Drehzahl- und Positionsgeber als Rückführzweig in geregelten Antrieben

Transcription

1 Technische Universität München Vorlesung Elektrische Aktoren und Sensoren in geregelten Antrieben Drehzahl- und Positionsgeber als Rückführzweig in geregelten Antrieben Prof. Dr. Ing. Ralph Kennel Elektrische Antriebssysteme und Leistungselektronik

2 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 2

3 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 3

4 Anwendungsbeispiel : Werkzeugmaschinen Haupt(spindel)antrieb(e) für die Bearbeitungsenergie Vorschubantriebe für die Positionierung Synchronmaschinen mit Drehgebern!!! 4

5 Synchronmaschine mit Drehgeber 5

6 Montageorte von Positionsgebern 6

7 Linear Scales Advantages exact/direct measurement small disturbances Disadvantages high cost low robustness 7

8 Encoders Advantages low cost high accuracy (by gear ratio) encoder type ERN, Heidenhain Disadvantages elasticities and back-lash (in the drive train) are neglected 8

9 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 9

10 speed M-Regler controller current Stromcontrollers Regler AC drive control n* i* q - * 0 i* d - e j M 3~ Feldschwächung field weakening - - field Feld-Regler controller machine Maschinenmodell for asynchronous machines e -j e -j i u Encoder for synchronous machines 10

11 (simplified) basic structure of a drive control s* Lageregelung Drehzahlregelung controller Regelung speed Drehmoment-/Strom torque/current position controller controller n* i* s n i M 3~ Kommutierungssignale commutation signals tacho Tacho generator position Lagegeber encoder digital control : a single encoder for all feedbacks!?! 11

12 Velocity Sensors Ralph Kennel

13 Tacho (Huebner Berlin) Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

14 Tachogenerator The tachogenerator armature (= rotor) is connected as torsionally rigid as possible to the driving machine, whose speed is to be detected. u G (n) As the armature rotates in the field of the permanent magnets, voltages are induced in the armature winding. These voltages are tapped at the commutator with special brushes (polarity dependent on direction of rotation). Available at the terminals is a noload voltage U 0 (n), which is proportional to the speed. Tachogenerator speed-voltage characteristic. n This is physically a very linear characteristic! For obtaining this signal, in difference to other speed sensors an auxiliary power (voltage supply) is not necessary. Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

15 Tachogenerator equivalent circuit diagram of tachogenerator with subsequent control electronics. G R A u G (n) L A A 1 u(n) R L R C A 2 If the tachogenerator is loaded with the load resistance R L or load current I L (terminals A1 and A2), the voltage is reduced by the voltage drop due to the armature resistance R A U(n) = U 0 (n) I L R A = U 0 (n) R L /(R A + R L ) Usually the load resistance R L is significantly higher than the armature resistance R A, so that the following approximation applies U(n) U 0 (n) for R L >>R A Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

16 Tachogenerator equivalent circuit diagram of tachogenerator with subsequent control electronics. G R A u G (n) L A A 1 u(n) R L R C A 2 If the tachogenerator is loaded with the load resistance R L or load current I L (terminals A1 and A2), the voltage is reduced by the voltage drop due to the armature resistance R A U(n) = U 0 (n) I L R A = U 0 (n) R L /(R A + R L ) Usually the load resistance R L is significantly higher than the armature resistance R A, so that the following approximation applies usually the rated output voltage of a tachogenerator U(n) U 0 (n) for R L >>R is specified with respect to a defined load resistor A Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

17 Tacho (Huebner Berlin) Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

18 Tacho (Huebner Berlin) silver track on commutator good solution! a brushed tachogenerator in a brushless drive does that make sense??? Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

19 Ripple of tachogenerators The tacho generator DC voltage is superposed with small ripple voltages u pp, the frequency and amplitude of which depends on the speed, number of poles (number of magnetic poles), number of armature slots and number of commutator segments. ripple Incorrect installation of the tacho generator on the driving machine can increase the ripple. For this reason, special attention must be paid to correct installation incorrect mounting Prof. Dr. -Ing. J. M. Pacas, Universität Siegen

20 s* (simplified) basic structure of a drive position Lageregelung controller control speed Drehzahlregelung controller n* i* s n Drehmoment-/Strom torque/current controller Regelung i M 3~ Kommutierungssignale commutation signals tacho Tacho generator position Lagegeber encoder digital control : a single encoder for all feedbacks!?! 20

