Resolver-to-Digital Module
Contents
1. VssGNDVdd Fig 6 Schematic diagram of the Power supply circuit zt l R D Integrated Circuits The core of the R D modul is created by two monolithic ICs the reference generator unit AD25S99 which provides a constant amplitude sinusoidal excitation for the resolver and the 12 bit R D converter AD2S90 which translates differential sine and cosine signals generated by the re solver into a digital information You can see circuit configuration of these two ICs in Figure 7 Gerstner Lab Prague Jan 2003 page 10 17 Resolver to Digital Module Freq Apra em Ven exc n _ excl SIN Hi AD2S99 exc GNDI DGnd AGnd GND COS Hi cos ne ne ne U2 AD2589 LOS Vdd R3 1G ND 100k Gz 2 Vdd Jn COS LO COS Hi Di J Vss GNDI GND SIN Hi DIE SIN Lo GND 11 2590 Fig 7 R D Converter AD2S90 and Oscillator AD2S99 configuration AD2S90 R D Converter The AD2S90 is a 12 bit resolution monolithic resolver to digital converter It provides a complete solution for digitizing resolver signals without using external components To get position angle 9 in digital form both sine and cosine channel signals must be sent to the R D converter for decod ing This chip provides not only absolute position data output in serial form but also standard A Quad B format signals The absolute position data output gives additional useful information The serial form of the digital position data i2. F Sin Output eg Secondary S Tate Lon ansiota HI E i OS E D GEA Fig 4 Traditional brushless resolver with wound rotor and rotary transformer Resolver to Digital Conversion While resolvers were originally developed for military and aerospace applications in recent years industrial automation has shown more interest in these rugged and precise absolute position transducers Nevertheless the expansion of the use of resolvers was often limited by the fact that the signal conversion required cumbersome circuitry and automated resolver production was diffi cult Now however inexpensive and easy to implement monolithic ICs that perform complete resolver to digital conversion are available These R D converters give an absolute or incremental output with a resolution of up to 65 536 counts per revolution A typical two chip solution is shown in Fig 5 Resolver Excitation Oscillator AD2S99 Digital et cde AD2S90 Fig 5 Simple R D conversion using two monolythic ICs The resolver signals are low bandwidth amplitude modulated sine waves Since these sine wave signals contain only a single frequency component rather than the virtually infinite frequency spec trum of an optical encoder s square wave signals they are inherently much more immune to the high frequency noise generated by PWM motor drives and other industrial machinery Gerstner Lab Prague Jan 2003 Resolver to Digital Module pa
3. for standard Quad Encoder or Serial digital communication but are presented AD2S90 output pins Add OUT GND Fig 14 Add Output Connector The analog velocity output VEL is scaled to produce 150 rps V DC 15 The sense is positive for increasing angular rotation I O Resolver connector J3 is shown in Fig 15 Resolver Fig 15 Resolver I O Connector The resolver shall be connected to the module according to Fig 16 2 2 Qo eoQ Excitation Resolver Fig 16 Resolver connection to the R D module 6 wire cable with a common shield was used in our lab for a signal transmission from an auxiliary BNC connectror box to the R D module connector J3 The following table assignment is specific only for this application Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 15 17 SIN Hi Blue SIN Lo COSHI brown COS Lo black EXC Hi EXC Lo Gerstner Lab Prague Jan 2003 page 16 17 Resolver to Digital Module Conclusions The main purpose of this report is to describe the Resolver to Digital module This modul is an interlink between the resolver analog measurement of speed and position and the Digital signal processor digital control of frequency converter Used control board with Motorola DSP56F805 is equipped with a peripheral circuit assigned to process quadrature signals from an incremental encoder DC motor in our lab used as a variable load has a resolver integra
4. Resolver to Digital Module Annotation Resolver technology has been used in the industrial environment tor many years This technology still provides the best angular position transducer available in terms of ruggedness reliability and resolution Re solver Digital Module provides excitation to the resolver and translates the returned angular analogue information into a digital form for motion control applications using motors with resolver feedback The digital an gular position output information is available in two forms As a serial bi nary output providing the absolute position and as two quadrature sig nals A and B and the Z zero pulse emulating an incremental encoder Author Petr Kadanik Gerstner 7 mu Rockwell Automation page 2 17 Content INTRODUCTION WHAT IS A RESOLVER RESOLVER SIGNAL FORMAT BRUSHLESS RESOLVERS RESOLVER TO DIGITAL CONVERSION TECHNICAL SUMMARY KEY FEATURES POWER SUPPLY R D INTEGRATED CIRCUITS AD2S90 R D CONVERTER AD2S99 PROGRAMMABLE OSCILLATOR OSCILLATOR OUTPUT STAGE CONNECTORS CONCLUSIONS REFERENCES APPENDIX Gerstner Lab Prague Jan 2003 Resolver to Digital Module oO Un RR U 10 11 12 12 16 17 17 Resolver to Digital Module page 3 17 Introduction Flexible motor control is unthinkable without precise information about the position of the shaft For this purpose different types of shaft angle sensors are u
