CA1165888A - Method and apparatus for compensating a sensor - Google Patents
Method and apparatus for compensating a sensorInfo
- Publication number
- CA1165888A CA1165888A CA000320500A CA320500A CA1165888A CA 1165888 A CA1165888 A CA 1165888A CA 000320500 A CA000320500 A CA 000320500A CA 320500 A CA320500 A CA 320500A CA 1165888 A CA1165888 A CA 1165888A
- Authority
- CA
- Canada
- Prior art keywords
- sensor
- digital
- signal
- output
- processing means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
- G01D18/002—Automatic recalibration
- G01D18/004—Continuous recalibration
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/30—Nc systems
- G05B2219/37—Measurements
- G05B2219/37009—Calibration of vision system, camera, adapt light level
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/30—Nc systems
- G05B2219/37—Measurements
- G05B2219/37151—Handling encoder signal, compensation for light variation, stray light
Abstract
ABSTRACT OF THE DISCLOSURE
A sensor is compensated through the use of a closed loop comprising a digital processor, a digital-to-analog converter and a comparator having inputs coupled to the converter and the sensor and an output fed back to the digital processor.
During calibration of the sensor, a signal from the sensor is tracked by the digital processor and at least one of the values characteristic of the sensor signal is stored in the digital processor. The stored value is used as a or in the computation of a reference by the digital processor which is compared with the sensor signal during operation of the sensor to approximately compensate the sensor for gain, offset, drift or degradation in the quality of the sensor signal.
A sensor is compensated through the use of a closed loop comprising a digital processor, a digital-to-analog converter and a comparator having inputs coupled to the converter and the sensor and an output fed back to the digital processor.
During calibration of the sensor, a signal from the sensor is tracked by the digital processor and at least one of the values characteristic of the sensor signal is stored in the digital processor. The stored value is used as a or in the computation of a reference by the digital processor which is compared with the sensor signal during operation of the sensor to approximately compensate the sensor for gain, offset, drift or degradation in the quality of the sensor signal.
Description
I :1 6~8~3 .
-- 1 ~
1 This invention relates to the use of a digital pro-
-- 1 ~
1 This invention relates to the use of a digital pro-
2 cessor or computer for compensation of sensors.
3 A wide variety of sensors are utilized for differen~
4 purposes including the control of processes and equipment When utilizing sensors for control purposes, it is particularly 6 impor~ant, in many instances, to avoid gain, o~fset, drift 7 and degradation problems which can produce unreliability.
8 In the area of optical sensors, an LED (light emit-9 ting diode)/phototransi tor combination is widely used in a variety of applications. One dist~nc~ advan~age o~ this com-11 bination is the relatively low cost. However, the gain and 12 offset of the combination differ from one LED/photo~ransistor 13 to another LED/phototransistor, and the LED and phototransistor 14 are subject to short term drift with temperature as well as long term degrada~ion~ Although such a combination may be 16 utilized in certain digital applications, the combination is 17 generally unsuitable for analog applications. Som~of the 18 aforegoing difficulties may be aliminated by AC coupling the 19 LED to the phototransistor. However, variations in gain still present a problemO Moreover, the AC coupled combination 21 results in a relatively high C05t- Another optical combina-22 tion which is sometimes utilized comprises a sensor, a refer-23 ence, a comparator and a uni~orm light source. A photocell 24 may be utilized in con~unction with the uniform ligh~ source as the reference and ~he sensor itself may comprise a pho~o-26 transistor. Although gain, offset, short and long term drift 27 are minimized, such a combination is quite costly and there~
28 fore unsuitable ~or many applications.
29 It is ~n object of this invention to provide a ' " " ' :
I 1~5~3~3~3 method and apparatus which will permit the u~e of a sensor in a variety of applications even though the sensor is characterized by short or long term drift.
It is a further object of this invention to pro-vide a method and apparatus which will permit the use ofsensors which may vary in gain and/or offset.
It is a further object of this invention to pro-vide a method and apparatus so as to permit the use of relatively low cost sensors.
