MasterCal Pro is a laboratory level tool for ultra high precision Robotic Parameter Identification (RPI). MasterCal Pro uses the same basic technology as ARCís lower end MasterCalTM system, but is able to determine the complete link transformation matrixes for each axis. Link parameters can be expressed in a variety of formats, including homogeneous transformation matrixes and the popular Denavit Hartenberg notation. In addition to the standard link length, orientation, and offset information, the system supplies the complete link description, measuring manufacturing tolerance errors such as twist, skew, and center of rotation inaccuracies.
High accuracy parameter identification is used to transform ordinary Commercial Off The Shelf robotic manipulators into large envelope, high accuracy machine tools for precision applications:
- On-Line Gauging
- Off-Line Programming
- Lights Out Manufacturing
- Model Based Teleoperation
- Non-Destructive Evaluation (NDE)
- Ultrasonic and Eddy Current Inspection
Truly an enabling technology, MasterCal Pro is used to attain high levels of absolute accuracy throughout a robotís work envelope, opening the way for new and innovative applications for ordinary robotic manipulators.
In the past, robot technicians had to continually touch up points over the lifetime of a robot application. Whether due to gradual drift in robot parameters over time, or to catastrophic events such as a crashes, repairs, etc., robot programs are inevitably adjusted on the factory floor. Not only does this result in critical down time, but the subjective nature of robot programming and time pressure to get the system back on-line can result in disastrous quality variations that may not be discovered until much later in the manufacturing process.
By enabling a robot to position accurately without ever having been taught, part profiles can be downloaded from CAD data. Instead of relying on a representative workpiece during a manual teaching operation, the programmer can be certain that if there are errors in the operation, it is the part causing the problem, not the robot. In other applications, new motion profiles can be downloaded to the robot every part cycle. Remote, tele-operated systems will perform identically to graphic simulations developed in the laboratory. Straight lines will be straighter, and circular paths will be rounder.
Theory of Operation
Commercial robots are well known for being highly repeatable and reliable mechanisms. To program a robot for a given application, the robotís tool tip is moved to a series of Cartesian positions with a manual teach pendant. When the programmer is satisfied with the position and orientation of the tool relative to a representative workpiece, the programmer records the present location, or Ďteachesí the point. In automatic mode, the robot continually moves back to this location. How close the robot gets to the original taught point upon subsequent moves is the Repeatability specification of the robot. Most robots repeat within 0.1 millimeter.
The ability of a robot to attain a given position in Cartesian space without ever having been there before is known as Absolute Accuracy. This specification is rarely published for a commercially available robot, as these manipulators are notoriously inaccurate. While a robot controller can easily position a servo motor to the exact location every time, there is no feedback from the robotís tool tipÖ Only an expectation that if the motors are positioned at a given location, the tool tip will be where it was intended to go.
By accurately measuring the mechanical transfer function between the servo motors and the tool tip, MasterCal Pro supplies the information the robot controller needs to position the servo motors such that the tool tip is in the intended position in Cartesian space.
MasterCal Pro is a software upgrade to American Robotís MasterCalTM system. MasterCalTM must be purchased separately which allows the user to calculate the additional parameters required to ensure absolute accuracy.