Page 424 - The Mechatronics Handbook

0066_frame_C19 Page 46 Wednesday, January 9, 2002 5:17 PM

Tactile Sensor Requirements
Significant advances in tactile sensing are taking place in the robotics area. Applications include automated
inspection of surface profiles, material handling or parts transfer, parts assembly, and parts identification
and gaging in manufacturing applications and fine-manipulation tasks. Some of these applications may
need only simple touch (force–torque) sensing if the parts being grasped are properly oriented and if
adequate information about the process is already available.
Naturally, the main design objective for tactile sensing devices has been to mimic the capabilities of
human fingers [9]. Typical specifications for an industrial tactile sensor include:
1. Spatial resolution of about 2 mm
2. Force resolution (sensitivity) of about 2 g
3. Maximum touch force of about 1 kg
4. Low response time of 5 ms
5. Low hysteresis
6. Durability under extremely difficult working conditions
7. Insensitivity to change in environmental conditions (temperature, dust, humidity, vibration, etc.)
8. Ability to monitor slip
Tactile Array Sensor
Tactile array sensors (Fig. 19.42) consist of a regular pattern of sensing elements to measure the distri-
bution of pressure across the fingertip of a robot. The 8 × 8 array of elements at 2 mm spacing in each
direction provides 64 force sensitive elements. Table 19.2 outlines some of the characteristics of early
tactile array sensors. The sensor is composed of two crossed layers of copper strips separated by strips
of thin silicone rubber. The sensor forms a thin, compliant layer that can be easily attached to a variety
of fingertip shapes and sizes. The entire array is sampled by computer.

TABLE 19.2 Summary of Some of the Characteristics
of Early Tactile Array Sensors
Size of Array
Device Parameter (4 × 4) (8 × 8) (16 × 16)

Cell spacing (mm) 4.00 2.00 1.00
Zero-pressure capacitance (fF) 6.48 1.62 0.40
Rupture force (N) 18.90 1.88 0.19
Max. linear capacitance (fF) 4.80 1.20 0.30
Max. output voltage (V) 1.20 0.60 0.30
Max. resolution (bit) 9.00 8.00 8.00
Readout (access) time (µs) — <20 —
©IEEE 1985.

Array processor
Sensors Preprocessor
Input Output
(Measurand)
(Vector)
µP

FIGURE 19.42 Tactile array sensor.

©2002 CRC Press LLC