In accordance with a particular embodiment of the invention there is provided the method of usiny a sensor producing an analog signal with a digital process-ing means. The method includes calibration steps conver-ting a digital output signal from the processing means to a corresponding analog signal and comparing a sensed analog signal produced by the sensor with the correspond-ing analog signal. The digital output signal of the processing means is changed in the absence of a first predetermined relationship between the sensor analog signal and the corresponding analog signal. The fore-going steps are reiterated until the first predetermined relationship exists between the sensor signal and the corresponding analog signal. The foregoing steps are repeated for different instantaneous sensor analog signals to ~enerate reference signals, corresponding to at least one of the maximum amplitude, minimum amplitude and a combination of the maximum and minimum amplitudes of the sensor analog signal. Information representing at least one of the digital output signals correspondiAg to the maximum amplitude, the minimum amplitude and a combination of the maximum and minimum amplitudes of the sensor analog signal are stored in the processing ~s~
~.~
. , .
1 3 ~5~3~3 - za -means, The method further includes the measuring steps of generating a calibrated digital output signal at the output of the processing means from the at least one stored digital signal and converting the calibrated digital output signal to a calibrated analog signal value.
m e calibrated analog signal is compared to an analog signal produced by the sensor and a calibrated analog control signal is produced in response to the comparison.
From a different aspect, and in accordance with the invention there is provided an apparatus for compensating a sensor~ The apparatus includes digital processing means and digital-to-analog converter means having an input coupled to an output of the digital processing means. Comparator means are provided with a first input coupled to the output of a converter mean~, a second input adapted to be coupled to the sensor and an output coupled to the processing means to fonm a closed loop~ The digital processing means includes means for iteratively computing digital output signals and coupling the iteratively computed digital signals to the converter means. Also provided are means for continuing iterations until at least one of the iteratively computed digital signals as converted has a predetermined relation-ship with an instantaneous sensor output signal as deter-mined by the output of the comparator~ The digital processing means further includes means for iteratively producing other digital signals each having the predeter-mined relationship with other instantaneous signals at the sensor output, and means for storing information~
representing at least one of the digital signals corres-ponding to a maximum sensor output, a minimum sensor out-put and a combination of the maximum and minimum sensor , , ' ~:, .3 8 ~
- 2b -outputs so as to represent a selective characteristic of the sensor. Further provided are means for generating a sensor calibrated digital output signal from the at least one of the digital signals corresponding to a selected charackeristic of the sensor. The converter means converts the sensor calibrated digital output signal to a calibrated analog signal and the comparator compares the calibrated analog signal to the sensor out-put. Means are also provided for providing a control signal in response to the comparison.
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,, ~
1 In a particularly preferred embodiment of the inven-2 tion, the analog sensor signal is substantially sinu~oidal and 3 the digital values which are stored in the digital processor 4 during calibration represent the maximum and ~ini~um. The digltal value for purposes of establishing a reference are 6 then computed in accordance with the formula ( _ m) 7 sin D + (maximum minimum) where D equals the angle of the 8 sinusoidal signal corresponding to the stored digital value.
9 ~
Fig. 1 is a block diagram of apparatus utilized in ll a preferred embodiment of the invention;
12 Fig. 2 is a block diagram of an analog equivalent 13 for the computation performed by the processor of Fig. l;
14 Fig. 3A is a waveform representing the analog sensor lS signal applied to the comparator of Fig. l;
16 Fig. 3B is a waveform represen~ing the output o ~he 17 comparator of Fig. l;
18 Figo 4 is a flow diagram of the calibration phase 19 performed by the processor of Fig. l; and Fi8. 5 is a flow diagram o the computation and use 21 of reference values generated by the processor of Fig. 1.
22 As shown in Fig. 1, a clos~d loop including a digi-23 tal processor 10 is utiLized to provide compensation of an 24 analog sensor. The loop includes a digital-to-analog convert-er 12 and a camparator 14 having a first input A coupled to 26 the analog sensor and a second input B coupled to the output 27 of the digital-to-analog converter 12. The output of the com-28 parator is applied as a digital or binary signal (1 or 0) to 29 the processor 10.
3 ~ ~3 1 During the calibration phase of opera~lon, ~he 2 analog sensor signal appLied to the input A o~ the comparator 3 14 is tracked by digi~al values produced by the processor 10 4 and applied to thP converter 12. For each instan~aneous S value of the analog sensor signal a~ the input A, the pro-6 cessor 10 iteratively produces a plurality of digltal values 7 until the outpu~ of the comparator 14 indicates that the 8 digital value as converted and applied to the input B is 9 equal to or corresponds with the analog sensor signal as applied to the input A. The same process is repeated for 11 subsequent instantaneous analog sensor signal values charac-12 teristic of ~he analog sensor signal which are stored in the 13 processor 10 during the calibration phase so as to permit the 14 subsequent use of that characteristic value as a sensor ref-erence to be con~erted by the converter 12 and applied to the 16 input B during the operation mode thereby providing for an 17 appropria~ely compensated analog sensor~ It will of course 18 be appreciated that the step of calibration may be repeated 19 many times and frequently so as to assure ~hat the analog sen-sor is always appropriately compensated regardless of shor~
21 term or long term drift.