21 position controller speed controller torque/current controller servo motor s* n* i* s n i M 3~ commutation current signals distribution tacho generator position encoder the encoder has to meet the requirements with respect to all 3 (!) signal types speed signal position signal encoder 21

22 Requirements for Encoders replacing 3 different systems commutation encoder tacho generator position encoder by a single encoder has serious impact on the requirements for the single encoders!!! (because the needs of all feedback loops have to be fulfilled) 22

23 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 23

24 Zusammenhang klar J! Genauigkeit Auflösung? Zusammenhang teilweise klar?? Zusammenhang unklar differentielle Genauigkeit L??? was ist das??? 24

25 Accuracy of Position/Speed Encoders Position difference between the actual (real) position (angle) and the position (angle) measured by the encoder (e. g. position of lines) Speed difference between the actual (real) speed and the speed measured by the encoder (e. g. voltage of tacho generator) 25

26 Resolution of Position/Speed Encoders Position number of different positions (angles) the encoder is able to distinguish Speed number of different speeds the encoder is able to distinguish (e. g. number of lines) (e. g. minimum voltage of tacho generator) 26

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30 Resolution and Accuracy of Incremental Encoders (mathematical description) resolution r dr n r 0 dx only absolute!!! a differential resolution does not make any sense! (absolute) accuracy a x ref,i i xreal,i xref,i x n x / n x real i real real,i (differential) accuracy a x real,i x real,i-1 i real i / n real / n x n by any calcution it is not possible to make these equations identical the respective characteristics are physically really different!!! x x real,i i x x real,i-1 real 1 30

31 Development of Accuracy and Resolution during the recent decades feedback sensor 1980 s 1990 s 2000 s accuracy resolution accuracy resolution accuracy resolution position sensor for position control medium medium (10.000) medium high ( ) speed sensor for speed control position sensor for current control low high medium high high low (18) high medium (1.000) very high? very high? 31

32 Requirements for Simultaneous Position and Speed Measurement (for being competitve to an analogue tacho generator) of course, higher differential accuracy can be gained by increasing the resolution this means, however, an extraordinary high resolution! 32

33 Requirements for Simultaneous Position and Speed Measurement (for being competitve to an analogue tacho generator) position : accuracy of 0,001 speed : speed range : resolution : 0, rpm 0,001 rpm at speeds < 0,1 rpm in combination with a controller cycle time of 50 µs this results in a resolution demand for the encoder of 30 Bit!! 33

34 cost Resolution of position/speed encoders this point describes the extraordinary requirements (30 bits resolution) mentioned before during the recent decades $ 500 resolution 34

35 cost Resolution of position/speed encoders during the recent decades incremental encoders were the industrial standard in the 1980 s $ 500 resolution 35

36 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 36

37 Resolver injection of a stationary (sinusoidal) high frequency signal sensing of a twodimensional stationary (sinusoidal) signal response Tamagawa R1 S2 u 1 ( 0 Stator u e Rotor u R Stator u 2 R2 S1 Stator u 1 S3 S4 u 2 ( 0 Page 37

38 Resolver injection of a stationary (sinusoidal) high frequency signal sensing of a twodimensional stationary (sinusoidal) signal response Tamagawa R1 S2 u 1 ( 0 Stator u e Rotor u R Stator u 2 R2 S1 Stator u 1 S3 S4 u 2 ( 0 Page 38

39 Resolver injection of a stationary (sinusoidal) high frequency signal sensing of a twodimensional stationary (sinusoidal) signal response Tamagawa R1 S2 u 1 ( 0 Stator u e Rotor u R Stator u 2 R2 S1 Stator u 1 S3 S4 u 2 ( 0 Page 39

40 cost Resolution of position/speed resolvers are an industrial standard in low performance servo drives today encoders during the recent decades $ 500 SRS64 resolution 40

41 Tooth wheel encoder (reluctance resolver) resolution : positions per revolution (ca. 19 Bit) 41

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44 inductive (magnetic) encoder Heidenhain resolution : 18 Bit ( positions per revolution) 44

