Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
  • G08C19/00—Electric signal transmission systems
  • G08C19/38—Electric signal transmission systems using dynamo-electric devices
  • G08C19/46—Electric signal transmission systems using dynamo-electric devices of which both rotor and stator carry windings

Definitions

• This invention relates to a phase analog encoding system with compensation, used in connection with a resolver position transducer and utilized in servo control or monitoring applications.
• a resolver position transducer is a device which monitors the position of a rotatable shaft or a linearly displaceable member by measuring the angular displacement of the shaft or the linear displacement of the member with respect to a fixed reference point.
• the resolver when excited with the proper electrical input will output an electrical signal whose phase is related to the position of the shaft or member. •
• the position of the shaft or member is encoded in an electrical signal in an analog manner.
• the resolver position transducer is performing a servo-control function.
• phase shift errors inherent in a resolver position transducer are of particular importance in applications where the resolver is part of a phase analog encoding system.
• the phase analog encoding technique utilized in such systems involves applying reference signals to the resolver position transducer in the form of two sinusoidal signals displaced in time by 90 electrical degrees such as:
• VRl is the voltage across the equivalent of a stator sine winding
• VR2 is the voltage across the equivalent of a stator cosine winding
• K ] _ is a constant. Feedback from the resolver is taken by measuring the voltage across the equivalent of a resolver rotor winding, VFB. If VRl and VR2 are applied to the equivalent stator sine and cosine windings, the equivalent resolver rotor winding has a voltage of the form:
• VFB K 2 SIN ( ⁇ t + ⁇ + ⁇ ) (3)
• ⁇ is the mechanical displacement of a rotatable shaft or a linearly displaceable member
• ⁇ is the inherent electrical phase shift across the windings of the resolver position transducer
• K 2 is a constant. If the resolver position transducer is monitoring a rotatable shaft, the mechanical displacement ⁇ is an angular displacement. If the resolver position transducer is monitoring a linearly displaceable member, the mechanical displacement ⁇ is a linear displacement.
• the typical phase analog encoder operates by measuring the relative phase - —
• phase shift i.e. , phase shift
• the above encoding technique for measuring the mechanical displacement ⁇ will be accurate as long as ⁇ remains constant. Usually does not vary by more than one or two degress. As a result, the overall phase analog encoding system utilizing this technique is low cost, easy to apply and very effective for applications where an accuracy of one or two degrees is acceptable.
• One form involves mounting a temperature sensor in a network to compensate for the inherent electrical phase shift.
• the second form involves the use of an additional winding in the resolver position transducer and a separate encoding circuit which is used to monitor the electrical phase shift across the additional winding so that a • compensating signal can be generated which is then used to correct the primary encoding circuitry of the resolver position tranducer.
• the present invention overcomes disadvantages and objections associated with the prior art compensation for the electrical phase shift across the windings of a resolver position transducer.
• the disclosed invention is for an encoding technique wherein the inherent electrical phase shift across the windings of a resolver -Im ⁇
• position transducer (windings which are also part of the primary encoding circuit for determining the mechanical displacement of the position transducer) is measured in a time multiplexed fashion to correct for deviations due to all sources, including variations in temperature. It is to be understood that this invention can be applied to any sinusoidal position transducer. Where the term resolver transducer is used, it is intended to include: synchro, induction potentiometer resolver transmitter, control transfer transformer, differential control transformer ' and any other sinusoidal position transducer.
• this invention can be used in connection with a rotary resolver position transducer or a linear resolver position transducer.
• the mechanical displacement is an angular displacement and is equal to the rotor angle.
• the mechanical displacement is linear.
• a linear resolver has at least two windings which are the electrical equivalents of the stator windings, and at least one winding which is the electrical equivalent of the rotor winding.
• the invention utilizes a resolver position transducer in a phase analog encoding system wherein the total phase shift of the resolver transducer is determined by measuring the time interval between the zero crossing of the resolver sine reference and the zero crossing of the resolver feedback taken from the equivalent of a rotor winding of the resolver position transducer.
• the measured time interval between the zero crossings T is proportional to the sum of the mechanical displacement ⁇ and the electrical phase shift across the windings of the resolver -transducer :
