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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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