The present invention relates to an integrated torque and position sensor for detecting the relative rotational angular displacement between two rotatable shafts joined by a torsion bar and for detecting the angular position of a rotatable shaft. The present invention also provides a method of calibrating and calculating the angular position of shaft.
The need to measure both the torque and the angular position of a steering shaft is important to automotive applications utilizing an electric power steering system (EPS). A number of standalone sensors have been developed related to either determining torque or calculating the angular position of a steering wheel. Generally, it is necessary to calculate the torque in order to determine the amount of electrical assist to apply when a driver turns a steering wheel. In determining torque, the driver typically turns the steering wheel which is connected to an input shaft. The input shaft is coupled to an output shaft which is connected to a steering mechanism. The input and output shafts are generally coupled together with a torsion bar and the torsion bar allows for relative rotation between the shafts. The input shaft may rotate with respect to the output shaft by a predetermined number of degrees, e.g. +/−12 degrees. An example of a torque sensor is disclosed in U.S. Patent Application Publication No. 2004/0250631 filed on Jul. 13, 2004 which is assigned to the assignee of the present invention and is hereby incorporated as a reference. An example of a position sensor is disclosed in U.S. Pat. No. 6,720,763 which is assigned to the assignee of the present invention and is hereby incorporated as a reference.
Position sensors are used for determining the angular position of the shaft as a user turns a steering wheel. Examples of position sensors are disclosed in U.S. Pat. No. 5,930,905 (the '905 patent) to Zabler et al., and in U.S. Pat. No. 6,630,823 (the '823 patent) to Tateishi et al. The '905 patent discloses a gear having a plurality of teeth coupled to a shaft. The teeth engage a plurality of additional teeth disposed on a second gear and a third gear. A pair of absolute sensors are positioned in proximity to the second gear and the third gear for generating an output that corresponds to the angular positions of the gears. As long as the number of teeth on each of the gears are known, it is possible to calculate the angular position of the shaft based on the outputs of the absolute sensors.
The '823 patent discloses a gear having a plurality of teeth coupled to a shaft. As the shaft rotates, the teeth on the gear engages with additional gear teeth disposed on a second gear. A bevel gear disposed on a different plane from the second gear engages a change gear. A first sensing element is positioned in proximity with the change gear for outputting a first detection signal which repeats continuously. A screw is positioned through the change gear and rotates with the change gear as the change gear rotates. A driven body is coupled with the screw and is axially displaced in response to rotating the change gear. A second sensing element is positioned in proximity to the driven body and outputs a second detection signal which gradually increases or decreases. A detection circuit determines the angular position of the shaft based on the first and the second detection circuits.
Although these prior art position sensors are useful, an opportunity exists for a position sensor that minimizes the number of gear teeth disposed on a gear while providing the angle position of the shaft with accuracy. By reducing the number of gear teeth on a gear, the sensor is not susceptible to losing accuracy as a result of the teeth wearing down over time. Additionally, an opportunity exists for combining the torque and position sensing capabilities into an integrated sensor to occupy less package space in a vehicle. Finally, by combining the functionality of a sensor which calculates both the torque and angular position of a shaft, common parts may be utilized within the sensor for providing additional cost savings.
It is the object of the present invention to provide an integrated torque and position sensor for measuring the relative rotation between an input and an output shaft and for measuring the angular position of the output shaft. The integrated torque and position sensor includes a support housing that supports the output shaft about an axis and an input shaft that is axially aligned with the output shaft for rotation about an axis. A torsion bar interconnects the input shaft and the output shaft for allowing relative rotation between the shafts in response to a torque being applied to the input shaft. A wheel is coupled to the output shaft for rotation therewith. A torque sensing mechanism is disposed about the shafts for measuring the relative rotation between the input and the output shaft. An incremental sensing mechanism generates an incremental output which is indicative of the angular position of the output shaft and a segment sensing mechanism provides a segment output indicative of the revolution in which the output shaft is disposed. A sensor casing is supported by the support housing and the sensor casing supports portions of the torque, incremental, and segment sensing mechanisms.
