Tactile Sensors: Advantages and Disadvantages

This page explores the benefits and drawbacks of various tactile sensor types. It details the pros and cons of these sensors.

What is a Tactile Sensor?

A tactile sensor is a sensing device that measures parameters like thermal conductivity, pressure distribution, touch, and other stimuli. Tactile sensing is often achieved using an array of discrete sensing elements.

Tactile sensors are widely used in:

• Touch screens of mobile phones
• ATM machines
• Tablets
• Interactive digital kiosks
• Robotics
• Computer hardware
• Computing devices
• Security systems

Tactile Sensor Types

The sensing elements used in tactile sensors vary. Here’s a breakdown of common types:

• Resistive: These include strain gauge and piezo-resistive sensing elements.

  • Strain gauges, made of thin film with a metal pattern, change resistance when strained.
  • Pressure on a piezo-resistive element compresses the material, altering its resistance.

• Capacitive: Mechanical deformation leads to capacitance variation between parallel conducting plates.

• Piezoelectric: These sensors measure voltage generated due to polarization under stress.

• Magnetic: They utilize the Hall effect to measure changes in flux density.

• Optical: They employ an array of infrared LEDs and photodetectors. Light intensity is proportional to the pressure magnitude.

• Ultrasonic: A piezo-electric component generates motion when voltage is applied across a crystal. An array of PZT transmitters and receivers is used. PZT devices generate ultrasonic sound waves and convert voltage to motion.

• Tunnel Effect: Used to determine surface topography.

• Conductive Rubber: Pressure-conductive rubber, along with stitched electrical wires, enables tactile sensing. These are thin and flexible, capable of covering three-dimensional objects.

Tactile sensors are broadly categorized into kinesthetic and cutaneous sensing. Kinesthetic sensing primarily detects internal forces (e.g., muscle motion), while cutaneous sensing detects external forces (similar to skin sensing). Key performance metrics include sensitivity, linearity, and dynamic range.

Advantages of Tactile Sensors

Here are the general and type-specific advantages:

• Simple construction and easy to use.
• Often require no cables or external components.
• Generally lower cost, leading to widespread use.
• Most types are sensitive.

Specific advantages by type:

• Resistive: Sensitive, low cost.
• Piezoresistive: Good sensitivity, low noise, simple electronics.
• Tunnel Effect: Sensitive, physically flexible.
• Optical: Immunity to EM interference, fast response, sensitive, physically flexible, no interconnections.
• Capacitive: Availability of commercial A/D chips, sensitive.
• Ultrasonic: Fast dynamic response, good force resolution.
• Magnetic: No mechanical hysteresis, good dynamic range, higher sensitivity, physical robustness.
• Piezoelectric: Higher bandwidth, dynamic response.
• Conductive Rubber: Physically flexible.

Disadvantages of Tactile Sensors

Here are the general and type-specific disadvantages:

• Resistive: High power consumption, lack of contact force measurement, generally detect a single contact point.
• Piezoresistive: Temperature sensitive, signal drift, hysteresis, stiff and frail, non-linear response.
• Capacitive: Cross-talk, complex electronics, hysteresis.
• Optical: Loss of light due to micro-bending, bulky, chirping, complex computations, power consumption.
• Piezoelectric: Temperature sensitive, not-so-robust electrical connection.
• Magnetic: Suffer from magnetic interference, somewhat bulky, complex computations, power consumption.
• Ultrasonic: Limited utility at low frequency, complex electronics, temperature sensitive.
• Tunnel Effect: Non-linear response.
• Conductive Rubber: Mechanical hysteresis, non-linear response.