How a Hybrid Plug-in Connector Ensures a Compact, Flexible, High-Performance Motor Control System
Contributed By Digi-Key's North American Editors
The use of increasingly compact motor controllers is growing across a wide range of Industry 4.0 and Industrial Internet of Things (IIoT) applications, from robotics and material handling to food and beverage. However, as the controllers shrink, it becomes challenging for designers to simply and cost-effectively route and connect both power and data signals, while ensuring electromagnetic compatibility (EMC) and operator safety.
Advanced open source interfaces such as high-performance interface digital servo link (Hiperface DSL) and single-cable solutions (SCS) open link have emerged to help connect both power data signals using a single compact connector. This simplifies connectivity but makes the quality, design, and performance of that connector critically important to ensure signal integrity, EMC, and compliance with IP20 touch-proof and ingress requirements.
This article briefly describes the Hiperface DSL and SCS open link interfaces before discussing the electrical and mechanical requirements of a connector mechanism that can carry both power and data signals in a space-constrained environment. It then introduces hybrid motor control connectors from Weidmüller and shows how they can be used to meet these requirements.
What are Hiperface DSL and SCL open link?
The move to Hiperface DSL and SCS open link is an effort to put both power and data on the same connector to save space, lower cost, and simplify the design of high-performance motor controllers (Figure 1). Both are based on RS-485.
Figure 1: Hybrid plug-in connectors for Hiperface DSL and SCS open link save space on the motor drive printed circuit (pc) board and simplify connectivity. (Image source: Weidmüller)
Hiperface DSL is a digital protocol for single cable that includes two shielded wires for bi-directional communication and encoder power, motor power cables, and motor brake cables (Figure 2).
Figure 2: A basic Hiperface DSL compatible cable consists of three elements: a power supply (three-phase power, large brown in black, and ground, brown in yellow/green), a separately shielded motor brake pair (small brown in black), and a separately shielded data pair (brown in blue and brown in gray) for digital data transfer, all in a shielded cable. (Image source: Weidmüller)
Hiperface DSL has a data transmission rate of 9.375 megabaud (MBaud) over cable lengths up to 100 meters (m) between the motor controller and the motor. There are two ways to transmit data on Hiperface DSL; cyclically, as fast as possible given signal and noise conditions, or synchronously with the controller clock. The Hiperface DSL protocol includes several important features:
- The ability to synchronously process position and rotation speed information from the encoder with cycle times as short as 12.1 microseconds (μs).
- A maximum cycle time of 192 μs for the transmission of the safe position of the motor feedback system.
- Meets the Safety Integrity Level (SIL) 2 requirements of IEC 61508 for the redundant transmission of the safe position of the motor feedback system with a maximum cycle time of 192 μs.
- Meets the SIL 3 requirements of IEC 61508 when used in suitable motor feedback systems.
- Bi-directional general data transfer with a bandwidth up to 340 kilobaud (kBaud) for the transmission of parameters, including storage of an electronic type label of motor controller data and an electronic type label for the motor feedback system.
- A separate channel carrying data from external motor sensors (acceleration, torque, temperature, and so on), connected to the motor feedback network by the Hiperface DSL Sensor Hub protocol.
The SCS open link motor feedback interface is also designed to support bidirectional data between a motor and controller, including encoder data at rates up to 10 MBaud. It supports two and four-wire implementations. SCS open link is optimized for Industry 4.0, especially with respect to emerging IIoT applications, such as motor condition monitoring and predictive maintenance.
Like Hiperface DSL, SCS open link is certified up to SIL 3. In addition, SCS open link meets the functional safety requirements of EN ISO 13849 performance level e (PLe), Category 3. These single-cable solutions satisfy the functional safety requirements of IEC 61508-2: 2010 and IEC 61784-3: 2017.
The connector challenge facing Hiperface DSL and SCS open link
For Hiperface DSL and SCS open link to operate reliably, a well-shielded connection is needed between a motor with an encoder and the drive. The use of plug-in connectors and connection terminals to minimize the number of interfaces helps. Having continuous, shielded cables between the motor and encoder and the drive is also necessary. A single shielded cable with two plug-in connectors, one optimized for connection to the motor and one optimized for connection to the drive, provides an economical approach and is implemented in both Hyperface DSL and SCS open link.
In addition to the use of a shielded cable, the shielding needs to be properly terminated on both ends of the cable. Plug-in circular connectors (usually M23 circular connectors) with a metal housing are used on the motor side of the interconnect (Figure 3).
Figure 3: Cable lengths up to 100 m between motor and drive are supported by both Hiperface DSL and SCS open link; the motor connection is on the left, the hybrid plug-in connector for the motor controller is on the right. (Image source: Weidmüller)
To control costs, the plug-in connector on the drive side of the interconnect does not need to have metal housing. The physical design of drive connectors is non-standardized, so drive designers need to be careful when developing their own connector in order to meet performance requirements, while readily connecting to printed circuit boards to simplify connections and minimize connector costs. With proper cable design and assembly, and good EMI shielding practices, cable lengths up to 100 m are achievable.
