SSY300 - APPLIED MECHATRONICS

LECTURE 8 – ACTUATORS 2 NIKOLCE MURGOVSKI

Learning outcomes: • Understand the principles of how electrical actuators work, especially DC motors. • Be able to select a suitable electric actuator and gearing to a mechatronic system. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 2

OUTLINE

• Repetition • Continuation on DC-motor • Other types of motors • Gearing • Selection of motor DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 3

ELECTROMECHANICAL ACTUATOR Voice coil •Convert electrical energy to mechanical energy.

Relay

Motor

Solenoids DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 4

PMDC MOTORS

• 푈푠 − 푅퐼 − 퐿 퐼ሶ − ke휔 = 0 푘 푘 푘 퐼ሶ = 0 ⇒ 푀 = 푘 퐼 = 푡 푈 − 푡 푒 휔 • At steady state: 푡 푅 푠 푅 DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 5

PROS AND CONS OF PMDC

+Lighter and smaller than other DC motors. +Work in both direction (can change direction of rotation). +Easy to control due to the linearity. ‒Brushes will wear (if possessed). DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 6

QUIZ ON ACTUATORS 2

1. What is the torque produced by a force of 40 N acting at 20 cm? 2. An drives a wheel through a gearing system that has an efficiency of 90%. If the motor produces power of 10 kW, what is the power delivered to the wheel?

• Answer: 1. Torque is the product of force and distance: 푀 = 8 Nm. 2. 10 % of the power is lost in the gearbox; hence, 9 kW is delivered to the wheel. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 7

QUESTION OF THE DAY

A PMDC motor gives constant power to a load at varying speeds. Which of the motor curves represent the constant power delivered by the motor?

a) b) c) d) DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 8 푃 푀 = • Motor torque is computed as 휔. • When P is constant, the curve expressing the torque is a hyperbola. • Correct answer is c). DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 9

DAILY DICTIONARY

• Ställdon • Actuator • Transmission • Transmission • Spole • Coil • Kommutator • • Permeabilitet • Permeability • Lager • Bearing • Borstlösa • Brushless • Startmoment • Stall torque • Brygga • Bridge • Stegmotor • • Tröghetsmoment • Moment of inertia • Fältlidning • Field winding • Ankar • DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 10

ACTUATORS 2

Human-machine interaction

Micro controller/processor Filter Software Hardware/ Automatic electronics control Sensors

Electromechanical Transmission/ Drivers Load actuator gearbox

Mechatronic module

Energy source DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 11

SERVO MOTOR

• Type of PMDC motor with a position or speed control. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 12

STEPPER MOTOR

• Type of a DC motor that moves one pole at a time. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 13 DC MOTORS WITHOUT A PERMANENT : SHUNT MOTOR • Armature () and field ) windings are connected in parallel. +Almost constant speed on a wide range of loading. +Cheap way to control the speed, by placing a potentiometer in series with the field winding. ‒Low stall torque. ‒Needs brushes. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 14 DC MOTORS WITHOUT A PERMANENT MAGNET: SERIES MOTOR • Armature and field windings are connected in series. +Very high stall torque. +Can provide constant power. ‒No maximum speed, i.e. the motor can fail if not connected to a load. ‒Needs brushes. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 15 DC MOTORS WITHOUT A PERMANENT MAGNET: COMPOUND MOTOR • Includes both parallel and series windings. +Positive characteristics of both shunt and series motors. ‒Needs brushes. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 16 CONTROL OF PMDC MOTOR WITH A LINEAR AMPLIFIER

• A small current 퐼퐵 is used to control a large current 퐼퐶. • The diode is called a free-wheeling diode. It is used to eliminate voltage spike when power source is removed. • A problem with this type of control is the power losses in the transistor, since the transistor is operated in its linear region. • To decrease losses, we would like to operate the transistor either in cutoff or saturation. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 17 • Why do we need the free- wheeling diode over the motor? • Motor is running, diode is reverse biased, 푈퐿 = 퐿퐼ሶ = 0.

• Without diode: transistor is in cutoff, 푈퐿 = 퐿퐼ሶ → ∞, as 퐼 changes value from 0 to maximum in an instant. This will generate an electric arc (spark) over the switch.

