In the previous lesson, Zheng Motion Assistant shared how to read the position feedback from the BissC absolute encoder using the ZMC432-V2 controller. For details, click → Application of BissC Absolute Encoders in EtherCAT Motion Controllers.
Today, Zheng Sports Assistant will share with you how to read the position feedback from the SSI multi-turn absolute encoder using the ZMC432-V2 controller.
ZMC432-V2 Hardware Introduction
The ZMC432-V2 is a multi-axis, high-performance EtherCAT bus + pulse motion controller launched by Zheng Motion. It has communication interfaces such as EtherCAT, EtherNET, RS232, CAN and USB flash drive. The ZMC series motion controllers can be used in various occasions that require offline or online operation.
The ZMC432-V2 can support up to 32 axes of motion control, including linear interpolation, arbitrary circular interpolation, spatial circular interpolation, helical interpolation, electronic cam, electronic gear, and synchronous following.
The ZMC432-V2 motion controller includes 6-axis pulse outputs and encoder feedback inputs, with 24 general-purpose I/O ports and 12 output ports; two general-purpose DA ports; some output ports support high-speed PWM control; and EtherCAT has a refresh cycle of up to 125µs.
The ZMC432-V2 supports three programming methods: PLC, Basic, and HMI configuration. PC-based API programming supports interfaces such as C#, C++, LabVIEW, Matlab, Qt, Linux, VB.Net, and Python.
• Controller model requirements
(1) Controller model requirements: ZMC432-V2, ZMC406-V2;
(2) Firmware version requirement: Supported only after version 4.930-20190305;
(3) The ZMC432-V2 series controllers only support SSI/BISS communication through the AXIS4/5 axis interface.
▶▶▶ZMC432-V2 Hardware Interface and Wiring
The ZMC432-V2 controller's AXIS4/5-axis interface supports the SSI/BISS communication protocol and only supports 5V-powered SSI absolute encoders. Regardless of whether the SSI absolute encoder uses +5V as its power supply, the common terminal of the SSI absolute encoder must be connected to the controller's axis interface GND.
ZMC432-V2 Controller Interface Definition
AXIS 4/5 axis interface SSI/BISS pin definition diagram
Wiring diagram for controller and SSI absolute encoder
▶▶▶Introduction to SSI Absolute Encoders
1. Understanding SSI Absolute Encoders
SSI is an abbreviation for Synchronous Serial Interface, which is a digital interface protocol.
An SSI absolute encoder is a device for measuring position and angle. The SSI interface has a relatively simple working principle but boasts high reliability and accuracy, making it widely used in industrial fields.
SSI Absolute Encoder
2. SSI Communication Principle
SSI is a communication protocol used for data exchange between motion control and absolute encoders. It employs a synchronous serial interface mode and features a master-slave interface. Data is synchronously transmitted from the encoder to the controller via a clock signal or pulse provided by the controller. The encoder output can be binary or Gray code. Data transmission occurs via two lines: a data line and a clock line. Position information is converted into binary code and encoded into serial data; the clock signal controls the data transmission rate.
SSI Interface Diagram
▶▶▶Controller Program Configuration and Application
1. Controller Parameter Description
(1)ATYPE: Set the axis type. Setting it to 48 is an SSI absolute encoder, and setting it to 49 is a BISS absolute encoder.
(2) UNITS: Set the pulse equivalent. Taking an SSI absolute encoder as an example, the resolution is 16 bits, so the number of pulses in one revolution is 65535. The controller needs to refer to this parameter to set the pulse equivalent UNITS of the axis.
(3)ENCODER_BITS: Sets the absolute bit depth of the SSI/BISS encoder. Refer to the SSI absolute encoder manual for data bits.
(4) ENCODER_BITS command parameter setting instructions:
2. Program Configuration
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global CONST ENC_AxisStart = 4 'Starting axis number for local absolute encoder axis global CONST ENC_AxisNum = 2 'Number of local absolute encoder axes' Local absolute encoder axis configuration for i = 0 to ENC_AxisNum - 1 BASE(ENC_AxisStart + i) AXIS_ADDRESS=(-1<<16)+4+i 'Map absolute encoder axes 4,5 ENCODER_BITS =26 '26-bit absolute. ATYPE=48 'Next SSI absolute encoder
3. Zero point setting
(1) Generally, absolute encoders use signals to set the zero position.
(2) For other methods to set the zero position, consult the encoder manufacturer.
4. Absolute encoder position reading
After zeroing the encoder position at the zero point, set the UNITS and read the MPOS value of axis 4/5 to know the current position of the encoder. To obtain the original encoder value, read the ENCODER value of axis 4/5. The SSI absolute encoder position has a power-off retention function.
4-axis SSI absolute encoder position MPOS
Common problems with manually rotating SSI absolute encoders and capturing position curves on an oscilloscope
1. The download program prompts an error message indicating that axis 4/5 is set to atype48.
1. Check if the controller firmware version supports SSI/BISS absolute encoders. Firmware version 20190305 and later supports SSI/BISS absolute encoders. 2. If the MPOS value for axes 4/5 is missing or incorrect, check the wiring. Also check for encoder_bits parameter settings. Use the online command `?* encoder_bits` to check if this parameter is set correctly. This concludes our sharing on the application of SSI absolute encoders in EtherCAT motion controllers.
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