Machine Drives Module 3.06 Introduction

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Machine DrivesModule 3.06Introduction

• Lecturer
• Dr Vesna Brujic-Okretic
• (in place of Professor Graham Parker)
• Ext 9676 and 9681
• Email mes1vb_at_surrey.ac.uk

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Course Overview

• Introduction Overview
• Power control devices
• Motor basics
• DC motor drives
• steady-state characteristics
• dynamic characteristics
• DC servomotor analysis
• Novel drives a case study
• Fluid drives
• Basic hydraulic control systems
• Hydraulic servo-valves
• cylinder systems motor systems

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The Course Objectives

• To learn about a variety of machine drives
• To be able to compare
• electrical
• hydraulic drive systems
• To be able to analyse and model electrical and
  hydraulic servo systems
• To apply knowledge to the design of drive systems
  for particular applications

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The definition

• Machine drives and actuators are devices which
  perform the final output stage of a control
  system and involve motion.
• They provide a means of conversion from the
  statement of intention, expressed as an
  electrical input, to the end effect
• external environment is sensed and the system
  responds by directing the actuator to make a
  change (or produce a physical effect) within the
  external environment

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The classification

• It is logical to begin a consideration of drives
  and actuators by classifying the ways in which
  motion can be produced
• The principal division lies between
• rotational, and
• linear (translation) devices
• Motion converters, such as gearboxes (rotational)
  or rack and pinion systems (linear) are being
  added (to motors) as appropriate

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Main types of power transmission

• There are 4 main types of power transmission
• Mechanical
• Electrical
• Hydraulic
• Pneumatic

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Classes of Applications

• Manufacturing
• Domestic
• Automobiles
• Autonomous and remotely controlled vehicles
• Information Technology
• Healthcare

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Manufacturing

• to move materials and parts for processing and
  assembly
• milling machines
• CNC machines powered by electric or hydraulic
  motors.
• robots or manipulators - electric or hydraulic.
• A familiar example pick and place robot
• etc.

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Domestic

• Mostly electric motors
• Such devices include
• the coffee grinder,
• dishwasher, vacuum cleaner, sewing machine,
• video recorder, CD player, camera,
• personal computer,
• power tools,
• electric razors,
• etc.

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Automobiles

• both electric and hydraulic, e.g.
• steering and suspension systems.
• electric windows,
• central door locking, sunroof operation,
• mirror positioning, etc.
• Some top of the range vehicles use in excess of
  one hundred motors.

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Autonomous and remotely controlled vehicles

• Mostly use electric motors for
• movement of the vehicle and
• the steering mechanism.
• Some vehicles are remotely controlled for use in
  hazardous environments such as
• firefighting and bomb disposal. These may have
  alternative drive mechanisms such as pneumatic,
  for safety reasons.

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Information Technology

• Motors are found in abundance in IT equipment
• Personal computers
• disk drives,
• CD drives,
• floppy drives etc.
• Printers,
• Fax machines, etc.

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Healthcare

• specialist healthcare equipment
• the dentists drill is commonly pneumatic
  although some are being replaced with very small
  electric motors.
• Electric wheelchairs are now much more common
  than they used to be, due in part to improved
  battery technology.
• Dialysis pumps etc.

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Applications by electric motor used

• CORELESS DC MOTORS
• Dialysis pumps
• Money changers, sorters
• Card readers
• Ticket printers
• Security Systems
• Film winders
• Robots, educational robots

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Applications by electric motor used

• IRON CORE DC MOTORS
• Positioning systems
• Vending devices
• Printing machines
• Syringe pumps
• Dispensers
• Locking systems

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Applications by electric motor used

• BRUSHLESS DC MOTORS
• Infusion pumps, insulin pumps
• Analysis dialysis equipment
• Scanners
• Laser measuring equipment
• Camera shutter
• Motorised valves

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Applications by electric motor used

• PM STEPPER AND SYNCHRONOUS MOTORS
• Throttle body adjustment
• Card reader
• Valve control
• High quality record players
• Respiratory equipment (hospital)
• Shutter controls

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• The Background

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The background

• Radical changes in motors and drives have taken
  place over the last 20 years
• Different types of motors continued to be
  developed and each became associated with certain
  type of application.
• For example
• traction is associated almost exclusively with
  series DC motor (high starting torque)
• shunt DC and cage induction AC motors - with
  applications requiring constant speed

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The background

• There was no easy way of varying the supply
  voltage and/or frequency to obtain speed control
• so the ways of controlling speed was sought
  within the motor itself
• 1960s Power Electronics
• in the 1960s power electronics started to make an
  impact. The advent of thyristor allowed for a
  variable voltage supply to be employed in the
  armature circuit of a DC motor

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The background

• 1970's
• Variable Frequency Inverters
• In the 1970s variable-frequency inverters made
  second breakthrough allowing the induction motor
  - previously usable for constant-speed
  applications only - to be used in the
  controlled-speed applications
• In effect, the emphasis has now shifted from
  complexity inside the motor to sophistication in
  supply and control arrangements

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• The motion control

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The motion control

• Depending on the application, motion control can
  refer to
• simple on-off control or
• a sequencing of events,
• controlling the speed of a motor,
• moving objects from one point to another
• precisely constraining the speed, acceleration,
  and position of a system throughout a move

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Controlled actuation
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• The concept of a
• DRIVE SYSTEM

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Drive system

• In order to produce the required motion we need
  additional circuitry - apart from the motor
  itself - to drive and control the system
• They are referred to as power converter circuits
  
• The converter draws electrical energy from the
  source (e.g. mains) and supplies it to the motor
  at whatever voltage and frequency is necessary to
  achieve the required mechanical output

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Drive system general arrangement

• General arrangement of a drive system is
  presented below

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Basic Drive Components

• Usually, there are 2 distinct parts
• power stage, and
• control section
• Control signals tell the converter what to do
  while feedback signals are used to measure what
  is actually happening
• Comparing the demand and the feedback signals the
  target output is maintained

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Prime movers versus electrical motors

• The term prime mover is reserved for those
  devices, such as steam turbines and diesel
  engines, which convert chemical energy in fuel
  (or other natural sources - e.g. wind, water)
  into mechanical movement that will eventually
  lead to producing electrical power
• electrical power is then utilised (in industry,
  for example) as the most usual means of
  conversion into mechanical work (electrical
  motors)

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Mechanical components

• Mechanical components, such as
• Gearboxes and
• Leadscrews
• are used to match the characteristics of
• power devices to the load characteristics
• of the machine

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Selecting a drive Primary considerations

• Requirements
• Acceleration and deceleration
• Velocity
• Responsiveness
• Operational Power (Force/Torque)
• Performance under varying load

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Selecting a drive Secondary considerations

• Constraints
• Space envelope and shape
• Weight and power to weight
• Cost
• Environmental requirements
• Noise emission
• Spark emission (flammable area)
• Vibration (emitted and received)

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Selecting a drive Secondary considerations

• Electricity supply (DC, AC, single phase, etc.)
• Electromagnetic compatibility (EU regulation)
• Ergonomics
• Simplicity of maintenance and repair
• Safety
• Reliability
• Power loss / efficiency
• Reversibility
• Rate of response
• Resolution, accuracy, repeatability

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Rotary drives
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Linear drives
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• Motor gearbox

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Motor gearbox
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Referred Inertia
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Referred Inertia

• The total inertia that the motor must overcome
  is
• similarly, the inertia at the load shaft is