Page 34 - Rapid Learning in Robotics

20 The Robotics Laboratory

on an object surface, see Jockusch, Walter, and Ritter (1996).
Efficient system integration is provided by a dedicated, 64 channel sig-
nal pre-conditioning and collecting micro-computer based device, called
“MASS” (= Multi channel Analog Signal Sampler, for details see Jockusch
1996). MASS transmits the configurable set of sensor signals via a high-
speed link to its complementing system “BRAD” – the Buffered Random
Access Driver hosted in the VME-bus rack, see Fig. 2.2. BRAD writes the
time-stamped data packets into its shared memory in cyclic order. By this
means, multiple control and monitor processes can conveniently access
the most recent sensor data tuple. Furthermore, entire records of the re-
cent history of sensor signals are readily available for time series analysis.

Contact Sliding Breaking
Contact

Dynamic Sensor
Analog Signal
analog signal

Preprocessing
pulse output
Output
force sensor readout
Force Readout FSR
grip slide release
Time [s] 0 0.5 1 1.5 2 2.5 3 3.5 4

Figure 2.9: Recordings from the raw and pre-processed signal of the dynamic
slippage sensor. A flat wooden object is pressed against the sensor, and after
a short rest tangentially drawn away. By band-pass filtering the slip signal of
interest can be extracted: The middle trace clearly shows the sudden contact and
the slippage phase. The lower trace shows the force values obtained from the
second sensor.

Fig. 2.9 shows first recordings from the sensor prototype. The raw sig-
nal of the PVDF sensors (upper trace) is bandpass filtered and thresholded.
The obtained spike train (middle trace) indicates the critical, characteristic
signal shapes. The first contact with a flat wood piece induces a short sig-
nal. Together with the simultaneously recorded force information (lower
trace) the interesting phases can be discriminated.