5. e which outlines the main components and the con nectors on printed circuit board PCB Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 13 17 Power LED Power LED Input Power SUDRA Connectors 4 dt O Frequency Select S Jumpers d Resolver I O Connector T E 7 AD2S99 Digital Output SCH nectorsPower LED Excitation Output bypass jumpers Fig 11 R D Module board layout The excitation frequency for the resolver can be easy selected by jumpers setting on JP1 header according to the following table BEEN o BEES o 5H o 1 o i 1 1 o 1 oO o i Jumper JP2 has to be closed if you don t want to set up intermediate frequency value See AD2S99 DataSheet in Appendix B for more details The function of jumpers JP3 and JP4 is understandable from Fig 10 They can bypass operational amplifiers in excitation output signal buffer circuit Signal gain is 1 when JP3 and JPA are closed Jumper JP3 is bypassing signal EXC Hi and jumper JP4 is bypassing signal EXC Lo Output Encoder connector J4 is shown in Fig 12 Encoder OUT Fig 12 Encoder Output Connector Output Serial connector J5 is shown in Fig 13 Gerstner Lab Prague Jan 2003 page 14 17 Resolver to Digital Module rial OUT GND s e Fig 13 Serial Output Connector Output connector J signed Add is shown in Fig 14 This connector contents signals not used
6. ge 17 The resolver to digital converter performs two basic functions demodulation of the resolver for mat signals to remove the carrier and angle determination to provide a digital representation of the rotor angle The most popular method of pertorming these functions is called ratiometric tracking conversion Since the resolver secondary signals represent the sine and cosine of the ro tor angle the ratio of the signal amplitudes is the tangent of the rotor angle Thus the rotor angle is the arc tangent of the sine signal divided by the cosine signal sind V arctan cos arctan The ratiometric tracking converter performs an implicit arc tangent calculation on the ratio of the resolver signals by forcing a counter to track the position of the resolver This implicit arc tangent calculation is based on the trigonometric identity sin 8 sin cos cos sin This equation says that the sine of the difference between two angles can be calculated by cross multiplying the sine and cosine of the two angles and subtracting the results Further as long as the difference between the two angles is relatively small 6 630 the approximation sin 8 5 6 may also be used further simplifying the equation Thus if the two angles within 30 of each other the difference between the angles can be calculated using the cross mul tiplication shown above In the R D converter this equation is im
7. ice with bearings and shaft be used in all but the crudest applications Since encoders are typically connected to a shaft having its own bearings the user must pay for the second set of high quality bearings in the transducer as well as a flexible coupling to connect the two shafts In many applications especially brushless servo motor commutation or flux vector control of AC induction motors the additional length of the optical encoder s shaft bearings and coupling 15 too great and the optical encoder cannot be used On the other hand inductive transducers such as resolvers are intrinsically absolute and require no semiconductors on the transducer itself the raw output signal can be transmitted over dis tances of more than 100 meters In addition since they consist primarily of copper and steel re solvers are virtually insensitive to temperature over a wide range Because no sensitive electronics or optics are employed resolvers are often supplied in an unhoused also called frameless or pancake configuration and can be mounted directly to the shaft whose position is to be mea sured Cost and length savings are realized by the user since no shaft to shaft coupling or extra bearings are required What is a resolver A resolver is a position sensor or transducer which measures the instantaneous angular position of the rotating shaft to which it is attached Resolvers and their close cousins synchros have been in use since before Wor