It is a further object of this invention to provide a sensor assembly for measuring the angular position of a shaft. A wheel is coupled with the shaft for incremental angular rotation and through a plurality of revolutions. An incremental sensing mechanism detects the rotation of the wheel and provides an incremental output which is indicative of the incremental angular rotation of the wheel. A change gear is supported by the sensor casing for rotation through predetermined angular segments. A segment sensing mechanism responds to the change gear for providing a segment output indicative of the angular segment in which the wheel is disposed. An actuation mechanism interconnects the wheel and the change gear for rotating the change gear through each of the predetermined angular segments for each occurrence of rotation of the wheel completely through a predetermined number of increments of angular rotation and to prevent rotation of the change gear during rotation of the wheel through each of the predetermined number of increments of rotation.
The subject invention also provides a method of calibrating a position sensor of a type that measures the incremental angular rotation of a shaft and the segment in which the shaft is disposed to produce the final angular position of shaft. The method includes the steps of rotating a shaft, generating a first incremental output having a first incremental amplitude and an incremental phase angle which is indicative of the incremental angular rotation of the shaft, generating a second incremental output having a second incremental amplitude and the incremental phase angle which is indicative of the incremental angular rotation the shaft, generating a first segment output having a first segment amplitude and a segment phase angle which is indicative of the angular segment in which the shaft is disposed, and generating a second segment output having a second segment amplitude and the segment phase angle phase which is indicative of the angular segment in which the shaft is disposed.
The method further includes performing a Fourier analysis on the incremental and segment outputs from the sensor to produce incremental and segment dc components, incremental and segment fundamental outputs and incremental and segment harmonic outputs. A compensation equation is used to provide a common amplitude between the first and the second incremental outputs. A first incremental final output corresponds to the compensated first incremental output and a second incremental final output corresponds to the compensated second incremental output wherein the compensated factors also correct the phase shift errors between the first and the second incremental outputs. Likewise, a compensation equation is used to provide a common amplitude between the first and the second segment outputs. A first segment final output corresponds to the compensated first segment output and a second segment final output corresponds to the compensated second segment output wherein the compensated factors also correct the phase shift errors between the first and the second incremental outputs.
Accordingly, the integrated torque and position sensor sets forth a reduction in the amount of teeth necessary to calculate the angle position which over time ensures greater accuracy in calculating the angle position of a shaft. At the same time, the integrated torque and position sensor utilizes common components for performing both functions of calculating the angle position and the torque of the shaft.
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the
Referring to
The torque sensing mechanism further includes a torque rotor assembly 37 supported by said input shaft 16. The torque rotor assembly 37 includes a back iron 32 which is made of a soft magnetic material, such as a nickel iron alloy. The back iron 32 may be constructed by a stamping process or produced from a powdered metal using a sintering process or through a machining process.
Referring to
Referring to FIGS. 2 and 4–5, the back iron 32 defines a plurality of pockets 38 disposed on the outer surface 36. The torque rotor assembly 37 includes a plurality of magnets 40 disposed in the pockets 38. The magnets 40 may be permanently affixed within the pockets 38 by either crimping, injection molding or by adding an adhesive. The back iron 32 includes a plurality of support structures 42 integrally formed between the pockets 38 on the outer surface 36. The torque rotor assembly 37 includes a retaining ring 44 that is placed over the back iron 32 and is radially spaced from the pockets 38 for applying an inward force against the magnets 40. The retaining ring 44 may not be necessary if the magnets 40 are affixed to the pockets 38 by adhesive or other methods.
Referring to
Referring to
Referring to FIGS. 2 and 7–8, the first torque stator 46 includes a circular base 52 and a plurality of teeth 54 extending inwardly from the circular base 52 in a radial direction. Additionally, the second torque stator 56 includes a circular base 62 and a plurality of teeth 64 extending inwardly from the circular base 62 in a radial direction. As shown in
Referring to
Referring to
The magnetic flux generated by each magnet 40 flows through the stators 46, 56, the support structures 42 of the back iron and through the gap (G). The magnetic circuit that is formed by the magnets 40 has mainly two regions, an upper magnetic zone that is formed between the magnets 40 and the first torque stator 46, and a lower magnetic zone is formed between the magnets 40 and the second torque stator 56. The differential magnetic flux between these two zones flows through the gap (G) and is sensed by the torque magneto-sensitive elements 66. The differential magnetic flux is indicative of the relative rotation between the input shaft 16 and the output shaft 18. At a no load torque condition, both of the zones produce the same amount of flux resulting in a zero differential flux.
