Hollow shaft gear increases robot payloads

An innovative hollow shaft gear system has helped Reis Robotics to make significant weight reductions to the operating arm of its latest six-axis, CO2 laser robot.

An innovative hollow shaft Harmonic Drive gear system, developed and manufactured by Harmonic Drive, has helped Reis Robotics to make significant weight reductions to the operating arm of its latest six-axis, CO2 laser robot, which has been developed for use in the automotive sector for precision cutting of plastics and fibre reinforced plastic components.

In addition, the Harmonic Drive system has enabled Reis Robotics to increase the payload of the robot, without adversely affecting the working envelope of the system or the applied power of the laser.

Reis Robotics is one of the world's leading developers and integrators of robotics systems for use in a wide range of industrial applications.

In particular, the company's RV6L vertical articulated arm robot offers a flexible, high power solution for materials processing, and incorporates state of the art CO2 laser technology.

The laser beam on the RV6L is directed from the source to the cutting head by a sequence of enclosed optical quality lenses and mirrors, or beam guides, mounted within the articulated upper arm of the robot itself.

To enable the upper robot arm to carry a heavier payload than would otherwise be possible, of up to 400kg, the relatively heavy laser source used in the RV6L is located on the lower robot arm, near the base mounting plate.

This configuration, however, means that the laser beam has to be focussed through the articulated connection joint between the lower and upper robot arms.

The articulated joint is crucial as it effectively allows the robot system to move through the third, fourth and fifth rotational axes.

In a conventional system with the laser source mounted on the upper arm, this joint would normally be formed from a solid construction containing the mechanical gears, bearings and connections needed to enable the arms to coordinate and move quickly and accurately; in the RV6L, such a construction would have required the use of extra beam guides or meant that laser source would have to be repositioned, thereby reducing the payload capability of the robot.

To overcome these problems Reis Robotics used a unique solution, designed and manufactured by Harmonic Drive, that enabled the laser source to be located on the lower arm, increasing the payload of the upper arm and also allowing the number of beam guides to be reduced from six to just four.

Harmonic Drive is based in Germany and the UK, and specialises in the development of high performance precision gears, actuators and motion control systems.

The company's innovative HFUS Harmonic Drive technology is based on a simple three part assembly, with an integrated Wave Generator, Flexspline and Circular Spline being combined to form an extremely robust gear component set.

This offers exceptional positioning accuracy, to within one second of arc, with repeatability of just a few seconds of arc, plus a high torque capacity and torsional stiffness, zero backlash and a low weight and small size.

For Reis Robotics the main advantage of the HFUS Harmonic Drive system was the unique ability of the gear component set to be supplied with a large diameter hollow central shaft through which the laser beam could be directed.

This is possible as the HFUS component set features a special Flexspline diaphragm, which opens outwards, rather than inwards, and is supplied as a complete unit with housing and output flanges, plus cross roller output bearings between the Circular Spline and the housing flange to support the upper robot arm.

The solution developed by Harmonic Drive has played an important role in helping to enhance the performance and functionality of the latest RV6L laser robot, enabling Reis Robotics to offer its customers an advanced, efficient and reliable system that meets the needs of a wide range of applications.

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