Actuators for Robots - Embedded Intelligent Robotics - Lecture Slides, Slides of Robotics

Download Actuators for Robots - Embedded Intelligent Robotics - Lecture Slides and more Slides Robotics in PDF only on Docsity! Jussi Suomela HUT/Automation 1 Actuators for Robots Actuators are used in order to produce mechanical movement in robots. docsity.com Actuators In this lecture we will present: Motor and Encoder H-Bridge  Pulse-Width-Modulation (PWM)  Servos Other robotic actuators docsity.com Jussi Suomela HUT/Automation 5 Servo System Servo is mechanism based on feedback control. The controlled quantity is mechanical. docsity.com Jussi Suomela HUT/Automation 6 Servo Control of an Electrical Motor docsity.com Jussi Suomela HUT/Automation 7 Properties of Servo  high maximum torque/force allows high (de)acceleration  high zero speed torque/force  high bandwidth provides accurate and fast control  works in all four quadrants  robustness docsity.com Jussi Suomela HUT/Automation 10 Electrical Actuator Types DC-motors brushless DC-motors asynchronous motors synchronous motors reluctance motors (stepper motors) docsity.com Jussi Suomela HUT/Automation 11 DC-Motors simple, cheap easy to control 1W - 1kW can be overloaded brushes wear  limited overloading on high speeds docsity.com DC-motor control Controller + H-bridge PWM-control Speed control by controlling motor current=torque Efficient small components PID control docsity.com H-Bridge Hardware Implementation with Microcontroller: 2 Digital output pins from microcontroller, [one at Gnd, one at Vcc] feed into a power amplifier Alternative: use only 1 digital output pin plus one inverter, then feed into a power amplifier docsity.com e a. 7 Power Amplifier “YF. MICROELECTRONICS L293D PUSH-PULL FOUR CHANNEL DRIVER WITH DIODES » 600mMA, OUTPUT CURRENT CAPABILITY PER CHANNEL 21.24 PEAK OUTPUT CURRENT (NON REPETITIVE) PER CHANNEL = ENABLE FACILITY » OVERTEMPERATURE PROTECTION ® LOGICAL "0" INPUT VOLTAGE UP TO 1.5v (HIGH NOISE IMMUNITY # INTERNAL CLAMPS DIODES DESCRIPTION The L293D is a monolithicintegrated high voltage, high current four channel vriver designed to accept standard DTL or TTL logic levels and drive induc- tive loads (such as relays solenoides, DC and stepping motors) and switching power transistors. To simplify use as two bridges is pair of channels is equiped withan enable input. Aseparate supply innput is provited formthe logic, allowing operation at Rd voltage and internal clamp diodes are included. Braun! 2004 PRELIMINARY DATA Powerdip 124242 ORDERING NUMBER : L293D, This device is suitable for use in switching applica- tions at frequencies up to 5 KHz. The L293D is assembled in a 16 lead plastic packege which has 4 center pins connected to- gether and used for heatsinking. docsity.com Power Amplifier BLOCK DIAGRAM e docsity.com Jussi Suomela HUT/Automation 20 Structure of an Asynchronous motor docsity.com Jussi Suomela HUT/Automation 21 Synchronous Motors usually big 100 kW - XXMW also small ones ~ brushless DC-motors from 50W to 100 kW controlled like as-motors (frequency) ships  industry Mobile machines docsity.com Stepper Motors docsity.com Stepper Motors  Stepper motors are another kind of motors that do not require feedback  A stepper motor can be incrementally driven, one step at a time, forward or backward  Stepper motor characteristics are: – Number of steps per revolution (e.g. 200 steps per revolution = 1.8° per step) – Max. number of steps per second (“stepping