As shown in
Referring to FIGS. 1 and 10–14, the integrated sensor 10 includes a circuit board 70 and a sensor casing 78. The sensor casing 78 supports the circuit board 70. The circuit board 70 includes a torque leg 72, a position leg 74 and a flexible portion 76 positioned therebetween. The position leg 74 will be discussed in more detail below. The torque magneto-sensitive elements 66 are disposed on the torque leg 72 and positioned within the gap (G) for sensing a change in the magnetic flux. As shown in
The angle position sensing capability of the integrated sensor 10 measures the angle position of the output shaft 18, or shaft 18. The integrated sensor 10 includes an incremental sensing mechanism 68 that detects the angular position of the shaft 18 and is indicative of the incremental angular rotation or the angular position of the shaft 18 between any angle of 0 and 360 degrees.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to FIGS. 21 and 23–24, the actuation mechanism 129 interconnects the wheel 24 and the change gear 100 when the wheel 24 rotates completely through a predetermined number of increments. Meaning, that for every one hundred and eighty degrees of rotation of the wheel 24, either the first pair of drive teeth 112 engages with either one change tooth 103 in the first plurality of change teeth 102 or one change tooth 105 in the second plurality of change teeth 104, or the second pair of drive teeth 118 engages with either one change tooth 103 in the first plurality of change teeth 102 or one change tooth 105 in the second plurality of change teeth 104 for rotating the change gear 100 through a predetermined angle of thirty six degrees. One skilled in the art will recognize that a change gear 100 may be provided with any number of change teeth. For example, ten change teeth may be used for the first plurality of change teeth 102 and the second plurality of change teeth 104 resulting in a total of twenty teeth and rotating the change gear 100 eighteen degrees upon each occurrence of the drive teeth 112 engaging one of the change teeth in either the first plurality of change teeth 102 or the second plurality of change teeth 104.
As shown in
Referring to
Referring to
Referring to
Whenever the shaft 18 is rotated to any angle which is not equal to a multiple of one hundred and eighty degrees the either the first blocking cam 126 engages with the engagement surface 110 disposed on the first plurality of change teeth 102 or the second blocking cam 128 engages with the engagement surface 110 disposed on the second plurality of change teeth 104.
Referring to
Referring to
P1=A1 sin θ1 (a)
P2=B2 cos(θ1+δ1,2) (b)
The variables A1 and B2 are defined as a first incremental amplitude and a second incremental amplitude, respectively. The angle θ1 is the incremental phase angle of the shaft and δ1,2 is defined as an incremental quadrature error angle. Ideally, P1 and P2 are shifted ninety degrees from each other and the incremental quadrature error angle is equal to zero.
As stated above, the segment magneto-sensitive elements 108 are disposed on the torque leg 72 of the circuit board 70. A first segment magneto-sensitive element 138 and a second segment magneto-sensitive element 140 output a segment output which correlates to an angle of between 0 and 360 degrees. The segment output will be used to provide the segment or revolution in which the shaft 18 or the wheel 24 is disposed. The segment output includes a first segment output, P3, which is an output produced from the first segment magneto-sensitive element 138 and a second segment output, P4, which is an output produced from the second segment magneto-sensitive element 140.
Referring to
P3=A3 sin θ2 (c)
P4=B4 cos(θ2+δ3,4) (d)
The variables A3 and B4 are defined as a first segment amplitude and a second segment amplitude, respectively. The angle θ2 is the segment phase angle is the angle position of the shaft and δ3,4 is defined as a segment quadrature error angle. Preferably, P3 and P4 are shifted ninety degrees from each other and the segment quadrature error angle is equal to zero.
As shown in
To show the derivation of the solver equation, the amplitudes A1, A3 will be defined by Am and the amplitudes B2, B4 will be defined by Bm. The angles θ1 and θ2 are defined by the angle θm. Finally, the quadrature error angles δ1,2 and δ3,4 are defined as δ.