8. ings or a rotating trans former to couple signals into the primary Like all transformers a resolver requires an AC carrier or reference signal sometimes also called the excitation to be applied to its primary The amplitude of this reference signal is then modu lated by the sine and cosine of the rotor angle to produce the output signals on the two seconda ries For best performance the reference signal should be a sine wave In any transformer there is a value which relates the output voltage produced by the secondary to that fed into the primary For resolvers this quantity is called the transformation ratio or TR and is specified at the point of maximum coupling between primary and secondary For industrial resolvers the defacto standard transformation ratio is 0 5 which means that the maximum voltage produced by either secondary is half the amplitude of the reference signal If we define the reference voltage Ve then the voltages on the secondaries are given by the follo wing equations Sine Secondary Vs Ve TR sin Cosine Secondary Me TR where 6 1 the mechanical angle of the rotor Resolver Signal Format If we excite the primary Ve with the recommended sinusoidal reference signal as shown below the secondary voltages are also sinusoidal at the same frequency and nominally in phase with the reference Their amplitude is proportional to the amplitude of the reference the transformation ratio TR and
9. ld War Il in military applications such as measuring and controlling the angle of gun turrets on tanks and warships Resolvers are typically built like small motors with a rotor Gerstner Lab Prague Jan 2003 page 4 17 Resolver to Digital Module attached to the shaft whose position is to be measured and a stator stationary part which pro duces the output signals The word resolver is a generic term for such devices derived from the fact that at their most basic level they operate by resolving the mechanical angle of their rotor into its orthogonal or Cartesian X and Y components From a geometric perspective the relationship between the rotor angle 9 and its X and Y components is that of a right triangle sinO cosO Fig 1 Resolving an Angle into its Components Fundamentally then all resolvers produce signals proportional to the sine and cosine of their rotor angle Since every angle has a unique combination of sine and cosine values a resolver provides absolute position information within one revolution 360 of its rotor This absolute as opposed to incremental position capability is one of the resolver s main advantages over in cremental encoders Electrically a traditional resolver is a transformer in which the coupling between the primary and the secondaries varies as the sine and cosine of the rotor angle A resolver has its primary on the rotor and its secondaries in the stator necessitating brushes and slip r
10. ltages in the two stator windings whose amplitudes are dependent on the rotational angle of the rotor To provide sine and cosine signals the two secondaries are wound in space quadrature 90 physical degrees apart in the stator Electrical energy has to be supplied to the rotor to generate its AC magnetic field However as the rotor must be able to rotate freely it is not possible to use wires The use of slip rings is also not recommended because they are subject to wear generate signal noise and compromise the mechanical ruggedness of the resolver The brushless resolvers therefore use a rotary coupling transformer to transfer energy from the stator to the rotor The primary of this rotary transformer is built into the stator The secondary is mounted on the rotor and connected directly to the resolver primary Because of the energy lost in energizing this two stage transformer basically two transformers in series many turns of wire are required to generate usable output signal amplitudes The large number of turns means that the Gerstner Lab Prague Jan 2003 page 6 17 Resolver to Digital Module resolver is a relatively high impedance device limiting its use at high excitation frequencies or rotational speeds Because the resolver has a wound rotor its maximum speed is limited since the windings tend to fly out of the rotor due to centrifugal force Typical maximum speeds are 10 000 RPM or less Fic 2 27 Transformer TT
11. m 8 2 5 amp 4 C 2 gt oux C7 O Vdd GND CFI 1MO e Vss GND Vdd E O Vss DIR NM exc wl of ml o GND E gt Al al OI m T Vdd 5V Vss 5V 5 Freq output selection ISELIISH2 2kHz Vss Vss SkHz Vss IGND 10kHz GND Vss 20kHz GNH GND 8 7 6 5 4 3 2 1 Resolver I O J4 A 1 16 18 B ES 1 e NM 3 Vel 2 7 DIR 4 ClkOut 3 6 5 4 5 GND Encoder OUT ds Add OUT 3 GND 2 1 Title ner J7 GND Resolver to Digital Board TestPoints PWR Date 15 Jan 2003 D Protel Design Resolver t Drawn B 3 2 O Vss Size Number Revision 1 O Vdd A4 1 0 Selection 2 2 7 U C y J U d A LL UU 04