rate” = max speed)  Driving a stepper motor requires a 4 step switching sequence for full-step mode  Stepper motors can also be driven in 8 step switching sequence for half-step mode (higher resolution)  Step sequence can be very fast, the the resulting motion appears to be very smooth docsity.com Stepper Motors Full Step Sequence Step| A A’ B B’ 1 ON OFF ON OFF 2 ON OFF OFF ON 3 OFF ON OFF ON 4 OFF ON ON OFF A A B B’ Using two independent coils Clockwise rotation: 1,2,3,4,1,2,3,4... on motor shaft Counterclockwise: 4,3,2,1,4,3,2, 1... e” 23 ° ° ° ° ° ° décsity.com Stepper Motors Note: In full step sequence, A 1s always negated to A’ and B 1s always negated to B’ (this is different for half-step sequence) ¢ Therefore it is sufficient to use Step| A a B B’ only 2 control signals (the other 2 can be derived by NOT gates) 1 oe OF Pe OF 2 ON OFF OFF ON 1 2 3 4:31 2 3 4 3.| OFF ON OFF ON 4 OFF ON ON OFF A B Bréunl 2004 24 ® docsity.com 26in Motor and Encoder DC-Micromotors 2,1 Watt Precious Metal Commutation For combination with: Gearheads: 20/1, 22E, 22/2, 22/5, 22/6, 23/1, 38/3 Encoders: 10/09B, 10/09BP, 5500, 5540 Ayo aol! ee) 1 Nominal voltage 3 Volt 2 Terminal resistance R 0,6 193 o 3 Output power P2 max 3,69 2,01 w 4 Efficiency 1 max, 83 78 Yo 5 No-oad speed No 9600 8 200 rpm 6 No-load current (with shaft o 1,5 mm) lo 0,040 0,003 A 7 Stall torque My 14,70 9,37 mNm 8 Friction torque Mr 0,12 014 mNm 9 Speed constant kn 3 230 208 rpm 10 Back-EMF constant ke 0,310 4,810 mV/rpm 11 Torque constant koa 2,96 45,90 mNm/A 12 Current constant ki 0,338 0,022 AlmNm 13 Slope of n-M curve AnfAM, 653 875 rpmém Nm 14 Rotor inductance L 35 8 000 uH 15 Mechanical time constant Tm 25 22 ms 16 Rotor inertia J 3,70 2,40 gem? 17 Angular acceleration OL max. 40 39 -103rad/s? 18 Thermal resistance Rini/Rin2 4/28 knw 19 Thermal time constant Twiitwe 45/602 5 Operating temperature range: otor 30...+ 85 (optional - 55... + 125) c or, max. permissible +125 "c 2004 4 Data Fanthaher/Minim tousity.com Motor and Encoder Spur Gearheads Bre reduction ratio (nominal) 3, a7 a. 7 0, wo 54 97, 173 308 548 975 1734 3.088 5490 9780 17 386 30 969 55057 98.070 174 350 310 560 552 113 983 447 Braunl 2004 won a> ns ot weight without motor g 57 59 68 72 72 7 7 82 82 88 88 93 93 98 98 103 103 108 108 113 113 118 118 length without motor L2 mm 40,8 40,8 46,6 49,5 49,5 52,4 52,4 55,3 55,3 58,2 58,2 61,1 61,1 64,0 64,0 66,9 66,9 69,8 69,8 72,7 72,7 75,6 75,6 length with motor 2224R ul mn 45,4 45,4 50,0 53,6 536 56,5 56,5 59,4 594 62,3 62,3 65,2 65,2 68,1 68,1 71,0 71,0 739 739 76,8 768 797 797 2230 F u mm 51,2 51,2 55,8 59,4 59.4 62,3 623 65,2 65,2 68,1 68,1 71.0 71,0 73,9 73,9 76,8 76,8 79,7 79,7 82,6 82,6 85,5 85,5 2233 F ul mm 54,0 54,0 58,6 62,2 62,2 65,1 65,1 68,0 68,0 70,9 70,9 73.8 73,8 76,7 76,7 79,6 79.6 82,5 82,5 85,4 85,4 88,3 88,3 0,1.Nm For combination with: DC-Micromotors: 2224 SR, 2230, 2233 DC-Motor-Tacho Combinations: 2251...8 continuous operation M max. mNm 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 output torque intermittent operation M max. mNm 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 400 direction of rotation (reversible) efficiency Data Faulhaber/Minimotor docsity.com Motor and Encoder These incremental shaft encoders in combination with the FAULHABER DC-Micromotors are designed for indication and control of both, shaft velocity and direction of rotation as well as for positioning. The supply voltage for the encoder and the DC-Micromotor