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Maxon DC Motors Move Humanoid Robotic Hand

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article image Humanoid Robotic Hands

Maxon Motor Australia  is a major supplier of high precision DC Servo motors, brushless motors and drives for diverse applications in industrial automation, robotics, medical science, security, automotive and communications segments.  

There has been rapid progress in the development of robotic hands that replicate human movement; delicate DC motor driven grippers with fingers and thumbs are now no longer a vision but a reality.  

Significant progress in microelectronics and micromechanics means that multi-fingered miniature motor-driven hands can be produced with separately controllable fingers and joints that replicate the human hand.  

The German Aerospace Centre (DRL) has developed a new robotic hand in conjunction with the Harbin Institute of Technology (HIT). Incorporating micro and precise DC drive technology together with high-performance bus technology, this development is setting new standards for sensitive gripper hands that replicate human ones.  

Compared with its predecessor, the new DLR-HIT Hand II has five motorised fingers, each with four joints and three degrees of freedom. Four fingers are required for clasping conical parts, and a thumb is used as an outer support. The mechanical range of movement must be properly controlled and monitored to enable the hand to be used fully.

High-speed bus for controlling  

The DC motors in the DRL-HIT Hand II are fitted directly into the fingers. This means that particular attention has to be paid to the control processor’s information with positioning and operating data.  

Every finger joint is therefore fitted with a self-developed non-contacting angle sensor and a torque sensor. A high-speed bus transmits the data flow. Rapid feedback for comparing target and actual value is crucial for the functioning of the controller, particularly in precise and delicate applications.  

Speed of transfer of feedback is enabled by the internal real-time 25 Mbps high-speed bus developed especially for this application based on FGPAs (Field Programmable Gate Arrays).  

Only three leads are required for the external serial connection of hand and control processor. The actual control, a signal processor on a PCI insert card is integrated in a standard PC. A user-friendly interface means that the hand can be controlled at the PC with all sensor data displayed on the screen.  

Data display, controls and the connection between hand and processor have been designed for future use in the industrial environment.

Maxon flat motors as drives  

Each finger needs several drives that can all be controlled separately. In this instance, 15 brushless DC motors with Hall sensors were used for each hand.  

Maxon Motor’s EC 20 flat drives met several key requirements including affordability, commercial availability, high power density and compact design.  

Highlights of Maxon Motor’s Flat Drives

  • The motors, including Hall sensors create a unit that is only 10.4mm long with an outer diameter of 21.2mm
  • Each motor weighs 15g
  • They are mounted with harmonic drive gears from the HDUC 05 range, which has the same diameter
  • 3-watt motors, in a 12V or 24V version provide maximum torque of 8.04 mNm
  • Preloaded ball bearings ensure precise response behaviour of control commands, including changing the direction of rotation
  • Digital Hall sensors report the actual position to the controller accurately
  • Motors idle at 9,300 rpm

Thanks to compact drive technology with feedback and rapid data transfer per bus technology, the new DLR-HIT Hand II robotic hand can be controlled very sensitively and precisely.

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