The equations (a), (b), (c), and (d) may be rewritten as:
P1(or P3)=Am sin θm (f)
P2(or P4)=Bm cos(θm+δ) (g)
It is important to note that P1 and P3 are not equal to each other. Likewise, P2 and P4 are not equal to each other. The purpose of writing equations (f) and (g) is to show that the same derivation for establishing the application of the solver equation using the outputs P1 and P2 also applies to the outputs P3 and P4.
Due to tolerances created in the manufacture of various components used in the integrated sensor, it is necessary to generate an equation where Am=Bm. Additionally, it is necessary to ensure that a phase shift of ninety degrees exists between the sinusoidal and cosinusodial outputs.
A gain factor of
is multiplied to equation (g) for generating the following equation:
Equation (h) may be re-written using equations (f) and (g):
In solving for Am cos θm in equation (i), equation (j) is produced resulting in an equation that represents the different amplitude Bm and the error angle δ in the form of a common amplitude Am.
By arbitrarily setting P′2(or P′4) to Am cos θm, it is possible to define the numerator of the solver equation as follows:
f(θm, φ)=P1(or P3)cos φ−P′2(or P′4)sin φ=Am sin(θm−φ)=0 (k)
The denominator for the solver equation is defined as the following:
The solver equation is shown as the following after substituting equations (l) and (m) into equation (e):
Accordingly, φold is an initial angle value which is arbitrarily set to any angle between 0 and 360 degrees, after φold is inserted into the solver equation (n), an angle φnew is produced, if the angle φnew is not a pre-determined angle, angle φnew is set to φold, and equation (n) is solved again generating a new angle φnew. Depending on which of the outputs P1, P2, P3, P4 were inserted into the solver equation (n), the converged angle φnew is assigned to either a final incremental angle position or a final segment angle. If the outputs P1, P2 were inserted into the solver equation (n), the converged angle φnew is set to the final incremental angle and the output is any angle between 0 and 360 degrees. If P3, P4 was inserted in the solver equation (n), then the converged angle φnew is set to the actual segment angle.
A total of five actual segment angles correspond to the five change teeth of the first plurality of change teeth 102. Likewise, five actual segment angles correspond to the five change teeth of the second plurality of change teeth 104. As either the first pair of drive teeth 112 or the second pair of drive teeth 118 engages with any change tooth 103 of the first plurality of change teeth 102 or any change tooth 105 of the second plurality of change teeth 104, the change gear 100 and the segment magnet 106 is rotated a total of thirty six degrees in either direction. In response to the segment magnet 106 being rotated by thirty six degrees, new values for P3 and P4 are outputted from the segment magneto-sensitive elements 138, 140 and inserted into the solver equation (n) for producing the actual segment angle. As the user rotates the shaft 18 over the full range of shaft travel of +/−900 degrees, the wheel 24 engages the change teeth 102,104 every one hundred and eighty degrees or ten times (total angular rotation of shaft/# of change teeth) resulting in a total of ten final segment angles. The selection of the number of change teeth is calculated by taking the total angular travel of the shaft 18 divided by the angle between the first pair of drive teeth 112 and the second pair of drive teeth 118. Accordingly, the selection of ten teeth dictates the number of steps represented in the sinusoidal and cosinusodial outputs of P3 and P4 respectively. Every two turns of the segment magnet 106 is indicative of a new revolution in which the shaft 18 is disposed. As stated earlier, one skilled in the art will recognize that a change gear 100 with five change teeth would result in the drive teeth engaging the change teeth every three hundred and sixty degrees. As a result, a total of five final segment angles would be utilized.
Upon rotating the shaft 18, the ring magnet 82 rotates in the same direction generating a new set of output values P1 and P2. The incremental outputs P1 and P2 are then applied to the solver equation (n) for producing the final incremental angle.