22 In a particularly preferred embodiment of the in-23 vention, the analog sensor signal may be sinusoidal as shown 24 in Fig. 3A. In that case, it is desirable to store during calibration the maximum and minimum values which may then be 26 utilized to compute any of a number of reference digital values 27 for comparison with the analog sensor signal in the opera~ing 28 mode.
29 The nature of the computations which are performed 1 by the processor 10 are depic~ed in analog equivalent form 2 in the diagram of Fig. 2. A~ter the maximum and minimum 3 values of the analog sensor signals have been detected by a 4 maximum peak detec~or 16 and a minimum peak detector 18 as shown in Fig. 2, the outputs from the detectors 16 and 18 are 6 utilized by su~mers 20, 22 and 24 and constant networks 26, 7 28 and 30 so as to produce analog values at the A input to 8 the comparator 14 which correspond to 0, 30~ 45~ or 90 on 9 the sinusoidal signal depending upon the position of the angle select switch 32. The values at the switch 32 are 11 applied to the comparator 14 for comparison with the analog 12 signal during the operating mode. The ou~put from the com-13 parator corresponds with the position of the switch angle 14 (X) or (180-X~ at the output of an inverter 34.
From the foregoing, it will be unders~ood that the 16 various computation functions which are performed on an iter-17 ative basis by the processor 10 may therefore be performed by 18 an analog computer cireuit as shown in Figo 2. However, con-19 siderably more flexibility is aforded by the processor 10 Moreover, the advent of the microprocessor permits ~he compen~
21 sation of the sensor as disclosed in Figo 1 to be provided at 22 relatively low cost consistent with one important objective 23 of this invention.
24 Where the angle select switch 32 in the position shown in Fig. 2, the analog sensor signal is compared with 26 the value of the sinusoidal signal of Fig. 3A a~ 0 or (180-27 0). Utilizing the 0 point and the 180 point as the refer-28 ence produces a square wave logic signal at the output o the 29 comparator during the operate mode as shown in Fig. 3B where ~ 1fi5~
~ 6 --transitions occur at the 0 and 180 points on the analoy sensor signal.
As mentioned previously, the analog sensor signal is tracked durin~ the calibration mode as will S now be described with reference to the flow diagram of Fig. 4. In the flow diagram of ~ig, 4, it is assumed that an analog sensor of the type disclosed in Canadian application 310,368 filed August 30, 1978, assigned to the assignee of this invention, is utilized in connection with the control of a stepper motor as disclosed therein.
The sinusoidal signal produced by that sensor as shown in the waveform of Fig. 3A is produced as a result of stepping the motorO
Upon initiating calibration(40), th0 step motor of the system is moved one step forward (42) which sets a timer (44)O A loop is then entered in which the instantaneous sensor value is read (46), The reading of the sensor value is accomplished by iteratively producing digital values until the comparator output as shown in Fig. 1 produces a logic l. If the instantaneous analog sensor value is greater than the heretofore stored current maximum value (48), a new maximum value (50) is set to the current instantaneous value. On the other hand, if the instantaneous value is less than the current minimum value stored (52), a new minimum value is set in accordance with the current reading (54), If after the set ting of the maximum or minimum values(50) and (54), the timer has not yet timed out (56~, the loop is repeatedO If the timer has timed out, the maximum and minimum values which ~ ~fi~f.3gt~
1 have been set and stored are ~hen utilized to set and s~ore 2 the amplitude of the analog sensor value at the maximum 3 minus the minimum value divided by 2 (58) and the proces~or 4 exits from the calibration mode (60).
Referring now to Fig. 5, the processor may enter 6 the operate mode (62) in which the appropriate reference 7 signal is generated in accordance with the equation:
8 Re~. = (maximu= minimum)sin D + (maximum minimum) 9 where D is the reference point on the sinusoidal waveform of Fig. 3A corresponding to the angle of the switch 32 o Fig. 2.
11 The output of the comparator 14 changes state whenever ~he 12 sensor reference signal and ~he sensor signal are equal (66).
