Robotics Sensors and Actuators

Answer

1. What is Strain Gauge?

Resistive sensor measuring strain $\epsilon = \Delta L/L$ via resistance change. Bonded to structure, deforms with it.

2. How It Works

Resistance $R=\rho L/A$. Strained → $L$ ↑, $A$ ↓ → $R$ changes: $\Delta R/R = G_F \cdot \epsilon$, $G_F$ gauge factor (~2). Wheatstone bridge measures $\Delta R$: $V_o = V_s \cdot (\Delta R/4R)$ for quarter bridge.

3. Advantages

• High sensitivity for force/pressure/weight.
• Small, cheap, static + dynamic.
• Easy bridge interfacing.

4. Disadvantages

• Temperature drift (needs compensation).
• Small signal (mV) needs amplification.
• Bonding sensitive, hysteresis.
• Nonlinear for large strain.

5. Applications

• Load cells, weighing scales.
• Robot force sensing, torque measurement.
• Structural health monitoring.
• Pressure diaphragms.

Final Answer

Strain gauge = $\Delta R/R=G_F\epsilon$ via Wheatstone bridge; advantages high sensitivity for force, used in load cells/robot force, disadvantages temperature drift and small signal.

Answer

1. What is Ultrasonic Sensor?

Non-contact distance/proximity sensor using ultrasound (40kHz) time-of-flight.

2. How It Works

Transmitter emits chirp → reflects off object → receiver measures TOF $T$, distance $d = c\cdot T/2$, $c≈343$m/s air.

3. Types

Type	Principle
Transceiver (single)	Same element TX/RX
Separate TX/RX	Two elements
Analog	Continuous $d$ voltage
Digital	Threshold binary

4. Advantages

• Works on any material/color, transparent.
• Range 2cm–4m, low cost.
• Not affected by light.

5. Disadvantages

• Slow (sound speed), 40ms per measurement.
• Beam spread (30°), poor for narrow.
• Temperature affects $c$, soft materials absorb.
• Minimum dead zone ~2cm.

6. Applications

• Robot obstacle avoidance, parking.
• Level sensing (tank).
• Medical imaging, non-destructive testing.

Final Answer

Ultrasonic = $d=cT/2$ TOF, types transceiver/separate, advantages material-independent range, used for robot navigation and level sensing but slow and beam-wide.

Answer

1. What is Torque Sensor?

Sensor measuring twisting moment $\tau = r \times F$ (Nm) on shaft.

2. How It Works

Twist angle $\theta = TL/(GJ)$ or strain on shaft. Transduction via strain gauges at 45° (max shear) on shaft, Wheatstone bridge measures $\Delta R$.

• Reaction: Static mount measures reaction torque.
• Rotary: Slip rings/telemetry for rotating shaft.

3. Types

Type	Principle
Strain gauge	$\Delta R/R$ on shaft
Magnetoelastic	Permeability change
SAW	Frequency shift
Optical	Twist angle via encoder

4. Advantages

• Control joint effort, assembly.
• Overload protection.
• Small, high sensitivity.

5. Disadvantages

• Temperature drift, needs calibration.
• Slip ring wear for rotary.
• Cross-sensitive to bending.

6. Applications

• Robot joint torque control, grinding, screwing.
• Automotive engine, steering.
• Prosthetics.

Final Answer

Torque = strain on shaft at 45° via bridge; types strain gauge/magnetoelastic; used for robot joint control with high sensitivity but temperature drift.