Swiss company Strausak AG, which makes CNC grinding machines for manufacturing and re-sharpening solid-carbide tools, wanted to offer customers the option of automating the loading and unloading of workpieces into and out of its U-Grind machines.
However, to achieve the necessary high level of tool accuracy, an HSK 50 hydraulic expansion chuck with a diameter tolerance of only a few hundredths of a mm has to be used, 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.
The latter now supplies the required automation solution based on a compact six-axis industrial robot, on which the position of each CNC rotary axis is controlled by a Heidenhain EQI 1100 absolute inductive rotary encoder offering an 18-bit resolution (
www.heidenhaingb.com).
The reliability of the positional data that these encoders feed back to the NUM control on the U-Grind allows the robot gripper to manipulate the workpiece to within 50µm.
Strausak’s managing director, Alexandre Condrau, said: “Removing a tool or blank from a tightly loaded pallet, transferring it to the hydraulic chuck and inserting it with a precise horizontal movement — and subsequently carrying out the reverse motions — are highly complex manoeuvres that involve the simultaneous interpolation of all six robot axes to extremely high levels of accuracy and repeatability.
"Furthermore, 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 also use Heidenhain ERA 4000 incremental angle encoders for this application.”