12. o pulse emulating an incremental en coder These signals are available on the quadrature encoder connector pins The encoder emulated outputs continuously produce signals equivalent to a 1024 line encoder Key features e 12 bit serial absolute position e Ax1024 lines incremental encoder emulation e Differential inputs for resolver signals e Internal oscillator providing sinusoidal excitation with an arbitrary frequency 2 20kHz e External power supply 7 25V DC 100mA is required Power supply The printed circuit board requires 7 25V DC 100mA power supply Input power circuit deli vers 5V DC to an isolated DC DC converter providing bipolar 5V DC voltage output galvani cally isolated from an input power supply A green LED indicates power applied to the modul Schematic diagram of power supply stage is shown in Fig 6 The main power input is either through connector J1 2 pin connector or connector J2 2 1 mm coax power jack Vss is net label for 5V DC voltage and is a net label for 5V DC voltage GND is a common ground for both digital and analog signals galvanically isolated from an input power supply GND PWR Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 9 17 12V PWK BZA83V008 2 25 000UFI16V sh 100nF JACK PWR EJ 78 05 GND GND PWR 1O00nF 100uF 10VlM 2k5 KK 3 MK S4 2M263V LEL GNL PWR i SYNCin c SYNCout B C7 enp CF 1 1m CF 1 110
13. plemented using multiplying D A converters to multiply the resolver signals proportional to sin and cos by the cosine and sine of the digital angle 6 which is the output of the converter The results are subtracted demodulated by multiplying by the reference signal and filtered to give a DC signal proportional to the difference or error between the resolver angle and the digital angle The digital angle stored in the counter is then incremented or decremented using a voltage controlled oscillator until this error is zero at which point 5 0 the digital angle output of the converter is equal to the resolver angle This incrementing and decrementing of the digital angle causes it to track the resolver angle 0 hence the name of this type of converter Gerstner Lab Prague Jan 2003 page 8 17 Resolver to Digital Module Technical Summary Resolver to digital interface module offers an effective solution for motion control applications using motors with resolver feedback It provides the resolver excitation and translates the returned angular analogue information into a digital form The digital angular position output information is available in two forms As a serial binary output providing the absolute position This output is available on the serial peripheral connector SPI pins The absolute position has 12 bits resolution pro viding 4096 values per rotation As 2 quadrature signals A and B and a Z zer
14. s The synchronous ref erence output compensates for temperature and cabling dependent phase shifts and eliminates the need for external preset phase compensation circuits The excitation frequency is easily programmed to 2 kHz 5 kHz 10 kHz or 20 kHz by using the frequency select pins Intermediate frequencies are available by adding an external resistor PUSH EXC PULL STAGE Ke T FREQUENCY SINE WAVE E SELECT GENERATOR SEL2 SYNREF SYNCHRONOUS PHASE _ ft B SIN COS TRANSDUCER Fig 9 Functional block diagram of AD2S99 Functional block diagram is shown in Fig 9 Please see Appendix B for more details about AD2599 Gerstner Lab Prague Jan 2003 page 12 17 Resolver to Digital Module Oscillator output stage The output of the 2599 oscillator consists of two sinusoidal signals EXC and EXC EXC is 180 phase advanced with respect to EXC With low impedance transducers it may be necessary to increase the output current drive of the AD2S99 In such an instance an external buffer amplifier can be used to provide gain as needed and additional current drive for the excitation output either EXC or EXC of the AD2S99 providing a single ended drive to the transducer Refer to Fig 10 for a buffer configurations GND Fig 10 Circuit scheme for an excitation signal gain adjustment I O Connectors Fig 11 presents a top view of the modul
15. s especially suitable for long distance data transmission All the input output signals are TTL logic compatible Functional block diagram is shown in Fig 8 Please see Appendix B for more details about AD2590 Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 11 17 REF SIN C bk SIN 0 SIN LOC HIGH ACCURACY P S D AND VEL ANGLE SIN COS FREQUENCY COS SHAPING gt MULTIPLIER COSLOO DIGITAL AMPLIFIER ANGLE UID CLKOUT NMC O HIGH UP DOWN A DECODE COUNTER DYNAMIC B LOGIC RANGE V C O Dip CS LATCH DATA S SERIAL INTERFACE DATA SERIAL INTERFACE Fig 8 Functional block diagram of AD2S90 The AD2S90 emulates a 1024 line encoder Relating this to converter resolution means one revo lution produces 1025 A B pulses B leads A for increasing angular rotation The addition of the DIR output negates the need for external A and B direction decode logic DIR is HI for increasing angular rotation The north marker NM pulse is generated as the absolute angular position pas ses through zero AD2S99 Programmable Oscillator The AD2S99 programmable sinusoidal oscillator provides sine wave excitation for resolvers and a wide variety of AC transducers The AD2S99 also provides a synchronous reference output sig nal 3 V p p square wave that is phase locked to its SIN and COS inputs In an application the SIN and COS inputs are connected to the transducer s secondary winding