• (1) and (3) is proportional to ( ⁇ + ⁇ )•
• This time interval can be used by a calculating means such as a computer or a microprocessor to determine ( ⁇ + ⁇ ), ⁇ - and many other useful variables by executing predetermined numerical manipulations.
• a calculating means such as a computer or a microprocessor to determine ( ⁇ + ⁇ ), ⁇ - and many other useful variables by executing predetermined numerical manipulations.
• the resolver transducer Periodically, at times selected by a calculating means and implemented by a reference switch in the resolver transducer encoding system, the resolver transducer is operated in a compensation mode. During the compensation mode, the resolver reference voltages (the voltages applied to the stator windings) are electronically switched and applied to the appropriate resolver stator windings. The appropriate windings are determined by the resolver encoding electronics to insure a large signal on the rotor windings.
• a resolver reference signal of K ⁇ SIN ⁇ t or - K ⁇ SIN ⁇ t is applied to one or the other of the resolver stator windings. This ensures that there will be the maximum possible output on the resolver rotor winding by applying a resolver reference voltage of the proper sign to the stator winding which has the most magnetic coupling for a given mechanical displacement ⁇ .
• a resolver reference voltage of the proper sign is applied to the stator winding which has the most magnetic coupling for a given mechanical displacement ⁇ .
• K ⁇ SIN ⁇ t is applied to the stator cosine winding
• the resolver transducer behaves " electrically like a transformer with the excited stator winding acting like a primary winding and the rotor winding acting like a secondary winding. As such, the voltage on the secondary winding will only differ in phase from the voltage on the primary winding by an amount equal to the inherent electrical phase shift across the resolver windings.
• the resolver encoder measures the time interval between the zero crossing of the resolver sine reference and the zero crossing of the resolver feedback signal
• the resulting time interval T is proportional to the inherent electrical phase shift across the windings of the resolver transducer ⁇ :
• the encoded value of ⁇ is then utilized by the calculating means to correct for any - 19 -
• the calculating means can determine the exact mechanical displacement ⁇ by subtracting the value of ⁇ from the measured quantity obtained during the normal measurement cycle, ( ⁇ + ⁇ ) .
• the duty cycle between the normal measurement cycle (measurement of ⁇ +ct ⁇ and the compensation cycle (measurement of only) is determined by the calculating means and can be either a strict function of time and/or a function of other variables as deemed appropriate to the application of the resolver encoding system.
• the phase analog encoding system with compensation for the phase shift error inherent in a resolver position transducer described by this invention has the additional feature of being self-calibrating.
• the encoding system can be operated in a calibration mode in which the inherent phase shift error in the encoding circuitry is measured. If the inherent phase shift error in the encoding circuitry y is taken into account, equations (4) and (5) , respectively become:
• T K 4 ( ⁇ + f) (5A)
• the calculating means uses the measured value of the inherent phase shift error in the encoding circuitry y to compensate for the . presence of this error during the normal measurement mode of operation and the compensation mode of operation.
• the phase analog encoding system described by this invention can be operated in a normal measurement mode, a compensation mode or a calibration mode of operation.
• the compensation mode of operation the inherent electrical phase shift of the resolver transducer is measured. This value is used during the normal measurement mode of operation to compensate the measurement of the mechanical displacement ⁇ .
• the calibration mode of operation the inherent phase shift error in the circuitry of the encoding means is measured. This measured phase shift error is used to compensate the measurements made during the compensation mode and the normal measurement mode of operation so that they are independent of any phase shift error inherent in the encoding circuitry.
• the inherent phase shift error in the circuitry of the encoding means ⁇ is measured in a time multiplexed fashion with the inherent electrical phase shift across the windings of the position transducer o and the sum ( ⁇ + ) of the mechanical displacement of the position transducer and the inherent, electrical phase shift across the windings of the position transducer ⁇ .
• the circuitry of the encoding means Periodically, at times selected by a calculating means and implemented by control electronics, the circuitry of the encoding means is operated in a calibration mode.
• the signal K ] _SIN ⁇ t is fed to the encoding circuitry instead of the feedback signal from the resolver transducer.
• This signal, K ⁇ SIN ⁇ t is the same as the reference signal that is being fed to the encoding circuitry.
• the measured time interval T between the zero crossings of these two signals is proportional to the inherent phase shift error in the encoding circuitry ⁇ :