13 As noted previously, the processor during the cali-14 bration mode will produce iterative digital values until cor-re~pondence or equality is achieved between the sensor signal 16 and the digital value as co~verted by the converter 12 as 17 shown in Fig. 1. The processor may be programmed in dif~erent 18 ways to iteratively produce the digital values. For example, 19 the digital value produced at the output of the processor may be continuously incremented until equality or correspondence 21 is achieved. In the alterna~ive, the technique of SuccssSive 22 approximations may be utilized to shorten the search for the 23 corresponding digital value. Of course, the processor 10 may 24 be programmed in other ways to allow the digital values rom the processor to track the analog sensor slgnal.
26 The Fairchild F-8 microprocessor is particularly 27 well-suited for use in practicing the in~en~ion. However, the 28 processor may be o various types and siæes.
29 In the aforesaid copending application Serial No.
.
I 1 ~i5~3~3 ~3 1 310,368 the particular sensor comprises a light emik~ing 2 diode in combination with a phototransistor. As mentioned 3 previously, such a combination is relatively low cost and the 4 use of the appara~us and method disclosed herein psrmit the low cost combination ~o be utilized without any trade-off 6 with respect to drift and degradation or variations in gain 7 and offset. It will of course be appreciated that other sen-8 sors may be utilized and ~he invention is not limited ~o the 9 use of any particular type of sensor. Moreover, the inven-tion is not limited to the use o~ the method and apparatus 11 disclosed herein with respect to.any particular application 12 although the invention has been found to be extremely useful 13 in a control of stepper motors as disclosed in the aforesaid 14 copending application.
Although a particular embodiment of the invention 16 has been shown and described and various modifications have 17 been suggested~ it will be understood that the invention may 18 be incorporated in various embodiments and modifications with-19 out departing from the true spirit and scope of the invention as se~ forth in the appended claims.
8 In the area of optical sensors, an LED (light emit-9 ting diode)/phototransi tor combination is widely used in a variety of applications. One dist~nc~ advan~age o~ this com-11 bination is the relatively low cost. However, the gain and 12 offset of the combination differ from one LED/photo~ransistor 13 to another LED/phototransistor, and the LED and phototransistor 14 are subject to short term drift with temperature as well as long term degrada~ion~ Although such a combination may be 16 utilized in certain digital applications, the combination is 17 generally unsuitable for analog applications. Som~of the 18 aforegoing difficulties may be aliminated by AC coupling the 19 LED to the phototransistor. However, variations in gain still present a problemO Moreover, the AC coupled combination 21 results in a relatively high C05t- Another optical combina-22 tion which is sometimes utilized comprises a sensor, a refer-23 ence, a comparator and a uni~orm light source. A photocell 24 may be utilized in con~unction with the uniform ligh~ source as the reference and ~he sensor itself may comprise a pho~o-26 transistor. Although gain, offset, short and long term drift 27 are minimized, such a combination is quite costly and there~
28 fore unsuitable ~or many applications.
29 It is ~n object of this invention to provide a ' " " ' :
I 1~5~3~3~3 method and apparatus which will permit the u~e of a sensor in a variety of applications even though the sensor is characterized by short or long term drift.
It is a further object of this invention to pro-vide a method and apparatus which will permit the use ofsensors which may vary in gain and/or offset.
It is a further object of this invention to pro-vide a method and apparatus so as to permit the use of relatively low cost sensors.
In accordance with a particular embodiment of the invention there is provided the method of usiny a sensor producing an analog signal with a digital process-ing means. The method includes calibration steps conver-ting a digital output signal from the processing means to a corresponding analog signal and comparing a sensed analog signal produced by the sensor with the correspond-ing analog signal. The digital output signal of the processing means is changed in the absence of a first predetermined relationship between the sensor analog signal and the corresponding analog signal. The fore-going steps are reiterated until the first predetermined relationship exists between the sensor signal and the corresponding analog signal. The foregoing steps are repeated for different instantaneous sensor analog signals to ~enerate reference signals, corresponding to at least one of the maximum amplitude, minimum amplitude and a combination of the maximum and minimum amplitudes of the sensor analog signal. Information representing at least one of the digital output signals correspondiAg to the maximum amplitude, the minimum amplitude and a combination of the maximum and minimum amplitudes of the sensor analog signal are stored in the processing ~s~
~.~
. , .
1 3 ~5~3~3 - za -means, The method further includes the measuring steps of generating a calibrated digital output signal at the output of the processing means from the at least one stored digital signal and converting the calibrated digital output signal to a calibrated analog signal value.
m e calibrated analog signal is compared to an analog signal produced by the sensor and a calibrated analog control signal is produced in response to the comparison.
