LTI ServoOne Servo Troubleshooting Guide



LTI ServoOne Servo Troubleshooting Guide

In the field of modern high-end equipment manufacturing and precision motion control, the ServoOne series servo drives launched by LTI DRiVES (now part of Danaher Group) have become the preferred choice for industries such as packaging, printing, machine tools, and robots due to their excellent overload capacity, modular hardware architecture, and extremely high safety integration. This series covers a wide power range from 2A to 450A and is divided into ServoOne Junior (compact single axis), ServoOne single axis system (standard type), and ServoOne multi axis system that supports energy feedback.

For on-site engineers in the "search for solutions" phase, it is crucial to quickly locate the fault point and perform EMC compliant replacement operations when the equipment is facing safety circuit false triggering, DC bus overvoltage, encoder communication interruption, or emergency replacement of spare parts. This article will provide you with a detailed practical troubleshooting manual from four dimensions: safety function (STO), multi axis system maintenance, encoder interface debugging, and hardware replacement.

Deep analysis and troubleshooting of STO safety functions

One of the core highlights of the ServoOne series is its integrated security features. Both the standard STO (Safe Torque Off) and the optional Integrated Safety Control comply with EN ISO 13849-1 PL e and EN 61508 SIL3 standards.

On site debugging and diagnosis of STO function

The STO function prevents the motor from generating torque by cutting off the drive signal of the power stage without disconnecting the main power supply.

Interface check: For ServoOne single axis/multi axis systems, safety signals are usually connected to X8 terminals (ASI+/ASI -). When conducting on-site inspections, first use a multimeter to measure whether there is a 24V DC voltage between the terminals. If the voltage is lost, the driver will report a safety stop fault.

Safety loop closed-loop: The safety status of STO is usually output to the upper safety PLC through ASO1/ASO2 feedback contacts or Ready signal. If the upper computer reports "safety circuit not closed", it is necessary to check whether the feedback contact of X8 interface is stuck due to internal relay failure, or whether the external safety door switch is disconnected.

Integrated Safety Control (SafePLC S): For models equipped with integrated safety control (such as up to SO84.072), an independent safety program runs inside the drive. If a malfunction occurs, the SafePLC S software on the PC side needs to be used to connect to the Ethernet port of the driver and read the diagnostic logs of the safety controller. Common issues include cross short circuits in safety input channels (requiring dual channel redundancy) or loose Safe Cross Communication (SCC) network cables (SCC-04), which result in the inability to synchronize safety status between multiple axes.

2. Taboos for troubleshooting

Before conducting any safety circuit inspection, it is necessary to ensure that the motor has stopped rotating. Do not short-circuit the safety input signal for forced operation, as this will cause the device to lose its PL e level security protection, which is a serious violation of regulations.

Maintenance of Multi Axis Systems and Regenerative Power Supply (PSU)

The ServoOne multi axis system consists of a DC powered axis controller and a power supply unit (PSU) with a sine wave regenerative power supply. This design not only shares the DC bus, but also feeds back the braking energy to the grid, which is energy-saving and environmentally friendly.

1. DC bus overvoltage and undervoltage faults

Overvoltage: When a motor in a multi axis system suddenly stops or the load is lowered due to gravity, energy is fed back to the DC bus. If the feedback energy exceeds the absorption capacity of the power supply unit, the bus voltage will rise and trigger an overvoltage alarm. When troubleshooting, first check whether the incoming voltage of the power supply unit (such as SO84.040. S, etc.) is normal. Secondly, check if external braking resistors are configured in the system (if regenerative power mode is not used). For renewable power sources, it is necessary to ensure that the Mains synchronization signal of the power supply unit is normal, otherwise energy cannot be fed back.

Undervoltage: If the DC bus voltage drops, it is necessary to check whether the input main contactor of the power supply unit is engaged and whether the internal pre charging circuit is normal. Use an oscilloscope to observe the waveform of the DC bus. If there are severe fluctuations, it may be due to an internal short circuit in one of the inverters in the multi axis system or aging of the bus capacitor (such as the BG7 model 7200 μ F capacitor).