Three-in-one connector solutions for power, signals, and EMC
Though it’s possible to spend time developing a connector design, few motor drive designers have the experience or time required to become versed in the nuances of connector design, despite requiring the best performance possible. Instead, they can turn to companies such as Weidmüller that have already focused on the issues and come up with some elegant solutions.
For example, its OMNIMATE Power Hybrid connectors are a three-in-one solution that includes signal, power, and EMC features to implement both the Hiperface DSL and SCS open link protocols while saving space on the motor drive pc board as well as in the control cabinet. The connectors are available in several configurations including six-positions (Figure 4, left), seven-positions, eight-positions, and nine-positions (Figure 4, right).
Figure 4: The OMNIMATE Power Hybrid connectors are a three-in-one (power, signals, EMC) solution with a self-locking middle flange (red). They come with six (left), seven, eight, or nine (right) positions. (Image source: Weidmüller)
These hybrid connectors include power and signal contacts with push-in wire connections on a 7.62 millimeter (mm) pitch, and meet the requirements of IEC 61800-5-1 and UL 1059 Class C 600 volts (for the power contacts).
The connectors feature several practical design features needed to ensure reliable connections. First, they have good separation between the encoder and motor power connections to minimize EMC concerns. Second, the arrangement of the various signal and power connections has been given careful consideration. For example, “neutral” connections such as the protective earth (PE) ground are in the middle, and signal and data connections for the encoder lines and the motor brake lines have been symmetrically and laterally placed.
For ease of use, the one-handed, tool-free, self-locking, plug-in interlock mechanism reduces installation and maintenance times. The interlock also reduces the space requirements by one pitch width, compared with other solutions. The 30˚ cable entry angle on the shield saves up to 10 centimeters (cm) between rows, reducing solution size.
Using the OMNIMATE Power Hybrid connector effectively
To take full advantage of the OMNIMATE Power Hybrid connectors, correct cable assembly practices and shielding terminations are necessary to control EMI and ensure system reliability. Though thoughtfully designed, the OMNIMATE Power Hybrid is still a single-cable interface, so the power and signal lines are still in relatively close proximity. As such, good design practice requires ensuring a low-impedance connection between the cable shielding and the connector. The OMNIMATE’s inclusion of a shielding connector plate with a pluggable spring contact is especially helpful here. This provides a vibration-proof shield connection to the drive and enables a solid connection of the shielding braids for the power and encoder cables (Figure 5). Having the largest possible contacting surface for the shielding connections provides an optimal solution.
Figure 5: Example of a low-impedance shielding connection between a single cable and a plug-in hybrid connector solution using one metal cable tie. (Image source: Weidmüller)
There are several attachment options for connecting the outer and inner shields to the shield connecting plate. These options include various combinations of metal cable ties and hose clips that are arranged to ensure that the attachment is secure and takes place as close as possible to the signal connections (Figure 6).
Figure 6: There are a variety of ways to connect the cable shielding to the OMNIMATE Hybrid Power connector, including the use of metal cable ties and hose clips. (Image source: Weidmüller)
The spring-loaded mechanical design provides designers of motor controllers with maximum freedom to place the shielding connection on a heatsink or directly on the pc board, ensuring a reliable and vibration-proof surface contact area.
Performance testing and safety
Once a design is completed and a cable assembly is produced, it is important to measure the effectiveness of the cable shield. For example, the KS04B measurement from VG95373-41, "Electromagnetic compatibility of devices – methods for measuring shielded cable and shielded protective cable hoses", is useful to determine the impact of the contacting points on the shielding braid and the sockets and plugs, and the quality of the shield itself. The measurement method is limited, but it is useful for comparing and evaluating the effectiveness of different shields and shield-contacting approaches (Figure 7). Limitations of the KS 04 B measurement include a standardized cable length of only 1 m and the use of a 50 ohm (Ω) system that does not consider the actual cable impedance.
These plug-in connectors meet IP20 safety standards and are touch-safe for operators when wired correctly. However, there are large-value capacitors in a typical motor controller that can shock operators if not properly managed. It is essential that the capacitors have been discharged and no voltage is present when maintenance is being performed. Though IP20 rated, it is still recommended that operators wait several minutes for the capacitors to discharge before touching the connectors, providing another level of safety. Finally, the open design of these hybrid connectors allows operators to instantly see and verify that all cables are undamaged and connected correctly.
The shift to a single, hybrid interconnect system to carry both power and data in compact, high-performance motor controllers makes it difficult for designers to support EMC and ensure reliable operation, while also ensuring operator safety. However, as shown, there are well-designed three-in-one hybrid plug-in connector solutions that support protocols such as Hiperface DSL and SCS open link for power and data, while also providing reliable EMC shielding and meeting IP20 safety standards.
Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.