Hiperface DSL Application Note 08, Design recommendation for servo motors

With the motor feedback systems of the HIPERFACE DSL® technology, digital signal processing is integrated into an environment that is exposed to strong electromagnetic interference. Thanks to appropriate verification mechanisms in the signal processing chain within both the encoder and the controller, as well as through differential signal transmission, this technology has been made robust against such influences. However, the stability and reliability of the motor feedback (MFB) system can be further increased through additional measures in the surrounding environment. In this context, the motor is only one link in the entire chain of installation, cabling, and control.

The MFB systems with HIPERFACE DSL® technology are connected via two twisted wires from the motor connector. It is important to ensure the wires are as short as possible and offer good flexibility. A short connection length reduces potential interference coupling, and flexibility allows for easy installation and helps prevent damage during connection. For motors with low to medium power ratings (<10 kW), additional shielding of this connection cable is not required. For higher-power motors, a shielded wire set from SICK is available. If needed, tests with the corresponding motors are recommended.

Due to the high frequencies present in modern power supplies with fast switching pulses, even small capacitances within the motor can create low-impedance current paths. In addition to qualitative measures to reduce stray capacitances in the motor itself, this effect can be mitigated in systems with high-frequency output voltages, for example, by using special bearing current chokes and sine filters, as well as through appropriate grounding and shielding. A key factor is the proper (low-impedance) shield connection of the motor cable at the motor connector. For long cable runs between the motor and the controller, separate grounding of the motor housing is also recommended. A corresponding connection option should be prepared.

When selecting the motor connector, it is important to ensure a reliable option for connecting the cable shield, as well as a design that is as symmetrical as possible. All shields of the motor cable can be terminated together at this point. If couplings are used in the connection between the motor/MFB system and the servo controller, the shielding of the data lines must be routed separately.

Although the input of the motor temperature sensor in the MFB system is protected against electromagnetic interference through appropriate measures, interference coupling at this point can be further reduced by optimizing the placement and routing of the motor temperature sensor. It is recommended to conduct tests with various mounting options for the motor temperature sensor.

Due to the specific conditions of each installation, grounding concepts and implementations must be individually evaluated, tested, and adapted as needed—for example, by using potential equalization lines.

When connecting the motor cable to the servo controller, it is important to ensure proper termination of the shields. The various cable sections should be routed with shielding for as long as possible. In particular, the encoder lines should remain shielded for the greatest possible length, ideally up to the contact point at the controller. Any exposed, unshielded wire ends should be kept as short as possible (<50 mm). A good spatial separation of the different connections (motor phases, brake, data) is recommended wherever reasonably feasible.