• With diode: circuit is closed through the diode. No spark and the motor is free-wheeling. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 18

PULSE WIDTH MODULATION (PWM)

• The transistor is either saturated or in cutoff (ON or OFF). 1 푓 = > 1 kHz • High switching frequency 푇 . • Speed is controlled by controlling impulse duration 휏. The ratio 휏 duty cycle = 100 % 푇 is called duty cycle. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 19

CHANGING DIRECTION OF MOTION

• H-bridge is used to change direction of motion. • Two transistors are activated at the same time. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 20

HISTORY OF AC MOTORS

Jonas Wenström 1855–1893 Patent on 3-phase AC in 1889, the Schematic drawing of Galileo Ferraris' first basis of ASEA (ABB). Might have from his patent application, Sketch from Wenström's patent invented the electric light. 1885. application, 1890.

Tesla’s induction motor, ca 1887. Still on display in the British Michael Dolivo-Dobrowolsky's first Science Museum in London. three-phase cage-induction motor, 1889. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 21

GEARING

• Motors usually have better performance at high speed and low torque. • Gear box or belt drive are often needed to match motor output to the load requirements. • If 푁 is gearing, then motor speed is about 푁 times greater than load speed and load torque is about 푁 times greater than motor torque 푀 휔 ~푁휔 , 푀 ~ 푙 푚 푙 푚 푁 DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 22 • Gearing is defined by gear ratio N and efficiency 휂. Then, for the system below, it holds 휔푚 = 푁휔푙 1 퐽 푀 퐽 휔ሶ + 퐽 휔ሶ + 푀 = 퐽 + 푙 휔ሶ + 푙 , 휔ሶ ≥ 0 푚 푚 푁휂 푙 푙 푙 푚 휂푁2 푚 휂푁 푙 푀 = 푚 휂 휂퐽 휂푀 퐽 휔ሶ + 퐽 휔ሶ + 푀 = 퐽 + 푙 휔ሶ + 푙 , 휔ሶ < 0 푚 푚 푁 푙 푙 푙 푚 푁2 푚 푁 푙 DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 23 SELECT ACTUATOR, GEARBOX, SENSORS, ENERGY SOURCE • How does the load look like? • Constant or variable speed? Speed • Acceleration? • Moment of inertia? • Load Torque? • Power requirement? Time • Need a gearing/transmission? • What is the maximum engine speed? • How big stall torque? • Type of energy source? • Is accurate position or speed control needed? DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 24

THE LOAD

• How is the load characterized? • Working cycle.

Speed

Time DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 25

EXAMPLE: MOTOR SELECTION

• Choose a suitable motor from a given data sheet, such that it can drive a load that consists of a friction 푀푙 = 퐵휔푙, where 퐵 = 0.12 mNms/rad. The system should work at 휔푙 = 3500 rpm, without the need for gearing. The motor acceleration to the desired speed is not of interest. Assume that motor and load inertia can be neglected. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 26 DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 27

• No gearing: 푁 = 1, ⇒ 휔푙 = 휔푚 휋 푀 = 푀 = 퐵휔 = 0.00012 ⋅ 3500 ⋅ = 44 mNm • Torque: 푚 푙 푙 30 . 휋 푃 = 푃 = 휔 푀 = 3500 ⋅ ⋅ 0.044 = 16.12 W • Power: 푚 푙 푙 푙 30 . 1 푇 푀 = ׬ 푀2 푡 푑푡 = 44 mNm • Rated (root-mean-square) torque: 푟푚푠 푇 0 푚 . • RMS torque is needed to prevent motor overheating in continuous operation. • Since there is only one operating point, the operating torque is the RMS torque. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 28 • Working point below max. torque lines, so all motors are OK. • Rated power: SB4045 NOT OK (10.4 W < 16.12 W), all other are OK. • Rated torque: SB4045 and SB4060 NOT OK, all others are OK. • 4 Select, e.g., the cheapest feasible motor, SB4078. • SB4060 could be OK if gearing was allowed. Why? • An ideal gearing does not change motor power, but it does change the torque-speed operating point. In this example the gearing will move the operating point towards higher speed and lower torque. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 29

SUMMARY

• Basic principles of how electrical actuators work. • Motor drives and gearing. • Motor selection for a mechatronic system. DIVISION OF SYSTEMS AND CONTROL, DEPARTMENT OF ELECTRICAL ENGINEERING SSY300 APPLIED MECHATRONICS NIKOLCE MURGOVSKI 30

HOME ASSIGNMENT

• Home assignment: Design and selection of electric motor and gearbox • Deadline: May, 10.