• the time period representing the phase shift between an input signal of I ⁇ SIN ⁇ t and a reference signal of K ⁇ SIN ⁇ t should be zero.
• this phase shift may not be zero because of an inherent error within the encoding circuitry due to such things as the electronic drift of component values over time and changes in temperature. If a value for the inherent phase shift error in the encoding circuitry Y other than zero is measured, this value can be utilized by the calculating means to compensate the measurements made during the - t3 -
• the duty cycle between the normal measurement cycle (measurement of ⁇ + ⁇ ), the compensation cycle (measurement of ⁇ only) and the calibration cycle (measurement of y only) is determined by the calculating means and can be either a strict function of time and/or a function of other variables deemed to be appropriate to the application of the resolver encoding system.
• the general theory for the measurement of the inherent phase shift error in the encoding circuitry ⁇ is the same as for the measurement of the inherent phase shift error across the resolver windings ⁇ except that only K ⁇ SIN ⁇ t is needed as a reference signal and can be used by the encoding means whereas in the meansurement of ⁇ , K ⁇ SINat or - K ⁇ SI at is applied to either the stator sine winding or the stator cosine winding and the rotor feedback signal is used by the encoding means.
• FIGURE 1 shows a schematic of a rotary resolver position transducer with the reference signals applied to the stator windings and the feedback signal taken from the rotor winding in the phase analog form.
• FIGURE 2 shows a typical phase analog encoding system using a rotary resolver transducer wherein the relative phase shift between the reference sine winding and the feedback rotor winding is computed by a time interval circuit.
• FIGURE 3 shows a typical reference frequency generator where the value of the divider determines the resolution of the encoding system.
• FIGURE 4 shows the timing diagram for the encoding of the phase shift in the time interval.
• FIGURE 5 shows a block diagram of the resolver based phase analog encoding system described by this invention.
• FIGURE 6 shows the resolver based phase analog encoding system described by this invention as applied to a rotary resolver position transducer.
• FIGURE 7 shows the logic utilized in connection with a rotary resolver position transducer to determine which reference signal polarity and which stator winding should be excited during the compensation cycle in order to guarantee a rotor signal of sufficient magnitude to make a valid reading of the inherent electrical phase shift across the resolver windings regardless of the rotor position.
• FIGURE 8 shows an example of the control electronics which implements the control signal from the calculating means to determine when the resolver encoding means operates in the calibration mode.
• the invention is used in connection with a rotary resolver position transducer.
• the mechanical displacement ⁇ in a rotary resolver position transducer is the mechanical rotor angle representing the angular displacement of the rotor with respect to the stator windings.
• a rotary resolver transducer 2 is basically an angle transducer and is well* known in the art.
• a rotary resolver transducer includes a rotor 5 having one or more sets of spaced apart windings and a stator 6 having two or more sets of spaced apart windings. These windings are called a rotor winding 10, and stator windings 20, respectively.
• the resolver stator sine winding 21 is excited by a reference signal 25 of the form KnSIN ⁇ t and the resolver stator cosine winding 22 is excited by a reference signal 26 of the form K ⁇ OS ⁇ t.
• the signal 27 on the feedback rotor winding 10 takes the form K 2 SIN ( ⁇ t + ⁇ + ⁇ ) where the mechanical displacement ⁇ is the mechanical rotor angle measuring the position of the rotor 5 with respect to the stator windings 20 and ⁇ is the inherent electrical phase shift across the resolver transducer 2.
• FIGURE 2 shows a typical phase analog encoding system consisting of a resolver transducer 2, as shown in FIGURE 1, a resolver encoding means and a resolver reference means, described hereinafter.
• a typical resolver encoding means consists of two zero crossing detectors 41 and 42 and a digital counter 43.
• the input to the first zero crossing detector 41 is from the sine reference signal 25, and the output is connected to the start switch of the digital counter 43.
• the input to the second zero crossing detector 42 is from the feedback rotor winding 10 and the output is connected to the stop switch of the digital counter 43.
• the encoding system operates by starting the digital counter 43 when the first zero crossing detector 41 determines that the sine reference signal 25 crosses zero voltage.
• the digital counter 43 then counts the reference frequency 44 until a zero voltage crossing on the - n-
• the feedback rotor winding 10 is detected by the second zero crossing detector 42.
• the digital counter 43 is then stopped.
• the accumulated value 28 in the digital counter 43 is equal to the sum of the mechanical rotor angle and the inherent electrical phase shift of the resolver transducer ( ⁇ + ) .