45 inductive (magnetic) encoder Heidenhain 45

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48 (Optical) Incremental Encoder photo elements LED optical grid next slide encoder disc reference marker ball bearing Heidenhain 48

49 Measuring Principle of Optical Incremental Encoders 49

50 Incremental encoder (with rectangular signals) 360 /p track Spur A track B Spur B multiplication of resolution 4-fach Auswertung zero marker Null- Impuls track A Spur A track B Spur B signal Logik processing 4-fach Auswertung 4x resolution signal Drehrichtung direction 50

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54 a real incremental encoder with rectangular output signal has a characteristic more like right side! by nature Encoder : better Discs differential (Optical accuracy Toothwheels) good for speed control 54

55 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 55

56 Incremental encoder (with sinusoidal signals) 360 /p track Spur Spur A track B Spur Spur B multiplication of resolution 4-fach- Auswertung zero marker Reference Nullmark Impuls track A Spur A track B Spur B Dig signal Logik itale processing Logik 4-fach-Auswertung Auswertung 4x resolution signal Drehrichtung direction direction 56

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58 cost $ 500 Resolution of position/speed encoders during the recent decades Resolution of position/speed encoders high resolution optical encoders are an industrial standard in high performance servo drives today during the recent decades resolution 58

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63 Track B Position Interpolation (Incremental Encoders with Sinusoidal Signals) Track A 360 / line /pulse number (= 1 increment) 63

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68 High Resolution Encoders with Sinusoidal Output Signals in x-y Projection - Real Measurements ROD RON

69 by nature : better absolute accuracy good for position control ROD RON a real high resolution encoder with sinusoidal output signal has a characteristic more like left side!! 69 15

70 Accuracy of Resolver and Optical Encoder 70

71 cost Resolution of position/speed encoders during the recent decades resolvers as well as high resolution optical encoders lie well below the cost-line accepted by the market $ 500 resolution 71

72 Reasons for Good Control Behaviour of Servo Drives with Digital Control Commutation Effects of Brushless Tachogenerators Effect of a Superposed Position Control Loop Significance of Differential Accuracy 72

73 Reasons for Good Control Behaviour of Servo Drives with Digital Control Commutation Effects of Brushless Tachogenerators Effect of a Superposed Position Control Loop Significance of Differential Accuracy 73

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78 Reasons for Good Control Behaviour of Servo Drives with Digital Control Commutation Effects of Brushless Tachogenerators Effect of a Superposed Position Control Loop Significance of Differential Accuracy 78

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83 Reasons for Good Control Behaviour of Servo Drives with Digital Control Commutation Effects of Brushless Tachogenerators Effect of a Superposed Position Control Loop Significance of Differential Accuracy see explanations above 83

84 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 84

85 cost Resolution of position/speed encoders during the recent decades which attempts have been made to get further improvements?? $ 500 resolution 85

86 (Actual) Publications Wen-Hong Zhu, Tom Lamarche : Velocity Estimation by Using Position and Acceleration Sensors IEEE-IES Transactions, vol. 54, No. 5, September/October 2007 (the need for a real speed signal leads to an additional acceleration sensor) Several years ago there was the proposal to use an additional analogue tacho generator (with silver commutation track) as speed sensor the problem still is not solved sufficiently 86

87 Possible Encoder Technologies encoders magnetic optical capacitive resolver tooth wheel incremental encoder absolute encoder interferometric encoder variable electrodes variable dielectricum Resolvers with low pole number Resolvers with high pole number pseudo absolute encoder PRC coded encoder reflecting encoder with CCD homodyne interferometric encoder heterodyne interferometric encoder Encoder Technologies 87

88 Tacoder Principle invented and introduced to the market some 15 years ago in difference to incremental encoders with sinusoidal outputs, where the position information is coded in the amplitude ratio of 2 orthogonal sine waves, the Tacoder uses the phase angle between two digital signals to code the position information 88

89 Tacoder Basic Idea 1 line optical receiver (standard) incremental encoder A B C interpolation of resolution by factor 4 optical disc 1 line reference oscillator 200 khz phase/ frequency modulation f 0 f T interpolation of resolution by factor