16. sed often built into the driving mo tors On the basis of their physical design these angular transducers can be classified into two main groups e Optical A phototransistor or other light sensitive electronic device counts lines on a transparent disk mounted to the rotating shaft The most common of these devices are incremental and absolute encoders e Inductive Built like small electrical motors where inductive coupling between a rotating part the rotor and a stationary part the stator generates signals indicating shaft position Resolvers and synchros are the most common devices Optical transducers especially incremental encoders have found wide application because their digital outputs can be easily processed by both discrete logic and microprocessors Nevertheless optical transducers have a number of characteristics that make them less than optimal for many applications The built in semiconductors used to amplify and format the digital output signals are sensitive to temperature and the LED light sources commonly employed are susceptible to aging Furthermore applications that require an absolute output signal require absolute encoders which are much more complicated and therefore expensive From a purely practical standpoint the precise concentricity between the encoder disk and the sensors required to maintain accuracy as well as the mere presence of optical devices in an industrial environment dictate that a fully enclosed dev
17. ted on its shaft The applying of R D module was therefore a natural and the easiest option how to measure motor speed with out replacing the resolver by the incremental encoder Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 17 17 References e Resolver to digital Interface Module RDIM16 User Manual Technosoft 2001 e Circuit Applications of the AD2S90 Resolver to Digital Converter Analog Devices Applica tion Note AN 230 e Digital Resolver Integration Analog Devices Application Note AN 234 e New Absolute Inductive Transducer for Brushless Servomotors Technical Paper Ad motec Inc 1995 Appendix All schematics are included in this appendix For schematics and PCB design was used software package Protel 99 This appendix includes also datasheets and technical specifications of compo nents implemented in R D module design Gerstner Lab Prague Jan 2003 Jl Di CT4M7 10V Tantal Vdd JP1 GND C8 Ci2 CIO C14 100nF 4 7uF 100nF 4 7uF 1 Vdd oa 4 0 0 Vss Jp gs 22 BZX83V0082 7 de Rf Freq Selection GND 1 ON 20 1000uF 16V Freq Aprox O Vss 100nF a md 100nF 4 7uF 100nF 4 7uF C13 11 15 4 18 78M05 C17 C18 C19 SIN Hi 5 17 100nF 100nF 100nF Vdd f T GND GND COS Hi 7 15 8 14 100nF 100uF LOVM 9 10 11 P 13 MKS4 2M2 63V 100 Q c X O Vdd R3 14 po GND 100k
18. the sine or cosine of the mechanical angle of the rotor While it is helpful to know how the resolver signals appear as functions of time since that is what one sees when one looks at them with an oscilloscope it is often more convenient to work with the Gerstner Lab Prague Jan 2003 Resolver to Digital Module page 5 17 envelope amplitude at the reference frequency of the signals with respect to rotor position If the rotor of the resolver is turned at a rate such that it makes one complete revolution in the time of 10 cycles of the excitation frequency speeds this high are very difficult and cause other problems in practice but are useful tor understanding the envelope of the secondary signals can be clearly seen Shown below Fig 2 is the envelope of the sine secondary signal with respect to rotor posi tion Gol 180 2 0 50 Fig 2 Modulation Envelope of Sine Secondary Signal The process of removing the carrier signal leaving just the envelope is called demodulation and is performed by the Resolver to Digital R D converter The demodulated sine and cosine resolver signals are shown in Fig 3 Sine d Cosine D 90 180 270 360 Fig 3 Demodulated Resolver Secondary Signals Brushless Resolvers The traditional brushless resolver consists of a wound rotor and stator as shown below Fig 4 The windings on the rotor generate an AC magnetic field with a sinusoidal distribution This field induces vo
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