There has been rapid progress in the development of robotic hands that replicate human movement; delicate grippers with fingers and thumbs are now no longer a vision but a reality. Soon multi-fingered hands will also feature in the daily work environment. Where simple but robust two or three-fingered grippers are currently employed, soon complex five-fingered hands will also be able to carry out intricate tasks.

The human hand is undoubtedly one of the most universal and complex tools of nature. The German Aerospace Centre (DRL) has developed a new robotic hand in conjunction with the Harbin Institute of Tech-nology (HIT). Compared with its predecessor, the DRL-HIT-Hand I, the new DLR-HIT Hand II has five fingers, each with four joints and three degrees of freedom and is smaller and lighter. 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.

The 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. This is the only way that the discrete drive can show all its strengths in situ. Every finger joint is therefore fitted with a self-developed non-contacting angle sensor and a torque sensor. Due to the application, both sensors must resolve very highly. A high-speed bus transmits the data flow. Rapid feedback for comparing target and actual value is crucial for the function of the controller, particularly in precise and delicate applications. Therefore, aside from the data volume, speed of transfer is also vital.

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 are used for each hand. maxon motor’s EC 20 flat drives meet several key requirements, in that they are inexpensive, commercially available products with a high power density in a compact design. The motors, including Hall sensors, create a unit that is only 10.4 mm long with an outer diameter of 21.2 mm. Each motor weighs 15 g. They are mounted with harmonic drive gears from the HDUC 05 range, which have the same diameter. The 3 watt motors are available in a 12 or 24 V version and provide maximum torque of 8.04 mNm. Good dynamic behavior and preloaded ball bearings ensure precise response behavior of control commands, including changing the direction of rotation. The digital Hall sensors always report the actual position to the controller accurately. The 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 can be controlled very sensitively and precisely. Micromechanics and microelectronics complement each other perfectly. Today, standard components can be used to produce well-designed products which would have been previously unimaginable, even with expensive special developments.