90 the Tacoder principle was invented and introduced to the market some 15 years ago in difference to the version with sinusoidal outputs, where the position information is included in the amplitudes of sine waves, the Tacoder uses the phase angle between two digital signals to code the position the improvement of the Tacoder concept can be understood when listening to radio programs. The quality of the sound is significantly better, when frequency modulation (FM) or phase modulation is used for transmission instead of amplitude modulation (AM). Electromagnetic disturbances do impact the phase or frequency of a signal much less than its amplitude. This effect was used by the Tacoder. 90

91 Tacoder position information encoded in phase between two digital signals 91

92 Tacoder Signal Processing by a simple ASIC Bus to the (Micro-)Controller 16 D 4 A 4 C Tacoder ASIC 10 T Tacoder M Motor 92

93 the Tacoder provided the following characteristics high speed range digital output signals (good disturbance ratio) high differential accuracy (like incremental encoders) low speed range digital output signals (good disturbance ratio) high resolution (like sinusoidal encoders) 93

94 cost Resolution of position/speed encoders during the recent decades $ 500 resolution 94

95 the Tacoder was not really successful in the market of servo drives!!! why? phase modulated signals cannot be synchronized with the cycle period of the controller market leader for encoder systems has decided to promote encoder systems with sinusoidal outputs 95

96 Encoder encoders Technologies magnetic optical capacitive resolver tooth wheel incremental encoder absolute encoder interferometric encoder variable electrodes variable dielectricum Resolvers with low pole number Resolvers with high pole number pseudo absolute encoder PRC coded encoder reflecting encoder with CCD homodyne interferometric encoder heterodyne interferometric encoder have the capability to provide high resolution as well as robustness 96

97 Capacitive Encoders shaped form of electrode(s) similar design to optical encoders drum or disc with shaped electrode mounted on the shaft tube or 2 nd disc with shaped electrode fixed at the stator (housing) the size of the electrode areas in direct oppostion changes with motion shaped form of dielectricum drum or disc with shaped electrode fixed at the stator (housing) tube or 2 nd disc with non-shaped electrode also fixed at the stator (housing) shaped dielectric tube or disc mounted on the shaft the dielectric charactersitic between the electrodes changes with motion detection of varying capacitance by a high frequency signal 97

98 Capacitive position sensor Prof. Dr. -Ing. J. M. Pacas, Universität Siegen Prof. Dr. -Ing. R. M. Kennel, Technische Universität München

99 neu am Markt : ein kapazitiver Geber Quelle : SICK/Stegmann 99

100 Capacitive Encoder Topologies 2-Plate Capacitive Encoder (shaped form of electrode) 3-Plate Capacitive Encoder (shaped form of dielectricum) 100

101 Components of Capacitive Sensing Element Multi-Electrode Transmitter Rotor (shaped form of dielectricum) Holistic Receiver 101

102 Grobspur (3 Signalperioden/Umdr.) Quelle : SICK/Stegmann Dielektrischer Rotor Feinspur (16 Signalperioden/Umdr.) leitende Empfänger Fläche 102

103 Signal Electronics of Capacitive Encoder (1 channel only) Excitation Generator Sensor Charge Amplifier Post Amplifier Synchronous Demodulator Low Pass Filter Driver Tx PCB Rotor Rx PCB Sine Cosine 103

104 Position Detection: Sine/Cosine, Coarse/Fine Track Fine Track Dielectric Rotor Multi-Electrode Transmitter PCB Coarse Track Sine & Cosine Signals of Fine Track (16 Periods per Revolution) Sine & Cosine Signals of Coarse Track (3 Periods per Revolution) 104

105 Prinzip: Sinus/Cosinus, Grob-/Feinspur Fein Quelle : SICK/Stegmann Grob 105

106 Experimental Setup Encoder under Test (EUT) Mechanical Jig for Controlled Manipulation of Axial as well as Radial Displacements (EUT vs. Shaft) Precision Index Table 106

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110 Large Hollow Shaft Encoder Sensor Electronics Ø ~ 300mm Scale 110

111 angular error [ ] Position Angular Error Experimental Results Large Hollow Shaft Encoder Absolute Accuracy (non-holistic design!) 230 angular position [ ] 111

