Sensors of DLR Hand II

A dext erous robot hand for teleoperation and autonomous operation needs at least a set of force and position sensors. Various other sensors add to this basic scheme.

Torque Sensors

Each joint is equipped with a conventional strain gauge based joint torque sensor.

Besides the torque sensors in each joint we designed a tiny six dimensional force torque sensor for each finger tip. The technical data of this tiny sensor are:

Size: length = 16 mm
Ø = 20 mm
Mass: 7 g
ange: Fx, Fy, Fz = 30 N
Mx, My, Mz = 150 mNm
Resolution: 12 Bit

This tiny sensor features fully integrated electronics and a digital serial interface with 6/8 lines. The sensor itself needs 6 lines, we use two additional lines to check the integrity of our flexible PCB which connects the sensor to the finger data collection system. Check here for more information about this tiny force torque sensor.

Position Sensors

Each joint is equipped with a specially designed potentiometer based on conductive plastic. The potentiometers are identical for economic reasons. A preamplifier and a Butterworth filter of third order is located directly beside the potentiometer for proper signal conditioning. The maximum distance to the corresponding A/D converter is roughly 20 mm. The potentiometers, each with an analogous filter of third order, would not be absolutely necessary, since one may calculate the joint position from the motor position, however they provide us with a more accurate information of joint position, and they can by the way eliminate the necessity of referencing the fingers after power up. In case of not using the potentiometers one would have to consider the elasticity of the transmission belt and the harmonic drive. With the potentiometer we achieve a resolution for the joint angles of 1/10 degree this means approximately 10 bits for the joint.

Speed Sensors

To increase the controllability of the actuators we appreciate speed sensors. The sensor is basically a position sensor with very high resolution, where the speed can be calculated by differentiation of the position signal. Each motor is equipped with two linear Hall effect sensors which are used for commutation of the motors as well. These sensors supply two sinusoidal signals with a phase shift of 120 degrees. The position within the magnetic cycle of the motor is calculated from these signals. By additionally counting the cycles the position can be calculated. This type of sensor gives us just a relative position of the motor and has thus to be referenced after power up.

Temperature Sensors

We use different temperature sensors for the monitoring of the motor temperatures and for temperature compensation purposes.

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