From a different aspect, and in accordance with the invention there is provided an apparatus for compensating a sensor~ The apparatus includes digital processing means and digital-to-analog converter means having an input coupled to an output of the digital processing means. Comparator means are provided with a first input coupled to the output of a converter mean~, a second input adapted to be coupled to the sensor and an output coupled to the processing means to fonm a closed loop~ The digital processing means includes means for iteratively computing digital output signals and coupling the iteratively computed digital signals to the converter means. Also provided are means for continuing iterations until at least one of the iteratively computed digital signals as converted has a predetermined relation-ship with an instantaneous sensor output signal as deter-mined by the output of the comparator~ The digital processing means further includes means for iteratively producing other digital signals each having the predeter-mined relationship with other instantaneous signals at the sensor output, and means for storing information~
representing at least one of the digital signals corres-ponding to a maximum sensor output, a minimum sensor out-put and a combination of the maximum and minimum sensor , , ' ~:, .3 8 ~
- 2b -outputs so as to represent a selective characteristic of the sensor. Further provided are means for generating a sensor calibrated digital output signal from the at least one of the digital signals corresponding to a selected charackeristic of the sensor. The converter means converts the sensor calibrated digital output signal to a calibrated analog signal and the comparator compares the calibrated analog signal to the sensor out-put. Means are also provided for providing a control signal in response to the comparison.
.... .. ... .. . . .. .. ~ . . . . . . . . . .. .. . . .
-- - 1 1 6!~8~
,, ~
1 In a particularly preferred embodiment of the inven-2 tion, the analog sensor signal is substantially sinu~oidal and 3 the digital values which are stored in the digital processor 4 during calibration represent the maximum and ~ini~um. The digltal value for purposes of establishing a reference are 6 then computed in accordance with the formula ( _ m) 7 sin D + (maximum minimum) where D equals the angle of the 8 sinusoidal signal corresponding to the stored digital value.
9 ~
Fig. 1 is a block diagram of apparatus utilized in ll a preferred embodiment of the invention;
12 Fig. 2 is a block diagram of an analog equivalent 13 for the computation performed by the processor of Fig. l;
14 Fig. 3A is a waveform representing the analog sensor lS signal applied to the comparator of Fig. l;
16 Fig. 3B is a waveform represen~ing the output o ~he 17 comparator of Fig. l;
18 Figo 4 is a flow diagram of the calibration phase 19 performed by the processor of Fig. l; and Fi8. 5 is a flow diagram o the computation and use 21 of reference values generated by the processor of Fig. 1.
22 As shown in Fig. 1, a clos~d loop including a digi-23 tal processor 10 is utiLized to provide compensation of an 24 analog sensor. The loop includes a digital-to-analog convert-er 12 and a camparator 14 having a first input A coupled to 26 the analog sensor and a second input B coupled to the output 27 of the digital-to-analog converter 12. The output of the com-28 parator is applied as a digital or binary signal (1 or 0) to 29 the processor 10.
3 ~ ~3 1 During the calibration phase of opera~lon, ~he 2 analog sensor signal appLied to the input A o~ the comparator 3 14 is tracked by digi~al values produced by the processor 10 4 and applied to thP converter 12. For each instan~aneous S value of the analog sensor signal a~ the input A, the pro-6 cessor 10 iteratively produces a plurality of digltal values 7 until the outpu~ of the comparator 14 indicates that the 8 digital value as converted and applied to the input B is 9 equal to or corresponds with the analog sensor signal as applied to the input A. The same process is repeated for 11 subsequent instantaneous analog sensor signal values charac-12 teristic of ~he analog sensor signal which are stored in the 13 processor 10 during the calibration phase so as to permit the 14 subsequent use of that characteristic value as a sensor ref-erence to be con~erted by the converter 12 and applied to the 16 input B during the operation mode thereby providing for an 17 appropria~ely compensated analog sensor~ It will of course 18 be appreciated that the step of calibration may be repeated 19 many times and frequently so as to assure ~hat the analog sen-sor is always appropriately compensated regardless of shor~
21 term or long term drift.
22 In a particularly preferred embodiment of the in-23 vention, the analog sensor signal may be sinusoidal as shown 24 in Fig. 3A. In that case, it is desirable to store during calibration the maximum and minimum values which may then be 26 utilized to compute any of a number of reference digital values 27 for comparison with the analog sensor signal in the opera~ing 28 mode.
