Y-Blog / The 411 on Relative Job Function

The 411 on Relative Job Function

Posted: 13/05/2019 12:19:04 p. m. by David OConnell
Topics: Programming, Tips and Tools

In a manufacturing landscape where requirements are ever-changing, a reliable and feature-rich robot controller is a valuable tool. Convenient and powerful functions that can be cross-utilized between applications are optimizing robotic workcells each day, and companies of all sizes across various industries are realizing the full value of dynamic controller functionality. From improved cycle times to reduced rework, overall productivity is being enhanced.

While developing a keen understanding of each controller function may offer a bit of a learning curve to some operators, once the knowledge to utilize these functions is gained, companies can leverage their current systems to their full potential. This is the case when applying the Relative Job Function. Often underutilized, using this function for your robotic programs can be a powerful tool for maintaining a successful and efficient robot system.

Relative Job Function
The default method of recording position data for the Yaskawa robot controller (standard job) is with a set of pulse numbers, which represent the amount of revolutions of the S, L, U, R, B and T axes. Relative jobs, on the other hand, have the position data or points represented as a set of three values (X, Y, Z). The points of a relative job are always relative to a specific coordinate system (or frame). Relative jobs can be executed in three frames:
  • Robot frame – a frame that is at the origin of the robot (S-axis and L-axis intersect).
  • Base frame – a frame that would represent a robot on some type of transporter device, thus giving the robot extended range along one of its axes.
  • User frame – a custom frame or coordinate system that can be created anywhere in the robot working space.

There are multiple uses for the Relative Job Function, making this controller option one of the most advantageous to implement. Uses for this function include:

Connecting the Virtual World to the Physical World
When a job is created in the offline environment, there needs to be a way of connecting the virtual world to the physical world. One way of doing this is by physically measuring the real-world objects and creating a virtual world to exactly match these dimensions.

While this methodology would ensure that a program created in the simulation could “drop in” to the real-world controller and actually work, it is untimely. The reality for Yaskawa Motoman as a systems integrator is that the physical world lags the virtual world by a couple months, meaning it is more ideal to start the programming process well before an actual system build begins and equipment is installed.

Utilizing the Relative Job Function allows companies to optimize robotic implementation by creating a robot job (program) tied to a user frame in a comprehensive offline programming software platform, such as MotoSim®. This way, a few months later when programming in the real world is ready to begin, all that simply needs to be done is to teach a user frame in the “real world” system that matches the user frame created in the virtual world. The robot is now able to successfully execute that job as long as it is played back in reference to the proper user frame.

Managing TCP Maintenance
Successfully managing a robotic welding system requires a solid strategy for Tool Control Point (TCP) maintenance. The first step in this process is to have some basic tools, including:

  • Welding torch alignment jig – provides a method for verifying that the physical geometry of a welding torch matches the geometry of a master or “golden torch”.
  • Standardized contact tip pointer – this is a pointer that represents the preferred wire stick out extending beyond the contact tip.
  • External pointer (point of reference) – serves as a reference point and is mounted to a fixed feature of the robotic system. This can be as simple as a stamp mark on the robot base or as sophisticated as a machined pointer mounted to a nozzle cleaning station. If an operator suspects the welding torch has been compromised in a collision, the operator can manually drive the robot to this reference point. 
For manual Tool Control Point maintenance, the operator will observe the relationship between the contact tip pointer and the external point of reference. If the alignment between these two is off more than an acceptable amount, the operator can choose to remove the welding torch and straighten it in the alignment jig.

For automatic TCP maintenance, the robot always goes to the tool sight device to verify the Tool Control Point. If the TCP is out of tolerance, the program can be formatted to automatically reteach the TCP of the welding torch. Welding programs executed after the automatic reteaching of the TCP will cause the relative job to direct the robot’s new TCP to be driven to the (X, Y, Z) values of the relative job.

Job Cloning
Relative jobs allow the same robot program to be executed in many different user frames. Imagine welding 30 or so of the same widgets onto a large part. The programmer only has to program the path for the widget one time, because that same program can be replayed over and over based on a user frame relative to the location of the widget on the larger part.

Perhaps the most popular use for the Relative Job Function, this cuts down on the amount of initial programming time required, as well as future program maintenance. For instance, if the widget changes or is redesigned, the programmer only needs to change one program, not 30.

Words of Caution
The main consideration when programming with the Relative Job Function is in training the robot how to get from one extreme point to another. Without an intermediate point between these two extreme points, the robot will go to the point in the most efficient manner. This might mean the T-axis will rotate the wrong direction. Programmers must also consider arm or torch interferences with peripheral equipment.

Overall, once the use of the Relative Job Function is mastered, it is quite beneficial to optimizing robotic operations. To develop a stronger knowledge about Yaskawa robots, consider attending a class at Yaskawa Academy. And, as always, for technical questions or assistance with your Yaskawa robot, please contact our Yaskawa Support Services experts at 937-847-3200.


David OConnell is a Senior Application Engineer at Yaskawa America Inc. – Motoman Robotics Division


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