An algorithm uses the actual segment angle to produce the final segment angle (FinalSegAng) and a final angle position equation determines a final angle position (FinalPos). The algorithm and the final angle position equation are defined by equations (o) and (p) respectively:
Actual Segment Angle−Δθ≦FinalSegAng≦Actual Segment Angle+Δθ (o)
FinalPos=FinalIncAng+n·360 degrees (p)
It should be noted that anyone skilled in the art may derive different final segment angles (FinalSeqAng) other than those defined in Table 1 and may also assign different integers to the FinalSegAng. The actual segment angle which is produced from the solver equation (n) will ultimately converge on any of the final segment angles with the tolerance Δθ. After the final segment angle has been determined by matching the actual segment angle, the integer n is determined, and n and the FinalIncAngle produced by the solver equation (n) using outputs P1, and P2 are inserted into the final angle position equation (p) to produce the final position angle (FinalPos). Ideally, each final segment angle is configured to represent each change tooth on the change gear 106. As the number of change teeth utilized on the change gear either increase or decrease, the number of final segment angles used will decrease or increase. Accordingly, the final position angle (FinalPos) is an angle between +/−900 degrees and is indicative of the angle in which the shaft 18 is disposed. These values depend on the initial position of the shaft 18 and the change gear 100. The calculation of the final position angle of between +/−900 may extend to a larger angle and may also be smaller than +/−900. The limit of the final angle position will depend on the number of change teeth utilized on the change gear 106.
Each of the calculated final segment angles generated by the solver equation (n) has a tolerance of +/−18 degrees, which is equivalent to the angle rotation of the change gear at thirty six degrees. The calculation of the final incremental angle, the actual segment angle, the final segment angle and the final angle position will be performed on a device not included with the integrated sensor 10. The device may include a controller electrically coupled to the integrated sensor 10 which receives the outputs P1, P2, P3, P4. Referring to
Referring to
Method of Calibrating and Compensating the Outputs of the Integrated Sensor
Due to tolerance issues or design variations of the various components utilized in the integrated sensor 10, different amplitudes may exist between A1 and B2 for the incremental outputs P1 and P2; and A3 and B4 for the segment outputs P3 and P4. Further, a ninety degrees phase shift between the angles may not exist between the incremental outputs P1 and P2 and the segment outputs P3 and P4. Other errors may lead to unbalanced amplitudes, positive and negative cycles may not be spanned over 180 degrees, and higher order harmonics may be present in the outputs P1, P2, P3 and P4. The sources of these errors or non-idealities may include, magnet anisotropies, cocking of either the ring magnet 82 or segment magnet 106 after assembly, variations between the incremental and the segment magneto-sensitive element's sensitivity (mV/G), and a voltage offset (VOQ) variation. The voltage offset (VOQ) is a produced by the magneto-sensitive elements.
Referring to
Referring to
Referring to
In step 210, the calibration method samples and collects the incremental outputs P1 and P2 from zero to three hundred and sixty degrees. In step 212, the voltage offset (VOQ) is subtracted from the collected incremental outputs P1 and P2 as produced by the incremental magneto-sensitive elements 134, 136. In step 214, a Fourier analysis is performed on P1 to produce a first incremental dc component DC_P1, a plurality of first incremental harmonic outputs, and a first incremental fundamental output. It should be noted that the first incremental dc component DC_P1 corresponds to a harmonic order of zero after performing the Fourier analysis. The plurality of first incremental harmonic outputs include a plurality first incremental harmonic amplitudes AN_P1 and a plurality of first incremental harmonic phase angles PhN_P1, where N is the order or the number of harmonics generated by the Fourier analysis. In the illustrated embodiment, the desired waveform is the first incremental fundamental output which corresponds to the first order harmonic (N=1) after performing the Fourier analysis. The remaining plurality of first incremental harmonic outputs corresponds to errors generally present in P1 and are defined as first incremental errors. It should be noted that additional or different harmonic outputs may be selected as the desired waveform or the waveform that represents errors in P1 and the selection of the harmonic outputs which comprise errors or are selected as the desired waveform are not limited by the illustrated embodiment. The first incremental fundamental output includes a first incremental fundamental amplitude A1_P1 and a first incremental fundamental phase angle Ph1_P1. Accordingly, DC_P1, AN_P1, PhN_P1, A1_P1, and Ph1_P1 are defined as the first incremental calibration parameters.