29 The nature of the computations which are performed 1 by the processor 10 are depic~ed in analog equivalent form 2 in the diagram of Fig. 2. A~ter the maximum and minimum 3 values of the analog sensor signals have been detected by a 4 maximum peak detec~or 16 and a minimum peak detector 18 as shown in Fig. 2, the outputs from the detectors 16 and 18 are 6 utilized by su~mers 20, 22 and 24 and constant networks 26, 7 28 and 30 so as to produce analog values at the A input to 8 the comparator 14 which correspond to 0, 30~ 45~ or 90 on 9 the sinusoidal signal depending upon the position of the angle select switch 32. The values at the switch 32 are 11 applied to the comparator 14 for comparison with the analog 12 signal during the operating mode. The ou~put from the com-13 parator corresponds with the position of the switch angle 14 (X) or (180-X~ at the output of an inverter 34.
From the foregoing, it will be unders~ood that the 16 various computation functions which are performed on an iter-17 ative basis by the processor 10 may therefore be performed by 18 an analog computer cireuit as shown in Figo 2. However, con-19 siderably more flexibility is aforded by the processor 10 Moreover, the advent of the microprocessor permits ~he compen~
21 sation of the sensor as disclosed in Figo 1 to be provided at 22 relatively low cost consistent with one important objective 23 of this invention.
24 Where the angle select switch 32 in the position shown in Fig. 2, the analog sensor signal is compared with 26 the value of the sinusoidal signal of Fig. 3A a~ 0 or (180-27 0). Utilizing the 0 point and the 180 point as the refer-28 ence produces a square wave logic signal at the output o the 29 comparator during the operate mode as shown in Fig. 3B where ~ 1fi5~
~ 6 --transitions occur at the 0 and 180 points on the analoy sensor signal.
As mentioned previously, the analog sensor signal is tracked durin~ the calibration mode as will S now be described with reference to the flow diagram of Fig. 4. In the flow diagram of ~ig, 4, it is assumed that an analog sensor of the type disclosed in Canadian application 310,368 filed August 30, 1978, assigned to the assignee of this invention, is utilized in connection with the control of a stepper motor as disclosed therein.
The sinusoidal signal produced by that sensor as shown in the waveform of Fig. 3A is produced as a result of stepping the motorO
Upon initiating calibration(40), th0 step motor of the system is moved one step forward (42) which sets a timer (44)O A loop is then entered in which the instantaneous sensor value is read (46), The reading of the sensor value is accomplished by iteratively producing digital values until the comparator output as shown in Fig. 1 produces a logic l. If the instantaneous analog sensor value is greater than the heretofore stored current maximum value (48), a new maximum value (50) is set to the current instantaneous value. On the other hand, if the instantaneous value is less than the current minimum value stored (52), a new minimum value is set in accordance with the current reading (54), If after the set ting of the maximum or minimum values(50) and (54), the timer has not yet timed out (56~, the loop is repeatedO If the timer has timed out, the maximum and minimum values which ~ ~fi~f.3gt~
1 have been set and stored are ~hen utilized to set and s~ore 2 the amplitude of the analog sensor value at the maximum 3 minus the minimum value divided by 2 (58) and the proces~or 4 exits from the calibration mode (60).
Referring now to Fig. 5, the processor may enter 6 the operate mode (62) in which the appropriate reference 7 signal is generated in accordance with the equation:
8 Re~. = (maximu= minimum)sin D + (maximum minimum) 9 where D is the reference point on the sinusoidal waveform of Fig. 3A corresponding to the angle of the switch 32 o Fig. 2.
11 The output of the comparator 14 changes state whenever ~he 12 sensor reference signal and ~he sensor signal are equal (66).
13 As noted previously, the processor during the cali-14 bration mode will produce iterative digital values until cor-re~pondence or equality is achieved between the sensor signal 16 and the digital value as co~verted by the converter 12 as 17 shown in Fig. 1. The processor may be programmed in dif~erent 18 ways to iteratively produce the digital values. For example, 19 the digital value produced at the output of the processor may be continuously incremented until equality or correspondence 21 is achieved. In the alterna~ive, the technique of SuccssSive 22 approximations may be utilized to shorten the search for the 23 corresponding digital value. Of course, the processor 10 may 24 be programmed in other ways to allow the digital values rom the processor to track the analog sensor slgnal.
26 The Fairchild F-8 microprocessor is particularly 27 well-suited for use in practicing the in~en~ion. However, the 28 processor may be o various types and siæes.