• the resolution of the encoding system is determined by the reference frequency 44 which the digital counter 43 counts.
• the reference frequency 44 is generated by the resolver reference means which also generates the reference signals 25 and 26 which are applied to the resolver stator windings 20.
• a typical resolver reference means as shown in FIGURE 2, consists of a reference signal generator 51 and two amplifiers 47 and 48 which are used to increase the strength of the reference signals 25 and 26 before they are applied to the resolver stator windings 20.
• the reference signal generator 51 as shown in FIGURE 3, consists of an oscillator 52, a divider 53 and a 90° phase shifter 54.
• the oscillator 52 generates the reference frequency 44 that is counted by the digital counter 43.
• the output of the oscillator 52 is divided by a value N in a divider - ⁇ -
• the value of N can be pre-set or can be varied by the calculating means.
• the reference frequency 44 is equal to N times the frequency of the reference signals 25 or 26 applied to the stator windings 20. The larger the value of N, the greater the resolution of the encoding system.
• the output of divider 53 is fed through amplifier 48 before being applied to the stator sine winding 21.
• the output of divider 52 must be fed through a 90° phase shifter 54. This phase shifted reference signal is then amplified by amplifier 47 before being applied to the stator cosine winding 22.
• FIGURE 4 The timing diagram for the phase analog encoding system of FIGURE 2 is shown in FIGURE 4.
• the reference signal 25 to the stator sine winding 21 is depicted by waveform 71.
• the voltage on the feedback rotor winding 10 is depicted by waveform 74.
• Waveforms 72 and 75 show the output of the first zero crossing detector 41 and the second zero crossing detector 42, respectively.
• Waveform 73 is the output 28 of the digital counter 43.
• the digital counter 43 continues to count the reference frequency 44 until it receives a signal to stop.
• the second zero crossing detector 42 is activated, as indicated by waveform 75 and this sends a stop counting signal to the digital counter 43.
• the time interval that the digital counter 43 has counted is equal to the sum of the mechanical rotor angle and the inherent electrical phase shift of the resolver transducer ( ⁇ + ).
• the digital counter 43 is reset after the phase angle number is read in preparation for the next start/stop sequence.
• the present invention discloses a novel- and unique system for compensating for the inherent electrical phase shift error of a resolver position transducer in a time multiplexed fashion. Additionally, the invention has a self- calibrating feature.
• FIGURE 5 shows the overall phase analog encoding system with compensation as described by the invention.
• the resolver reference means 50 generates reference signals 25 and 26 which are fed to the resolver transducer 2 and reference signal 44 which is used by the digital counter 43 in the resolver encoding means 40.
• the rotor feedback signal 27 from the resolver transducer 2 is used by the resolver encoding means 40 along with the stator sine reference signal 25 and the reference signal 44 to measure the sum of the mechanical displacement ⁇ and the inherent electrical phase shift across the resolver ⁇ .
• the calculating means 80 uses the output 28 from the encoding means 40 along with
• the calculating means 80 also determines through 0 control signal 82 which reference signals 25 and 26 of the resolver reference means 50 are applied to the resolver transducer 2.
• Control signal 82 determines whether the entire encoding system is measuring the sum ( ⁇ +
• control signal 82 has the encoding system in the normal measurement mode of operation the output 28
• 25 28 of the resolver encoding means 40 is the inherent electrical phase shift of the resolver, ⁇ *
• This measured value of ⁇ is then compared with an old value of ⁇ by the calculating 30 means 80 and a new value of is calculated.
• the new value of is then used by the calculating means 80 along with the output 28 of the resolver encoding means 40 under the normal measurement mode of operation to obtain a value for the mechanical displacement ⁇ , which is independent of the inherent electrical phase shift of the resolver ⁇ .
• the calculating means 80 through control signal 119, also determines whether the entire encoding system is operating in the calibration mode or in the other modes of operation, i.e. , the normal meansurement mode or the compensation mode. As will be described in detail infra, control signal 119 takes priority over control signal 82.
• FIGURE 6 shows the invention depicted by the block diagram in FIGURE 5 as applied to a rotary resolver position transducer.
• the calculating means 80 in the preferred embodiment is a microprocessor unit. However, it does not have to be so limited. It can be any type of computer, arithimetic logic unit, or appropriate control circuitry and software which is capable of: processing the output 28 of the resolver encoding means 40; generating a control signal 82 for the resolver reference means which determines whether the encoding system is in the normal measurement mode of operation or in the compensation mode of operation; and generating a control signal 119 for the resolver encoding means -2&-