112 Meßbereich measuring area Auflösung resolution Robustheit robustness Massenproduktion mass production on mass production magnetisch magnetic Resolver : am Umfang/ circular Zahnrad/tooth wheel : punktförmig/point niedrig low (multipole Resolver: 20 Bit) gut good schlecht bad optisch optisch optical optical punktförmig point hoch high (CCD: > 30 Bit) problematisch (temperatur- und stoßempfindlich) problematic (sensitive to shock and temperature) sehr gut (fotografische Herstellung) very good (photographic production) kapazitive capacitive am Umfang circular Zu wenig Erfahrung, um konkrete Aussagen zu machen. Too less experience to make knowledge-based statements. hoch high gut good gut good 112

113 Possible Encoder Technologies encoders magnetic optical capacitive resolver tooth wheel incremental encoder absolute encoder interferometric encoder variable electrodes variable dielectricum Resolvers with low pole number Resolvers with high pole number pseudo absolute encoder PRC coded encoder reflecting encoder with CCD homodyne interferometric encoder heterodyne interferometric encoder have the capability to provide ultra high resolution 113

114 why are interferometric encoders promising? actual encoder concepts physically measure position and then gain speed by mathematical derivation in interferometric encoders two laser beams one as reference, the other reflected by the moving object are compared with respect to their phase shift interferometric encoders provide the capability to physically measure speed first attempts have been made (see next slides) and basically confirm technical expectations but concepts are not yet mature to be used in industry 114

115 Possible Encoder Technologies encoders magnetic optical capacitive resolver tooth wheel incremental encoder absolute encoder interferometric encoder variable electrodes variable dielectricum Resolvers with low pole number Resolvers with high pole number pseudo absolute encoder PRC coded encoder homodyne interferometric encoder heterodyne interferometric encoder reflecting encoder with CCD 115

116 Homodyne Interferometric Encoder some years ago a concept was developped and tested technical description in : P. Drabarek, W. Meister, R. Kennel, M. van Keulen, Offenlegungsschrift DE A1, Deutsches Patentamt München measurements (see next slide) showed technical capabilities to be very convincing cost estimation/projection was a serious problem 116

117 Interferometric Sensor for Very High Resolution track with measuring grid 117

118 Comparison of Signal Noise (Position Accuracy) between a Homodyne Interferometric Encoder and a High Resolution Optical Encoder Interferometric Encoder High Resolution Incremental Encoder 118

119 cost Resolution of position/speed encoders during the recent decades $ 500 resolution 119

120 cost homodyne interferometric encoders provide significant improvement in resolution - estimated cost (based on realistic piece number) to high $ 500 resolution 120

121 Possible Encoder Technologies encoders magnetic optical capacitive resolver tooth wheel incremental encoder absolute encoder interferometric encoder variable electrodes variable dielectricum Resolvers with low pole number Resolvers with high pole number pseudo absolute encoder PRC coded encoder homodyne interferometric encoder heterodyne interferometric encoder reflecting encoder with CCD 121

122 Integrated (i. e. on-chip) Interferometric Sensor a concept idea laser diode beam splitter acousto-optical mode converters beam splitter photo diodes optical lenses measured object motion 122

123 Low Cost (Heterodyne) Interferometric Sensor laser diode another concept idea integrated opto-electononic chip any non-ideal metallic surface 123

124 angle in arcsec Comparison of Angle (Position) Accuracy between a Heterodyne Interferometric Encoder and a High Resolution Optical Encoder tolerance band of incremental encoder error overall tolerances not really better what might be the advantage?? position in degrees cost!! 124

125 Resolution of position/speed encoders cost during the recent decades heterodyne interferometric encoders provide low resolution (slightly better than resolvers) - $ 500 resolution 125

126 Resolution of position/speed encoders during the recent decades cost heterodyne interferometric encoders provide low resolution (slightly better than resolvers) - estimated cost lower than high resolution optical encoders $ 500 resolution 126

127 Outline Introduction Drive Control Absolute and Differential Accuracy State of the Art Standard Encoders High Resolution Encoders Future Encoder Technologies Conclusions 127

128 Conclusions accuracy is decisive for position control resolution (or better : differential accuracy) is decisive for speed control in cascaded control structures speed control must be much faster than position control for encoders in digitally controlled drives resolution is much more important than accuracy actual encoders measure position and gain speed by derivation encoders measuring directly physical speed would be advantageous speed/position encoders still are the technical narrow gap in a drive without solving that problem new control schemes do not make sense with respect to a future increase of requirements investigations should be done 128

129 Questions?