Advanced R&D in Robot Compensation with the Radian


Two of the most prestigious universities in the world: China’s Jiatong University and Yale were engaged in a partnership to develop leveld precision engraving machines and robots. For measurement and compensation of all the robots axes, they turned to the API Radian and Active Target. Finding the angle of each line in the robot’s movement was a particularly vexing problem for the team. But API gave them the data able to calculate the angles in seconds.

A team of research and development scientists from China’s Jiaotong University and Yale University are working together on a unique project. They are developing leveled precision engraving machines and robots, including the hardware and software necessary for them. To accomplish this, the R&D team built a 165-kilogram (363-pound) robot. But once the robot was designed, the team faced an even more vexing problem: how to compensate its movements?

The 165 kg-leveled engraving robot was designed for precision engraving work, making its calibration requirements extremely precise. The team needed to not only calibrate the moving trajectory for all axes and make compensations, but also obtain the coordinate points at the ends of every axis so they could later develop a robot control system using this data.

The team knew that calibrating such a large robot would be difficult and would require a high standard of accuracy, even more so for robots that are used for engraving. The team researched its options, and found that the services of API, with its dynamic laser trackers, could provide them with the best solution.

Measurement and Compensation of Axis

The robot designed by the research team had a very complicated structure with seven axes. The engineers would need to calibrate each axis movement and ensure they were stable.

Using the API Radian to measure and to calibrate the movement trajectory of each axis, an engineer from API first tracked the movement of the robot, by affixing a target to the robot arm and running it through its motions. The engineer was able to get the coordinate value of the points collected during that dynamic measurement at a rate of 3,000 points per second, rapid enough to easily collect enough sample points through the robot’s range.

After the data collection, the API engineer fit the points into a circle and uses the Radian’s software to find the center point of the circle. The engineer then connects the center point with each point collected with lines, and finally calculates the angle between each lines.

With these values, the engineer can compare the robot’s movement with the original program in the robot’s control system. The engineer can compare the differences and figure out adjustment values to compensate for the movement of the robot.

An Easy Rapid Perfect Solution

The team leader, Dr. Kong, said that finding the angle of each line in the machine’s movement was a problem that he and his colleagues struggled to address for a long time. The Radian not only made this calculation simple, but fast as well.

“To our total surprise, in just a few minutes, API resolved the problem. It’s really easy and fast. Perfect!” Kong said.

To determine the value of the central axis measurement, API engineers fixed two points on every axis and let the robot run through its movements. They then fit the collected points into two circles through the software. After that, they used a line to connect the two center points of the circles and used measurement software to calculate the angle of that line.

Active Target to Accelerate the Measurement

During the measurement, API engineers also used the API Active Target. Different from Unlike API’s fixed SMRs, the Active Target can lock onto a laser tracker beam and then reposition using internal motors sot that is always facing the beam and never loses contact with the tracker. The use of the Active Target dramatically improved the efficiency of the R&D team’s work.

Stable Performance in Harsh Environment

The R&D team was not only impressed with the Radian’s performance, but its ability to perform in the conditions of the laboratory as well. With several different cutting machines and engraving robots in operation, the lab was often dusty. But the Radian’s design kept dust from penetrating its internal sensors, and the instrument was able to work reliably and accurately regardless of the atmosphere around it.