• the encoding system cannot be in all three modes of operation at once. It can only be in one mode of operation at a time. That is one of the advantages of this invention. It utilizes the same physical measuring circuit in a time sharing fashion to calculate the mechanical displacement , the inherent electrical phase shift of the resolver transducer ⁇ , and the inherent phase shift across the circuitry of the encoding means )f .
• the duty cycle between the measurement cycle (measurement of ⁇ + ⁇ ) and the compensation cycle (measurement of ⁇ only) is determined by the software of the microprocessor unit and can be either a strict function of time and/or a function of other variables deemed to be appropriate, depending on the specific use of the encoding system. If the duty cycle is a strict function of time, the measurement cycle occurs on the order of 1000 times a second and the compenstaion cycle occurs on the order of once every second.
• the duty cycle between the combination of the normal measurement cycle (measurement of ⁇ + ⁇ ), the compensation cycle (measurement of ⁇ only) , and the calibration cycle (measurement of t only) is determined by the microprocessor and the control circuitry.
• Reference switch 87 which implements control signal 82, is shown in FIGURE 7. In the normal measurement mode of operation, switch 95 is closed connecting the sine reference signal 25 to the stator sine winding 21 and switch 96 is closed connecting the cosine reference signal 26 to the stator cosine winding 22.
• the reference signal is applied to either the stator sine winding 21 or the stator cosine winding 22 depending upon the position of the resolver rotor 5 (i.e./ the mechanical rotor angle of the resolver ⁇ ) .
• the reference signal 25, K ] _SIN ⁇ t is put through a signal inverter 88.
• the reason for applying the different reference signal (either K ⁇ I ⁇ t or -K ⁇ SIN t) to either the stator sine winding 21 or the stator cosine winding 22 is to ensure-that there is a large signal output on the resolver rotor winding 10 and that the measurement of ⁇ will be valid * independent of the rotor position ⁇ .
• the microprocessor unit determines what the value of ⁇ is at any given point in time during the normal measurement cycle. This value of ⁇ is then encoded into a binary number which determines which switch is closed and correspondingly which configuration of reference voltages is applied to the resolver stator windings.
• the table in FIGURE 7 shows which binary number corresponds to which range of values of ⁇ and what the reference switch position will be for that binary number.
• FIGURE 8 shows an example of the control electronics 120 necessary to implement control signal 119.
• the control electronics 120 is composed of an electronic switch 121. -_35-
• Control electronics 120 can be more elaborate, although it does not have to be. It can be as simple as a relay that moves electronic switch 121 from pole 125 to 126 when a control signal 119 is received.
• electronic switch 121 In the normal, measurement mode of operation, or in the compensation mode of operation, electronic switch 121 is connected to pole 125 such that the feedback signal 27 is inputted into the second zero crossing detector 42 of the resolver encoding means 40. In the calibration mode of operation, the electronic switch 121 is connected to pole 126 such that the sine reference signal 25 is inputted into the second zero crossing detector 42 of the resolver encoding means 40.
• the resolver encoding means measures the electrical phase shift between the signal at pole 126, K ⁇ SIN ⁇ t, and the reference signal, K ⁇ SIN ⁇ t, inputted into the first zero crossing detector 41. If the resolver encoding means is working perfectly, the output 28 of the resolver encoding means 40 will be zero since there is no phase shift between two-signals of the form K ⁇ SIN ⁇ t. If, however, the output 28 of the resolver encoding means 40 is a value other than zero, this value can be utliized by the calculating means 80 to compensate for this measured phase shift error when the encoding system is operating in the normal, measurement mode of operation or the compensation mode of operation.
• Calculating means 80 sends a control signal 119 to the control electronics 120 to determine whether the entire encoding system is operating in the calibration mode or in the other modes of operation, i.e. , the normal measurement mode or the compensation mode.
• Control signal 119 takes priority over control signal 82 since electronic switch 121 must be connected to pole
• control signal 82 can have an effect on the resolver encoding means 40.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Transmission And Conversion Of Sensor Element Output (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

Family

ID=24238760

Family Applications (1)

Country Status (4)

Family Cites Families (7)

• 1984
  • 1984-12-07 CA CA000469585A patent/CA1217866A/en not_active Expired
  • 1984-12-10 DE DE8585900395T patent/DE3485632D1/de not_active Expired - Fee Related
  • 1984-12-10 WO PCT/US1984/002019 patent/WO1985002702A1/en active IP Right Grant
  • 1984-12-10 EP EP19850900395 patent/EP0165304B1/de not_active Expired

Also Published As

Similar Documents

Legal Events