In step 216, the Fourier analysis is also performed on P2 to produce a second incremental dc component DC_P2, a plurality of second incremental harmonic outputs, and a second incremental fundamental output. The second incremental dc component DC_P2 corresponds to a harmonic order of zero after performing the Fourier analysis. The plurality of second incremental harmonic outputs include a plurality of second incremental harmonic amplitudes AN_P2 and a plurality of second incremental harmonic phase angle PhN_P2, where N is an integer and is the order or the number of harmonics generated by the Fourier analysis. The desired waveform is the second incremental fundamental output which corresponds to the first order harmonic after performing the Fourier analysis. The remaining plurality of second incremental harmonic outputs corresponds to the errors generally present in P2 and are defined as first incremental errors. It should be noted that additional or different harmonic outputs may be selected as the desired waveform or the waveform that represents errors in P2 and the selection of those harmonic outputs are not limited by the illustrated embodiment. The second incremental fundamental output includes a second incremental fundamental amplitude A1_P2 and a second incremental fundamental phase angle Ph1_P2. Accordingly, DC_P2, AN_P2, PhN_P2, A1_P2, and Ph1_P2 are defined as the second incremental calibration parameters.
Referring to
A first incremental adder 252 and a second incremental adder 254 is used to eliminate the voltage offset (VOQ) as generated from the incremental magneto-sensitive elements 134,136. A third incremental adder 256 subtracts DC_P1 from the P1 to create a first incremental adjusted output P′1. Likewise, a fourth incremental adder 258 subtracts DC_P2 from P2 to create a second incremental adjusted output P′2.
After producing P′1, a previous position of the shaft (prevpos), AN_P1, and PhN_P1 are inserted into a first incremental compensation block 260 wherein a first incremental compensation equation eliminates the first incremental harmonic outputs. This in effect eliminates most of the non-idealities in the P1 output and produces the first incremental final output P′1. The first incremental compensation equation is defined as:
P″1=P′1−AN—P1*sin [(prevpos+PhN—P1*N)] (q)
It should be noted that if the previous position (prevpos) of the shaft was not known, an initialization routine will produce the (prevpos) value of the shaft. The first incremental final output P″1 is the compensated value for P1.
After producing P′2 from the fourth incremental adder 258, the previous position of the shaft (prevpos), AN_P2, and PhN_P2 are inserted into a second incremental compensation block 262 wherein a second incremental compensation equation eliminates the second incremental harmonic outputs. This in effect eliminates most of the non-idealities in the P2 output and produces a second incremental corrected output P″2. The second incremental compensation equation is defined as:
P″2=P′2−AN—P2*sin [(prevpos+PhN—P2*N)] (r)
The output of the incremental compensation equation converges on a single value to produce the second incremental corrected output P″2.
After generating P″2, P″2 is multiplied to a first gain block 264 wherein the gain block includes an incremental gain factor which is defined by the ratio of fundamental amplitudes:
A1—P1/A1—P2 (s)
By multiplying P″2 with the incremental gain factor, this produces a second incremental normalized output P″2. This step is performed such that the amplitudes of P1 and P2 are equal.
By establishing a common amplitude between P1 and P2, the next step is to calculate the incremental quadrature error angle δ1,2 between the outputs P1 and P2, ideally a ninety degrees phase shift is required between the outputs P1 and P2. To calculate δ1,2, a fifth incremental adder 268 adds ninety degrees to Ph1_P1, and Ph1_P2 is subtracted from the sum of ninety degrees and Ph1_P1 to calculate the incremental quadrature error angle δ1,2. After solving for δ1,2, an incremental correction block 266 produces a second incremental final output {tilde over (P)}2. The incremental correction block 266 includes an incremental correction equation and is defined by the following equation:
{tilde over (P)}2=[(P′″2+P″1 sin δ1,2)/cos δ1,2] (t)
Accordingly, the final incremental output {tilde over (P)}2 is the compensated value for P2.