29 In the aforesaid copending application Serial No.
.
I 1 ~i5~3~3 ~3 1 310,368 the particular sensor comprises a light emik~ing 2 diode in combination with a phototransistor. As mentioned 3 previously, such a combination is relatively low cost and the 4 use of the appara~us and method disclosed herein psrmit the low cost combination ~o be utilized without any trade-off 6 with respect to drift and degradation or variations in gain 7 and offset. It will of course be appreciated that other sen-8 sors may be utilized and ~he invention is not limited ~o the 9 use of any particular type of sensor. Moreover, the inven-tion is not limited to the use o~ the method and apparatus 11 disclosed herein with respect to.any particular application 12 although the invention has been found to be extremely useful 13 in a control of stepper motors as disclosed in the aforesaid 14 copending application.
Although a particular embodiment of the invention 16 has been shown and described and various modifications have 17 been suggested~ it will be understood that the invention may 18 be incorporated in various embodiments and modifications with-19 out departing from the true spirit and scope of the invention as se~ forth in the appended claims.
Claims (7)
1. The method of using a sensor producing an analog signal with a digital processing means, comprising the following calibration steps:
converting a digital output signal from said processing means to a corresponding analog signal, comparing a sensed analog signal produced by said sensor with the-said corresponding analog signal, changing said digital output signal of said processing means in the absence of a first predetermined relationship between said sensor analog signal and said corresponding analog signal;
reiterating the foregoing steps until said first predetermined relationship exists between said sensor signal and said corresponding analog signal, repeating the foregoing steps for different instantaneous sensor analog signals to generate reference signals corresponding to at least one of the maximum amplitude, minimum amplitude and a combination of said maximum and minimum amplitudes of said sensor analog signal: and storing in said processing means information representing at least one of the digital output signals corresponding to said maximum amplitude, said minimum amplitude and said combination of said maximum and minimum amplitudes of said sensor analog signal, said method further comprising the following measuring steps:
generating a calibrated digital output signal at the output of said processing means from said at least one stored digital signal, converting said calibrated digital output signal to a calibrated analog signal value; and comparing the calibrated analog signal to an analog signal produced by said sensor; and producing a calibrated analog control signal in response to said comparison.
converting a digital output signal from said processing means to a corresponding analog signal, comparing a sensed analog signal produced by said sensor with the-said corresponding analog signal, changing said digital output signal of said processing means in the absence of a first predetermined relationship between said sensor analog signal and said corresponding analog signal;
reiterating the foregoing steps until said first predetermined relationship exists between said sensor signal and said corresponding analog signal, repeating the foregoing steps for different instantaneous sensor analog signals to generate reference signals corresponding to at least one of the maximum amplitude, minimum amplitude and a combination of said maximum and minimum amplitudes of said sensor analog signal: and storing in said processing means information representing at least one of the digital output signals corresponding to said maximum amplitude, said minimum amplitude and said combination of said maximum and minimum amplitudes of said sensor analog signal, said method further comprising the following measuring steps:
generating a calibrated digital output signal at the output of said processing means from said at least one stored digital signal, converting said calibrated digital output signal to a calibrated analog signal value; and comparing the calibrated analog signal to an analog signal produced by said sensor; and producing a calibrated analog control signal in response to said comparison.
2. A method as claimed in claim 1, wherein the sensed analog signal is substantially sinusoidal.
3. A method as claimed in claim 2, wherein the stored digital signals represent the maximum and minimum of the sinusoidal signal.
4. A method as claimed in claim 3, further including the step of computing at least one value combining digital signals to produce a signal representing sin D + , where D = the angle of said sinusoidal signal corresponding to said stored digital signal.
5. An apparatus for compensating a sensor comprising:
digital processing means;
digital-to-analog converter means having an input coupled to an output of said digital processing means, comparator means having a first input coupled to the output of said converter means, a second input adapted to be coupled to said sensor, and an output coupled to said processing means to form a closed loop, said digital processing means including means for iteratively computing digital output signals and coupling said iteratively computed digital signals to said converter means, said computing means continuing iterations until at least one of said iteratively com-puted digital signals as converted has a predetermined relationship with an instantaneous sensor output signal as determined by the output of said comparator, said digital processing means further comprising means for both iteratively producing other digital signals each having the said predetermined relationship with other instantaneous signals at said sensor output, and for storing information representing at least one of said digital signals corresponding to a maximum sensor output, a minimum sensor output and a combination of said maximum and minimum sensor outputs, so as to represent a selected characteristic of said sensor, said digital processing means further comprising means for generating a sensor calibrated digital output signal from said at least one of said digital signals corresponding to a selected characteristic of said sensor;
said converter means converting said sensor calibrated digital output signal to a calibrated analog signal; and said comparator comparing the calibrated analog signal to said sensor output;
and providing a control signal in response to said comparison.
