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Compact rotary encoders help raise tool grinding productivity through automation

Swiss company Strausak AG, which manufactures CNC grinding machines for manufacturing and resharpening solid carbide tools, wanted to offer customers the option to automate loading and unloading of workpieces into and out of the spindle that rotates the workpiece in its U-Grind series machines. The problem was that, to achieve high tool accuracy, an HSK 50 hydraulic expansion chuck with a diameter tolerance of only a few hundredths of a millimetre has to be employed, rather than a conventional collet with automation-friendly open tolerances.

To position the carbide blank or tool to the required level of precision, Strausak turned to robot manufacturer Stäubli, which now supplies the automation solution based on a compact, 6-axis, industrial robot. The position of each CNC rotary axis is controlled by a HEIDENHAIN EQI 1100 absolute inductive rotary encoder with 18-bit resolution. The reliability of the positional data they feed back to the NUM control on the U-Grind allows the robot gripper to manipulate the workpiece to within 50 microns.

Strausak’s managing director Alexandre Condrau commented, “Removing a tool or blank from a tightly loaded pallet, transferring it to the hydraulic chuck, inserting it in an exactly horizontal movement, then subsequently carrying out the reverse motions, are highly complex manoeuvres that involve simultaneous interpolation of all six robot axes to attain the required accuracy and repeatability.

“Additionally, we wanted to accomplish this in a compact space so that access to the working area is not restricted by the robot arm and the operator’s view of the grinding process is not obstructed.

“We were happy that Stäubli partners with HEIDENHAIN for its rotary encoder requirements, as the compact dimensions of its inductive products ideally suit our application. We also have CNC positioning of the swivelling grinding wheel head on our machines and to achieve the necessary precision we use a HEIDENHAIN ERA 4000 incremental angle encoder.”

Many carbide tools have complex geometry and the programs that run on U-Grind machines are usually long; a small series of five special tools may typically take several hours to produce. Thus with the introduction of reliable, automated workpiece handling using the pick-and-place robot, Strausak offers its users the possibility of a significant competitive advantage through redeployment of labour and the possibility of ghost shift operation.

Strausak sees further development possibilities that could help its customers even more. The company is currently working on programming the robot to regrip the workpiece and readjust its insertion distance in the hydraulic chuck to enable machining of very long tools. Other functionality being investigated is using the robot to exchange toolholders as well, so that cutters of different diameters may be produced without manual intervention.