceleration and deceleration phases. If the waveform overshoot is severe, Kpos should be appropriately reduced; If the waveform appears as a staircase or burr, it is necessary to consider whether the encoder resolution is too low or there is a gap in the mechanical transmission.

3. Data protection for multitasking systems

The UNIDEX 100 adopts a multitasking (Task 1 and Task 2) time-sharing mechanism, which is very suitable for monitoring I/O status while executing motion instructions. However, when sharing floating-point variables (FV) or long integer variables (LV) between two tasks, data tearing (some bytes being modified) is highly likely to occur. Be sure to add the SYNC command before the instruction to access the shared variable. SYNC will force the current instruction to complete before task switching, ensuring data consistency.

Deep application investigation of encoder and I/O interface

In flying scissors, color code positioning, or complex synchronous tracking applications, engineers often use the hardware comparator function of encoder chips to achieve microsecond level signal output.

1. The comparator and the borrow/carry output do not trigger

If using primary/secondary encoders for position capture or triggering external devices, attention should be paid to the settings of jumpers JP22 and JP23. If a comparator (COMP/COPPT) is used, the jumper should be short circuited 1-2; If borrowing/carrying (BW/CY) is used, short-circuit 2-3.

In addition, it must be clarified that if a certain encoder port has been used by the system for position or velocity feedback, its counter hardware resources will be exclusively owned by the system and cannot be used for external custom comparison triggers. At this point, the external triggering task should be assigned to another idle encoder channel.

2. Abnormal analog input and output

If the controller cannot read the analog signal input through P2-35 (such as a proportional joystick), please check if P2-20 (input common terminal) is correctly connected to the 5V power supply or the ground wire of an external power supply to power the optocoupler isolation circuit. Similarly, when there is no response from the external relay, it is necessary to check whether P2-25 (output common terminal) has been connected to the external power supply and confirm whether the pull-up resistor is configured correctly.