The objective will be achieved by mastering all the error origins singularly to finally combine them in a global dynamic compensation.
The following steps have to be accomplished:
- Development of an adequate measuring system, that includes:
- Measure of translations and rotations at high-precision.
- Measure of all the temperatures involved in the measuring loop.
- Development of a contactless force simulator, to simulate manufacturing process forces on the end-effector.
- Considering the thermal drift, calibration of a 1 DOF linear axis.
- Considering thermal and manufacturing forces drift, calibration of a 3 DOFs parallel kinematic delta robot (Agietron Micro-nano).
- Considering thermal and manufacturing forces drift, calibration of a hybrid system composed of two 3 DOFs robots (Agietron Micro-nano and MinAngle).
- Calibration confirmation of the previous system by mean of indentation.
|Parallelogram used in step 2.||Agietron micro-nano, used during step 3.|
|The robot MinAngle.||Agietron micro-nano and MinAngle, step4|
The measuring system
The temperatures of all the parts in the measuring loop are acquired using a total of 12 sensors: 10 pt1000 are used for parts of the measuring loop while 2 pt100 are used to measure the air temperature.
The measure of translations and rotations is strictly linked with the temperatures reading. For us is very important to divide the robot drift by the drift of the overall system. This has been achieved using special materials with an extremely low dilatation coefficient for the static components (like invar or zerodur) and by stabilizing actively all the supports in aluminum. Also the drift due to the air temperature drift is compensated electronically.
The force simulator is in phase of development and it will be ready by the end of 2008. This system is composed of 3 inductances, which are used to create a magnetic force on the robot end-effector. Such force has been dimensioned to be as much similar to the forces emitted during a standard EDM process.
Thanks to this work it has been proved that the thermal calibration procedure is effective. The results are in the expected order of magnitude and are encouraging to continue on a more complex case.
After this phase, the measuring system will be adapted to calibrate the robot MinAngle. This robot has been specially developed to work with the previously mentioned 3 DOFs robot. The aim of this part is to see how is it possible to mix two calibration processes: it will be proposed a strategy to unify two different calibration dataset, beyond a strategy to unify two different references.
Finally a calibration confirmation will be performed. The goal of this part is to confirm all the strategy by manufacturing a special piece and by measuring it. For this task, we propose the indentation process: a diamond will be mounted on the end-effector of the Agietron Micro-nano robot, while a substrate will be mounted on the robot MinAngle. Indents will be produced in the substrate at well-known distances. Thus, the indents distances will be measured with an electronic microscope. This validation will quantify the real precision of the two robots system in an industrial environment.