Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual...

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Lecture 19 Lecture 19 Dimitar Stefanov

Transcript of Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual...

Page 1: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Lecture 19Lecture 19

Dimitar Stefanov

Page 2: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Powered Wheelchairs

•1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors and automobile battery

Prescription of the type of the wheelchair depends on the user’s mobility.

In some cases – manual wheelchair for indoor and sort-distances and a powered wheelchair for long distances.

Page 3: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Powered wheelchair with combination of other devices – communication devices, computer access devices, respirators, and reclining seating systems.

NEMO, Madentec Limited, http://www.madenta.com/

54 commands

HMI by voice, switch, joystick, wheelchair controls.

Page 4: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Depending on their construction:1. Power bases2. Power wheelchairs3. Scooters.

Four classes wheelchairs (depending on their power):Class 1 – carry up to 100 kg, maximal speed of 1.1 to 1.8 ms-1 , capable to carry up to 6° slope, travel over than 10 km on a single charge, climb a 25 mm obstacle, for indoor use Class 2 – carry up to 100 kg, maximal speed of 1.8 to 2.7 ms-1 , capable to carry up to 9° slope, travel over than 16 km on a single charge, climb a 50 mm obstacle, designed for indoor and moderate outdoor use.Class 3 – carry up to 113 kg, maximal speed of 1.8 to 2.7 ms-1 , capable to carry up to 9° slope, travel over than 16 km on a single charge, climb a 50 mm obstacle, designed for active indoor and outdoor use.Class 4 – carry up to 130 kg, maximal speed of 10 to 12 km/h , capable to carry up to 15° slope, travel over than 35 km on a single charge, climb a 150 mm obstacle, designed for active outdoor use in heavy terrains.

Page 5: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Scooter – an example

Front-wheel driven (for indoor use)

Rear-wheel driven (for indoor and outdoor use)

Scooter can be broken down to fit into the trunk of an automobile.

Page 6: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Powered wheelchair system Powered wheelchair system schematicschematic

Electromagnetic brakes immobilize the wheelchair in case of inclined ground surfaces

Page 7: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Motor selection:

•Armature controlled permanent magnet direct current motors – high torque, high start torque, simplest controlIn some prototypes:

•Brushless motors

•AC motors – special controllers, where the motor power is changed by varying the frequency of the motor supply.

Power rate of the DC motor – describes the ability of the motor to transfer electrical power to mechanical power.

Motor control of powered wheelchairDynamic stiffness – how closely a moving system follows a desired motion profile in the presence of disturbance torques.

Closed-loop systems are used to increase the dynamic stiffness.

Page 8: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Bandwidth – the limiting frequency of motion commands to which a system can respond

Speed contour of the controller

Typically – 150 -250 Hz

Servo controllers

M

Currentsensor

Switchingdrive

-+

-+

Velocityreference

Velocitysensor

Voltage control is used to control the motor speedCurrent contour (inner)Speed contour (outer)Switching (or chopper) drive

Page 9: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Switching drive:1. Unidirectional (half-bridge) – used in

scooters2. Bi-directional (full-bridge, H-bridge)

Switching drive:1. With dynamic braking2. Without dynamic braking

Speed reverse by relay

Pulse – width modulation (PWM)

Frequency – 5 -30 KHz

Page 10: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Motor current in the switch mode:

PulseGenerator

R

L DC

m

otor

1. Imax should be limited to 5 times the rated current of the motor to insure that demagnetization does not occur

2. The ripple (Imax – Imin)/Iaverage should be minimized to improve the form factor, and reduce the conduction loss in the switching devices.

Page 11: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Switching elements:1. Silicon controlled rectifiers (SCR) – old

constructions2. Powder metal oxide semiconductor field

effect transistors (MOSFETs)

•Powered wheelchairs based on SCR use typical switching frequencies of 500-1000 Hz.•Powered wheelchairs based on MOSFETs use typical switching frequencies of 5 -30 KHz. Efficiency – 90%.- excellent to battery application.

Page 12: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

Basic Full-bridge circuit

•High forward voltage (up to 50 V) on the MOSFETs transistors during the turn-off period due to the motor inductivity.•Multiple MOSFETs transistor in parallel in order to achieve big output currents.

Page 13: Lecture 19 Dimitar Stefanov Powered Wheelchairs 1940s – first powered wheelchairs, standard manual wheelchairs adapted with automobile starter motors.

•Typically - MOSFETs transistors rated at 100V and 30-50 A continuous operation. •In some constructions – up to 8 transistors, connected in parallel to increase the reliability of the wheelchair•Dynamic braking – special fast recovery diodes are switched in parallel of the MOSFETs and the motor ; During the braking process the current is returned back to the supply, i.e. the battery is charged during braking.