By employing the method as described above, the objective of providing a common amplitude between the incremental outputs P1 and P2 and achieving a phase shift of substantially ninety degrees between the angles of the incremental outputs P1 and P2 is satisfied. As shown in
It is now possible to employ the solver equation to produce the final incremental angle of the shaft 18. As stated above, the final incremental angle is any angle between 0 and 360 degrees. Referring to
The variable φnew will converge on a value of between 0 and 360 degrees and is defined as the final incremental angle. As stated above, the converged angle φnew is assigned to the final incremental angle.
Referring to
In step 310, the voltage offset (VOQ) is subtracted from the segment outputs P3 and P4 as produced by the segment magneto-sensitive elements 138, 140. In step 312, a Fourier analysis is performed on P3 to produce a first segment dc component DC_P3 and a first segment fundamental output. It should be noted that the first segment dc component DC_P3 corresponds to a harmonic order of zero after performing the Fourier analysis. The first segment fundamental output includes a first segment fundamental amplitude A1_P3 and a first segment fundamental phase angle Ph1_P3. Accordingly, DC_P3, A1_P3, and Ph1_P3 are defined as the first segment calibration parameters.
In step 314, the Fourier analysis is also performed on P4 to produce a second segment dc component DC_P4 and a second segment fundamental output. The second segment dc component DC_P4 corresponds to harmonic order of zero after performing the Fourier analysis. The second segment fundamental output includes a second segment fundamental amplitude A1_P4 and a second segment fundamental phase angle Ph1_P4. Accordingly, DC_P4, A1_P4, and Ph1_P4 are defined as the second segment calibration parameters.
Referring to
A first segment adder 352 and a second segment adder 354 are used to eliminate the voltage offset (VOQ) generated from the segment magneto-sensitive elements 138,140 and the adders 352, 354. A third segment adder 356 subtracts DC_P3 from the P3 output to create a first segment final output P′3. Accordingly, P′3 is the compensated value for P3. Likewise, a fourth segment adder 358 subtracts DC_P4 from the P4 output to create a second segment adjusted output P′4.
After generating P′4, P′4 is multiplied to a segment gain block 360 wherein the gain block includes a segment gain factor which is defined by the ratio of fundamental amplitudes:
A1—P3/A1—P4 (v)
By multiplying P′4 with the segment gain factor, this produces a second incremental normalized output P″4. This step is performed such that the amplitudes of P3 and P4 are equal.
By establishing a common amplitude between P3 and P4, the next step is to calculate the segment quadrature error angle δ3,4 between the outputs P3 and P4, ideally a ninety degrees phase shift is required. To calculate δ3,4, a fifth incremental adder 362 adds ninety degrees to Ph1_P3, and Ph1_P4 is subtracted from the sum of ninety degrees and Ph1_P3, to calculateδ3,4. After solving forδ3,4, a segment correction block 364 produces a second segment final output {tilde over (P)}4. The segment correction block 364 includes a segment correction equation and is defined by the following equation:
{tilde over (P)}4=[(P″4+P′3 sin δ3,4)/cos δ3,4] (w)
Accordingly, the second segment final output {tilde over (P)}4 is the compensated value for P4.
By employing the method as described above, the objective of providing a common amplitude between the segment outputs P3 and P4 and achieving a phase shift of substantially ninety degrees between the angles of the segment outputs P3 and P4 is satisfied. As shown in
It is now possible to employ the solver equation to produce the final segment angle of the shaft 18. The first and the second segment final outputs are inserted into a solver equation block 366 where the solver equation provides the final segment angle of the shaft 18. The solver equation (n) from above is re-written as:
The variable φnew will converge to the actual segment angle which is a value between 0 and 360 degrees.
After calculating the final incremental angle and the actual segment angle, the actual segment angle is compared to the final segment angle and corresponding integer (n) as listed in Table 1 above. In response to comparing the actual segment angle to the final segment angle, the final position equation associated with the final segment angle takes the final incremental angle as calculated from equation (u) and inserts the final incremental angle and the corresponding integer (n) into the final angle position equation (p) to produce the final angle position of the shaft 18 which may be any angle between +/−900 degrees.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.
This application claims the benefit of the U.S. Provisional Patent Application Ser. No. 60/542,511, filed on Feb. 6, 2004, which is hereby incorporated by reference.
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