as well as the two channel output signals are interfaced with a 150 mm ribbon cable and a 10-pin connector. Solid state Hall sensors and a low inertia magnetic disc provide two Details for the DC-Micromotors and suitable reduction gearheads channels with 90° phase shift are on separate catalog pages TE el Wee ey ee c Pin Function P 1 + Motor + w 3 Channel a 3 J | Channel A 4° channel B = § GND a 6 * motor - E \ 2 vec i —— 3 - EI to - 5 S$ 5 s aa Channel AVB ma 7 tr, tf [ 3 q — 5 GND 5 17 Channel B : Rotation ae Output signals Output circuit Connector with clockwise rotation as seen from the shaft end Encoders 20B Encoders 21B Channel A leads B Cahnnel 6 leads A * Motors type 2842, 3042, 3557 have separate motor connectors (Panduit 050-010-455) Ribbon cable - PVC 6 conductors — 0,09 mm? Photos Faulhaber/Minimotor docsity.com Pulse-Width Modulation A/D converters are used for reading analog sensor signals Why not use D/A converter for motor control? – Too expensive (needs power circuitry) – Better do it by software, switching power on/off in intervals – This is called “Pulse-Width Modulation” or PWM docsity.com Pulse-Width Modulation tL I | od >, Vv | is equivalent to: low speed t 7 >. Vv | is equivalent to: high speed t Bein! 2004 15 ® docsity.com Pulse-Width Modulation How does this work? – We do not change the supplied voltage – Power is switched on/off at a certain pulse ratio matching the desired output power  Signal has very high frequency (e.g. 20kHz) Motors are relatively slow to respond – The only thing that counts is the supplied power – ⇒ Integral (Summation)  Pulse-Width Ratio = ton / tperiod docsity.com Servos B F F Servos  Terminology:  Do not confuse “servos” with “servo motors”  DC motors (brushed or brushless) are also sometimes also referred to as “servo motors”  See: http://www.theproductfinder.com/motors/bruser.htm  “So when does a motor become a servo motor? There are certain design criteria that are desired when building a servo motor, which enable the motor to more adequately handle the demands placed on a closed loop system.  First of all, servo systems need to rapidly respond to changes in speed and position, which require high acceleration and deceleration rates.  This calls for extremely high intermittent torque. docsity.com Servos  As you may know, torque is related to current in the brushed servo motor.  So the designers need to keep in mind the ability of the motor to handle short bursts of very high current, which can be many times greater than the continuous current requirements.  Another key characteristic of the brushed servo motor is a high torque to inertia ratio.  This ratio is an important factor in determining motor responsiveness.  Further, servo motors need to respond to small changes in the control signal.  So the design requires reaction to small voltage variations.” docsity.com Jussi Suomela HUT/Automation 45 Hydraulic motor docsity.com Jussi Suomela HUT/Automation 46 Hydraulic Valves  servo valves – complicated structure, expensive – good control  proportional valves – simple, cheap – robust – more difficult to control Digital hydraulics, new! – several fast on/off valves (2n) – digital control of the flow docsity.com Servo Valve Valve responding to change in electrical input Valve condition following change docsity.com Jussi Suomela HUT/Automation 50 Other Actuators piezoelectric magnetic ultra sound SMA  inertial docsity.com Examples Ge iea Col aera) docsity.com Arska docsity.com