digital processing means;
digital-to-analog converter means having an input coupled to an output of said digital processing means, comparator means having a first input coupled to the output of said converter means, a second input adapted to be coupled to said sensor, and an output coupled to said processing means to form a closed loop, said digital processing means including means for iteratively computing digital output signals and coupling said iteratively computed digital signals to said converter means, said computing means continuing iterations until at least one of said iteratively com-puted digital signals as converted has a predetermined relationship with an instantaneous sensor output signal as determined by the output of said comparator, said digital processing means further comprising means for both iteratively producing other digital signals each having the said predetermined relationship with other instantaneous signals at said sensor output, and for storing information representing at least one of said digital signals corresponding to a maximum sensor output, a minimum sensor output and a combination of said maximum and minimum sensor outputs, so as to represent a selected characteristic of said sensor, said digital processing means further comprising means for generating a sensor calibrated digital output signal from said at least one of said digital signals corresponding to a selected characteristic of said sensor;
said converter means converting said sensor calibrated digital output signal to a calibrated analog signal; and said comparator comparing the calibrated analog signal to said sensor output;
and providing a control signal in response to said comparison.
6. An apparatus as claimed in claim 5, wherein said digital processing means provides at least two of said digital signals to generate said sensor calibrated digital output signal corresponding to a selected characteristic of said sensor.
7. An apparatus as claimed in claim 5, wherein said digital processing means provides at least one digital signal from said at least one stored digital signal to generate said sensor calibrated digital output signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US873,596 | 1978-01-30 | ||
| US05/873,596 US4198677A (en) | 1978-01-30 | 1978-01-30 | Method and apparatus for compensating a sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165888A true CA1165888A (en) | 1984-04-17 |
Family
ID=25361955
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000320500A Expired CA1165888A (en) | 1978-01-30 | 1979-01-30 | Method and apparatus for compensating a sensor |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US4198677A (en) |
| JP (1) | JPS54118262A (en) |
| AU (1) | AU4376279A (en) |
| BE (1) | BE873779A (en) |
| BR (1) | BR7900533A (en) |
| CA (1) | CA1165888A (en) |
| DE (1) | DE2903194A1 (en) |
| FR (1) | FR2415828B1 (en) |
| GB (1) | GB2013434B (en) |
| IT (1) | IT1110799B (en) |
| NL (1) | NL7900748A (en) |
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-
1978
- 1978-01-30 US US05/873,596 patent/US4198677A/en not_active Expired - Lifetime
-
1979
- 1979-01-27 DE DE19792903194 patent/DE2903194A1/en not_active Withdrawn
- 1979-01-29 BR BR7900533A patent/BR7900533A/en unknown
- 1979-01-29 IT IT19687/79A patent/IT1110799B/en active
- 1979-01-29 FR FR7902240A patent/FR2415828B1/en not_active Expired
- 1979-01-30 BE BE2/57576A patent/BE873779A/en not_active IP Right Cessation
- 1979-01-30 JP JP884679A patent/JPS54118262A/en active Pending
- 1979-01-30 AU AU43762/79A patent/AU4376279A/en not_active Abandoned
- 1979-01-30 CA CA000320500A patent/CA1165888A/en not_active Expired
- 1979-01-30 GB GB7903105A patent/GB2013434B/en not_active Expired
- 1979-01-30 NL NL7900748A patent/NL7900748A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| IT1110799B (en) | 1986-01-06 |
| GB2013434A (en) | 1979-08-08 |
| IT7919687A0 (en) | 1979-01-29 |
| FR2415828B1 (en) | 1985-06-07 |
| BE873779A (en) | 1979-07-30 |
| US4198677A (en) | 1980-04-15 |
| FR2415828A1 (en) | 1979-08-24 |
| BR7900533A (en) | 1979-08-21 |
| GB2013434B (en) | 1982-07-28 |
| AU4376279A (en) | 1979-08-09 |
| JPS54118262A (en) | 1979-09-13 |
| NL7900748A (en) | 1979-08-01 |
| DE2903194A1 (en) | 1979-10-31 |
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