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Biomechatronic Systems

Mehdi Delrobaei

Winter 2020

Unit 3: Sensors and Actuators

Sensors in Biomechatronics

• Mechatronic Sensors: Any

electrical/electronics/electro-mechanical device that converts physical quantities (such as pressure and temperature) to electrical signals (either analogue or digital).

• Bio-sensors: Any device that converts a biological response to an electrical signal. Advanced biosensors are enzyme-based, tissue-based, immunosensors, DNA biosensors, and thermal and piezoelectric biosensors.

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Types of Mechatronic Sensors

Sensors: Introduction

Environment Smart Device Environment

• Switches • Resistive • Magnetic

• Optical/Laser/Infrared

• Ultrasound/RFID

• Capacitive/Inductive

• Chemical • Others:

- Vision - MEMS - GPS

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Switches

Sensors: Switches

Smart Device

• The simplest type of sensors • Pushbutton, slide, toggle, rotary,

Hall, lever, DIP, micro, … • Objectives: enable power, sense a

contact, sense limit of travel, and human interface.

Source: Google Images 4

Switch Interface

Sensors: Switches

Smart Device

• The interfacing converts a switch action into a digital logic low/high (Digital Input).

• Interfacing to mechanical switches requires a “debouncing” hardware.

• Debouncing a switch in software is also very common.

Source: labbookpages.co.uk 5

Resistive Sensors

Sensors: Resistive

Smart Device Environment

• A variable resistor, sensitive to a physical phenomenon.

• Types: potentiometer, thermistor, photo-cell, strain gage, and flex sensors.

6 Source: Google Images

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Resistors Interfacing

Sensors: Resistive

Environment Smart Device Environment

Simple interface

Potentiometer as a position sensor

Strain gage interface 7 Source: Google Images

Linear Variable Differential Transformers (LVDT)

Sensors: Resistive

Environment Environment

Simple interface

8 Source: honeywell.com

Hall-Effect (Magnetic)

Sensors: Resistive

Environment Environment

9 Source: electronicshub.org electronics-tutorials.ws

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Optical Encoders

Optical Encoder

Environment

• One of the most precise position sensors. • Output pulses proportional to the angle of rotation.

Source: Google Images

Output of the photo-switch

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Encoders

Optical Encoder Source: Wearable Robots 11

Quadrature Encoders

Optical Encoder Source: creative-robotics.com dynapar.com

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Comparison of Position Sensors

Optical Encoder Source: Wearable Robots

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Infrared Sensors

Reflective Sensors

Environment Smart Device Environment

• Distance and motion sensors using infrared beam.

• IR rangefinders calculate the sensor-object distance through the process of triangulation.

Source: Google Images 14

Laser Rangefinders

Reflective Sensors

Environment Smart Device

• Long distance measurement; • Use a laser beam to determine

the distance and operates on the time of flight principle.

Source: Google Images

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Ultrasonic Rangefinders

Ultrasonic Sensors

Environment Smart Device Environment

• To detect obstacles by utilizing the propagation of high-frequency sound waves.

Source: Google Images 16

Radio-Frequency Sensors

Reflective Sensors

Environment Smart Device Environment

Source: Google Images 17

• To use radio-waves to detect digital data encoded in RFID tags.

Inductive Sensors

Reflective Sensors

Environment Smart Device Environment

• An inductive proximity sensor detects metal objects, with no need to a physical contact.

• A high-frequency magnetic field is generated by an oscillation circuit. If a metal object approaches the field, the induction current flow causes a load on the oscillation. The sensor detects this change and outputs a detection signal.

18 Source: machinedesign.com/

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Capacitive Sensors

Reflective Sensors

Environment Smart Device Environment

Source: Google Images

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MEMS Sensors

Reflective Sensors

Environment Smart Device Environment

• Accelerometer • Gyroscope • Magnetometer • Pressure sensors

Source: Google Images

IMU

Smart Contact Lens (Pressure Sensor)

Pressure Wire

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MEMS Sensors: Accelerometer

Reflective Sensors

Environment Smart Device

21 Source: instrumentationtoday.com

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Other Sensors (Imaging)

Reflective Sensors

Environment

Source: Google Images

MRI and fMRI

PET Scan

CT Scan

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Electrical Actuators

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Types of Electrical Actuators

• Solenoids

• DC Motors

– PMDS

– Servo motors

– Stepper Motors

– BLDC

– Vibrating Motors

• Linear Actuators

• Shape Memory Material

• Artificial Muscles

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Solenoids

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DC Motors

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Types of Gear Boxes

(Planetary)

(Spur)

(Harmonic Drive)

(Worm – Helical)

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Servo Motors

Servo Motor

1- DC Motor 2- Gear Head 3- Potentiometer 4- Control Circuit

Source: www.micromo.com/ 28

Stepper Motors

Stepper Motor Source: Google Image 29

Brushless DC Motors

• A synchronous electric motor powered by DC power and electronically commutated.

• Advantages: • Better speed versus torque

characteristics

• High dynamic response

• High efficiency

• Long operating life due to a lack of electrical and friction losses

• Noiseless operation

• Higher speed ranges

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Vibrating Actuators

• Tactile stimuli for navigation • Haptic feedbacks • Vibratory analgesia

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Linear Actuators

Linear Actuator Source: Google Image

Lead Screw

Ball Screw

Belt Drive

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Linear Actuators: Voice Coil

Linear Actuator Source: Google Image

• Voice coil actuators are direct drive mechanisms that provide precise positioning. The mechanism simply comprises a permanent magnet core and a coil winding. If a current is applied to the coil, a force would be generated.

• Medical applications: middle ear implantable hearing device, power ventricular assist device

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Linear Actuators: Piezoelectric and Pneumatic

Linear Actuator Source: Google Image

Bellow Actuator (Pneumatic) • Piezo materials expand or contract when an electrical voltage is applied, generating motion and force.

• Piezo actuators use this motion to provide very short strokes with high frequency and fast response.

Piezoelectric Actuator

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Shape Memory Material

Shape-Memory Alloy (SMA,

also smart metal, memory metal, muscle wire)

Alloys: nickel-titanium (NiTi), copper-aluminium-nickel, and, zinc-copper-gold-iron

Shape-memory polymer (SMP)

Magnetic shape-memory alloy

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Shape Memory Material: Active Endoscope

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Artificial Muscles

Carbone-Nanotube Artificial Muscle

Pneumatic Artificial Muscle

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