2. Maintenance of liquid cooling system

High power modules (such as BG3 and above) support liquid cooling. If the on-site report shows a "overheating" fault of the radiator, in addition to checking the coolant flow and temperature, it is also necessary to check whether there is leakage in the quick connector of the liquid cooling connection kit (LCS01). The coolant temperature should be controlled below 40 ° C and should not be lower than the ambient temperature by more than 10 ° C, otherwise it may cause a short circuit of condensed water.

Troubleshooting of encoder interface and motor feedback faults

ServoOne provides two encoder interfaces (X7 and X8), supporting multiple protocols such as Parser, SinCos, TTL, SSI, EnDat, and HIPERFACE DSL.

1. Hiperface DSL single cable technology

For LSP series servo motors, ServoOne supports Hiperface DSL single cable interface. This technology integrates encoder signals and motor temperature signals into a two-wire cable, greatly simplifying wiring.

Communication failure: If the panel reports "Encoder error" or cannot read motor parameters, first check if the shielding layer of the motor cable (such as KM13 model) is 360 degrees clamped on the grounding clamp of the driver. Secondly, check whether the encoder inside the motor is damaged due to overheating or overvoltage. The Hiperface DSL interface has extremely high requirements for impedance matching, and it is strictly prohibited to splice it randomly on non original cables.

Temperature sensor malfunction: If a "Motor temperature sensor error" is reported, the temperature sensor pins inside the cable need to be checked. If using a third-party motor, it is necessary to confirm whether the KTY or PTC sensor parameters match the ServoOne software configuration.

2. Second encoder and fully closed-loop control

When the X8 interface is configured as the second encoder input (option 2 technology package is required), it is commonly used for full closed-loop control of external grating rulers. If a "Position deviation" alarm occurs, check the signal amplitude of the grating ruler (usually a 1Vs sine wave). Use an oscilloscope to measure channels A/B. If there is amplitude attenuation or phase shift, it indicates that the reading head of the grating ruler is dirty or the cable is damaged. After replacing the grating ruler, it is necessary to perform commutation offset self-learning again.

Specification for replacement of critical hardware and EMC compliance

When replacing key components such as main power filters, reactors, or braking resistors, strict adherence to electromagnetic compatibility (EMC) requirements is necessary, otherwise it may result in equipment failure to pass acceptance or frequent interference with other equipment.

1. Main power filter and reactor

The EMC performance of ServoOne is highly dependent on external main power filters (such as EMC7.1-UR to EMC500.1-UR) and incoming reactors (LR34 series).

Replacement rule: When replacing the filter, it is necessary to choose a product that matches the rated current of the prototype number. For example, for the SO84.045 model, it is usually matched with an EMC63.1-UR filter. The metal casing of the filter must be reliably overlapped with a large area of metal mounting backplate to ensure smooth discharge of high-frequency interference current. If the cable is too long, shielded cable should be used and both ends of the shielding layer should be grounded.

2. Braking Resistors

For single axis systems without regenerative power supply, braking energy is converted into thermal energy consumption through external braking resistors (such as BR-090 or BR-026 series).

Troubleshooting and replacement: If the driver reports a "Brake chopper" fault, after confirming that the internal IGBT has not broken down, the resistance of the external brake resistor needs to be measured. If the resistor breaks due to overheating (infinite resistance), it must be replaced with a resistor of the same specification. Please note that some models (such as SO84.xxx.xxxx.1xxx) have integrated braking resistors internally. It is strictly prohibited to directly connect external resistors in parallel on such models, otherwise it may cause overcurrent and burnout of the chopper.

3. Fan and heat dissipation

ServoOne's fan is a consumable part. When replacing the fan, it is necessary to turn off the power and wait for the DC bus capacitor to discharge completely (the panel indicator light goes out). When installing a new fan, be sure that the wind direction arrow must face towards the outside of the cabinet or comply with the air duct design. For modules with IP20 protection level, the fan grille cannot be removed to prevent foreign objects from entering and causing short circuits.