Thomson Electrac HD Linear Actuator Motion Control per CAN Bus

By Wilfried Voss

This application note focusses on the Thomson Electrac HD series of linear actuators. They support two higher-layer protocols based on Controller Area Network (CAN): CANopen, and SAE J1939. You can control the actuators merely with hardware switches (Start, Stop, Forward Motion, Backward Motion), but, in addition, both CAN protocols allow to regulate the linear speed.

If your application requires mere motion control (Start, Stop, Forward Motion, Backward Motion, Speed Control), you are better off with SAE J1939 because you don’t need to install the protocol stack. The Electrac actuator supports some SAE J1939 protocol features (e.g., the address claim procedure), but you can ignore the protocol requirements and control the linear motion with mere CAN Bus data frames (using a 29-Bit message identifier). Thus, “CAN Bus communication” describes the operation mode more accurately.

The CAN/J1939 approach will shorten the development cycle tremendously, which is why the focus is on SAE J1939 and not CANopen.

In view of various undocumented eccentricities, you should not start programming the Electrac per CAN/J1939 without reading this document. The Electrac user manual was primarily created for installation, while this application note provides a valuable source for programmers.

• Language: English
• Publisher: Lulu.com
• Release date: Mar 1, 2023
• ISBN: 9781312847682

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Table of Contents

Table of Contents

Introduction

Before You Start That Development…

The Scope of this Application Note

The Thomson Electrac HD Linear Actuator

What is a Linear Actuator?

Download the User Manual

A Brief Introduction to CAN Bus and SAE J1939

Controller Area Network

SAE J1939

Controlling the Thomson Actuator

Manual Control

Software Control

Node Address Configuration

Sleep Mode

Actuator Control Message (ACM)

Actuator Feedback Message (AFM)

Safety Considerations

Testing Approach

Programming Hardware & Software

Arduino Due & Arduino IDE

Dual CAN Bus Interface

Control Connections

CAN Bus Connection

ARD1939 – SAE J1939 Protocol Stack for Arduino

CAN Bus & SAE J1939 Communication Protocol

Designing the ACM

Interpreting the AFM

Example Programs – Basic & Extended

Basic Version

Extended Version

Download Links

Hardware Connections & Programming Notes

General Aspects

Timer Control

Reading an Analog Signal from a Potentiometer

Reading Digital Signals (Switches, Pushbuttons)

Building the Actuator Control Message (ACM)

Handling the Actuator Feedback Message (AFM)

The Startup Sequence

Checking the CAN Bus Connection

Managing the Threshold Speed

Checking Motion End

Thomson Actuator – Oddities

CAN Bus Termination

Fatal Error Flag at Low Speed

Overload Flag at Power-Up

Multiple Actuators in the Same Network

Introduction

As part of a customer project, I was asked to develop a hardware system to control a linear actuator, specifically the Thomson Electrac HD model with SAE J1939 interface. The Electrac series of actuators supports two higher-layer protocols (HLP) based on Controller Area Network (CAN): CANopen, and SAE J1939. CANopen is suited for industrial automation, while SAE J1939 was designed for diesel engines (trucks, trains, ships, tanks, tractors, and more). You can control the actuators merely with hardware switches (Start, Stop, Forward Motion, Backward Motion), but, in addition, both CAN protocols allow to regulate the linear speed.

At first glance, CANopen appears to be more suitable for controlling a linear actuator in industrial applications, but that is only true when you are already involved with CANopen, i.e., you know how to implement a CANopen protocol stack (which is not a small feat).

However, if your application requires mere motion control (Start, Stop, Forward Motion, Backward Motion, Speed Control), you are better off with SAE J1939 because you don’t need to install the protocol stack. The Electrac actuator supports some SAE J1939 protocol features (e.g., the address claim procedure), but you can ignore the protocol requirements and control the linear motion with mere CAN Bus data frames (using a 29-Bit message identifier). Thus, CAN Bus communication describes the operation mode more accurately.

The CAN/J1939 approach will shorten the development cycle tremendously, which is why I focus on SAE J1939 in this application note and not CANopen.

Initially, I had published a brief post on our website, titled Thomson Electrak Linear Actuator with SAE J1939 Interface for Railway and Industrial Applications to share some general insights. However, since then, I have been asked by various engineers from all over the world to share the hardware design and the Arduino source code.

It appears there is a demand for extended support, especially since the Electrac’s user manual leaves ample room for interpretation and lacks application examples. Consequently, my application turned into a major research project, which also explains the previously mentioned calls for help.

Don’t get me wrong, the Electrac Linear Actuator is a great product, and it is always rewarding to see the application literally move. Yet, working on this application was at times frustrating. After months of working with this product (time frame, not efforts), I still discovered what I call undocumented oddities (See chapter Thomson Actuator – Oddities).

Unfortunately, the support from Thomson I received was at best mediocre. I’ll leave it at that. In view of various undocumented eccentricities, you should not start programming the Electrac per CAN/J1939 without reading this document. The Electrac user manual was primarily created for installation, while this application note provides a valuable source for programmers.

The detected, yet undocumented idiosyncrasies caused profound delays during the development process. When you discover an odd