project specification

DLR Hand II

The DLR Hand II is an anthropomorphic dexterous grasping and manipulation system. The hand consists of four identical fingers with four joints and three degrees of freedom each. The hand has an additional degree of freedom in the palm which allows the hand to adjust perfectly for either stable grasping or fine manipulation. It has complete integration of the actuation system, sensors and communication electronics in the hand which leads to maximum flexibility and allows easy interfacing to different robots. The hand's sensors allow the precise control of the hand parallel to a very sensitive feed-back of forces and finger positions. This is the prerequisite for dexterous telemanipulation.

Specifications

Length30
Width15
Depth15
Weight1.8
Degrees of freedom13 3 each finger
Payload30 N perpendicular to extended finger
Power supply24 V DC (20A)
Speed360 °/s joint velocity
Sensors
3 DMS based torque sensor each finger
3 joint position sensors each finger
3 motor position sensors each finger
multiple temperature sensors

Overview

The hand has an additional degree of freedom in the palm which allows the hand to adjust perfectly for either stable grasping or fine manipulation. It has complete integration of the actuation system, sensors and communication electronics in the hand which leads to maximum flexibility and allows easy interfacing to different robots. 

The hand's sensors allow the precise control of the hand parallel to a very sensitive feed-back of forces and finger positions. This is the prerequisite for dexterous telemanipulation. 

The human hand is the template for the design of the anthropomorphic DLR robot hand which is a universal dexterous grasping and manipulation tool for service robotics. 

The finger joints are actuated by specially designed linear actuators.  Each linear actuator consists of a combination of a brushlcss DC  motor with hollow shaft and DLR's miniaturised planetary roller spindle drive. The finger is equipped with various sensors, and any space in the finger is occupied by sensor signal processing electronics. The sensors are integrated into the mechanical structure to prevent damage. Every finger unit with its 3 active degrees of freedom integrates 28 sensors. A small separate controller box houses the finger controllers coupled by a fiber optic link ring to any external workstation running the hand controller.  

Mechanical Structure 

Each of the four identical fingers has two independent units, the base joint unit with two degrees of freedom made in a cardanic manner and the finger unit with one actuator for two joints. Two actuators fixed in the base joint unit result in a slight kinematic coupling of the two  axes. 

Sensors

The hand has strain gauge based joint torque sensors in each joint. Next to that, it has optical position sensors integrated in every joint. A separate joint angle sensor is necessary due to the presence of slippage in the planetary roller spindle drive  and hysteresis  of  tendon transmission. The sensor is based on a one-dimensional PSD (Position Sensitive Device). This PSD is illuminated by an infrared LED via an etched measurement slot. 

The hand has speed sensors to increase the controllability of the actuators. A Tracking Converter provides high resolution (3072 steps per motor revolution) position information of the motor's  rotor. The sensor is based on linear Hall effect sensors as commutation sensors in the motors. The Tracking Converter is a  hardware circuit which converts the three sinusoidal commutation signals to a high resolution position information.  

Tactile sensors cover each finger link, consisting of tactile foils detecting center and size of external forces applied to the fingers. The sensors are based on FSR (force  sensing  resistor) technology and arranged as XYZ pads. They are also suitable for low level joint control. The finger tips provide a light projection  laser diode to simplify image  processing for a tiny stereo  camera system  integrated in the hand's palm. Temperature sensors and light barriers are implemented for security purposes. The hand   is also equipped with a six dimensional force torque sensor in the wrist. 

Hand Controller Hardware Design  

The hand is controlled by a multiprocessor system based on a fully modular concept. The control architecture is split into two levels, the global hand control level and the local finger control level. The global hand controller is externally located in a PC running  a real time operating system. 

The local finger controllers are placed near the hand and attached to the  manipulator which is carrying the hand.

The hand controllers and local finger controllers communicate via SERCOS (SErial Real Time Communication System) by fiber optic link.

References

This paper gives an overview of the experiments performed with the DLR hands, the hands abilities and the things that need to be done in the future.

Christoph Borst, Max Fischer, S. Haidacher, et al. 2003

Describes the design philosophy, the open skeleton design, and kinematic design. Goes into the actuator system, sensor equipment, and integrated electronics. Describes the communication architecture, conclusion, and future work.

J Butterfa, B,M.Grebenstein, H.Liu, et al. 2001

Gives a brief description of feedback control systems engaged in DLR’s multi-sensory 4 finger robothand.

H.Liu, P.Meusel, J.Butterfass, et al. 1998

Describes the overall system, the mechanical structure, and the hardware design. Goes into the finger controller architecture and software design.

J. Butterfass, S. Knoch, G. Hirzinger, et al. 1998 (Paywall)

Wevolver 2022