If your machine has to coordinate multiple linear or rotary axes to move a load, it's critical to precisely synchronize the position and velocity of each axis. Positioning errors between two axes can reduce efficiency or even shut down the entire system.

Cross-coupling is an axis coordination method that allows you to maintain synchronous velocities and positions between axes with a centralized controller and distributed control system. This method provides the precise and efficient positioning required for many motion control applications.

Here's how cross-coupling ensures synchronous position, time and velocity:

Position. The central controller directly monitors feedback from both axes and generates a correction signal. For example, in a two-axis linear gantry, it reads the positioning differences between the two axes and sends a correction command to each axis's summing junction. This process eliminates the positioning errors between the two axes that could mechanically bind the system. The distributed control system is what sends the commanded position to each axis and simultaneously executes it in separate drives.

Copley Dual Axis Gantry .png

Time. In addition to position, it is necessary to synchronize the time between two motors, requiring a precise master clock. Copley drives offer excellent master clock performance because they are typically more accurate than a PC clock. One method to confirm time synchronization is to use an oscilloscope to monitor the U output of both drives. Time is synchronous if there is no edge transition drift.

Our drives also offer another advantage: position is closed at a loop update rate of 250 microseconds (μs). The update rate ensures that even if the the time between PVT points is greater, the drive interpolates the commanded position every 250 μs and executes it in synchronous time with some jitter. CANopen time jitter is ± 1 μs, and EtherCAT time jitter is ± 20 nanoseconds (ns).

Pwm Chart Image.png

Velocity. Similar to position synchronization, you can achieve cross-coupling velocity correction by measuring each motor's velocity and applying correction signals to each axis. This method speeds up one and slows down the other. CANopen masters can implement this strategy.

The Benefit of Dual Axis Drives

Dual axis drives are excellent for cross-coupling because they use a single processor that ensures both axes are controlled by the same master clock. And, because there is no network message latency, correction signals are executed at the position loop update rate in real time. Our Xenus Plus, Accelnet Plus and Stepnet Plus drives offer dual axis support.

Copley Controls Dual Drive Cross Coupling.png Copley dual axis drive performing cross-coupling.

Software Tools Simplify Cross-Coupling

The Copley Motion Library (CML), Copley Motion Objects (CMO) and CME2 are software tools that support cross-coupling.

The CML is a C++ object-oriented library that simplifies CANopen and EtherCAT program development. Not only does the CML allow low-level access to CANopen and EtherCAT networks, it also provides high-level methods to easily develop network-based motion control applications. Download the CML on our downloads page.

The CMO simplifies development for Windows-based software that controls Copley amplifiers over a CANopen network. As an API, the CMO gives programmers access to an amplifier's CANopen functions without requiring an understanding of underlying network protocol. And, CMO is compatible with client code that supports .NET assemblies. Go to our downloads page to download the CMO software.

When using the CMO and CML for cross-coupling, a linkage command links the axes, performs s-curve motion and commands straight, synchronous linear movement.

CME2 is a powerful and intuitive configuration software with a cross-coupling function. You can find the cross-coupling button on the P-Loop screen. Using the software, you can input the distance, velocity and acceleration of the desired, synchronous commanded movements and generate the trajectories. The CME2 also features an oscilloscope that lets you monitor each axis's velocity profile and check for errors. You can download CME2 on our software page.

Contact us to learn more.

Technology Blog

Optimize Multi-Axis Machine Performance With Cross-Coupling

Similar Posts

Easily Develop Deterministic Robotics Applications With Copley Motion Library

Block your calendar for Robotics Summit 2025!

What is a Servo Drive?