Turning device position sensing system and method

A system for determining an absolute position of a motor. The system includes first and second multi-polar magnetic rings, first and second processing units, and at least one external sensor. The first multi-polar magnetic ring is concentrically positioned around the motor, and has a plurality of pole pairs. The second multi-polar magnetic ring is concentrically positioned around the first multi-polar magnetic ring, and has at least one pole pair. The first processing unit is positioned near the first multi-polar magnetic ring to determine an angular position over one of the pole pairs of the first multi-polar magnetic ring. The sensor is positioned external to the processing unit and over the second multi-polar magnetic ring to indicate a state of the pole pair of the second multi-polar magnetic ring. The second processing unit generates an absolute position of the motor based on the angular position and the state.

FIELD

Embodiments of the invention relate generally to sensing systems and methods, and particularly to sensing system controls.

BACKGROUND

In many motor applications, positions of the motor are sensed. Once motor positions are sensed, power can be applied to operate these motors accordingly. Different applications have different motor phase sensing requirements. For example, the Timken Company's MPS160 can be used to determine an absolute position of a target magnet. However, chips such as the MPS160 typically can only be used to determine the absolute position of the target within each North (N)/South (S) pole pair only. These pole pairs can be up to 6 mm wide in some performance configurations. Furthermore, to cover ⅓, ¼, or ⅕ of a revolution, a very large single absolute position sensor chip may be required. A large single absolute position sensor can be difficult to apply in many applications, such as those that have a space limitation.

There are several application-specific-integrated-circuits (“ASIC's”) collectively referred to as motor sensors, that can be used to sense positions of a motor. For example, Timken's MPS32XF produces high resolution signals from a wide range of magnetic pole widths. This motor sensor is programmable and equipped with a Hall sensor array.

In some steering wheel applications, for example, in order to accurately control or activate a steering column, an absolute steering column position is needed over multiple turns of the steering wheel or column. To determine an absolute steering column position, some controllers will combine outputs of a turn counter with a position signal of a steering wheel over one revolution as provided by a sensing device. However, implementing a turn counter can be costly and can increase complexity of the sensing device.

SUMMARY

In one form, the invention provides a system for determining an absolute position of a motor. The system includes first and second multi-polar magnetic rings, first and second processing units, and at least one external sensor. The first multi-polar magnetic ring is concentrically positioned around the motor, and has a plurality of pole pairs. The second multi-polar magnetic ring is concentrically positioned around the first multi-polar magnetic ring, and has at least one pole pair. The first processing unit is positioned near the first multi-polar magnetic ring to determine an angular position over one of the pole pairs of the first multi-polar magnetic ring. The at least one sensor is positioned external to the processing unit and over the second multi-polar magnetic ring to indicate a state of the at least one pole pair of the second multi-polar magnetic ring. The second processing unit generates an absolute position of the motor based on the angular position and the state.

In another form, the invention provides a sensing system for determining an absolute position of a turning device. The sensing system includes first magnetic and second multi-polar magnetic rings, first and second processing unit, and first and second sensors. The first multi-polar magnetic ring is concentrically positioned around the turning device, and has a plurality of pole pairs to rotate with the turning device. The second multi-polar magnetic ring is positioned around the first multi-polar magnetic ring, has at least one pole pair and is configured to rotate with the first multi-polar magnetic ring and the turning device. The first processing unit is positioned near the first multi-polar magnetic ring to determine an angular position of the turning device based on one of the pole pairs of the first multi-polar magnetic ring. The first sensor is positioned external to the first processing unit and adjacent the second multi-polar magnetic ring to indicate a first state of the at least one pole pair of the second multi-polar magnetic ring. The second sensor is positioned external to the first processing unit, adjacent the second multi-polar magnetic ring, and spaced apart from the first sensor to indicate a second state of the at least one pole pair of the second multi-polar magnetic ring. The second processing unit generates the absolute position of the turning device based on the angular position and the first and second states.

In still another form, the invention provides a method of determining an absolute position of a turning device with a first multi-polar magnetic ring concentrically positioned around the turning device, a second multi-polar magnetic ring concentrically positioned around the first multi-polar magnetic ring, a processing unit positioned over the first multi-polar magnetic ring, and at least one sensor positioned near the processing unit and over the second multi-polar magnetic ring. The method includes determining with the processing unit a local pole position of the first multi-polar magnetic ring, determining from the at least one sensor at least one state of the second multi-polar magnetic ring, and determining from the at least one state and the local pole position an absolute position of the turning device.

DETAILED DESCRIPTION

As should also be apparent to one of ordinary skill in the art, the systems shown in the figures are models of what actual systems might be like. As noted, many of the modules and logical structures described are capable of being implemented in software executed by a microprocessor or a similar device or of being implemented in hardware using a variety of components including, for example, application specific integrated circuits (“ASICs”). Terms like “processing unit” may include or refer to both hardware and/or software. Furthermore, throughout the specification capitalized terms are used. Such terms are used to conform to common practices and to help correlate the description with the coding examples and drawings. However, no specific meaning is implied or should be inferred simply due to the use of capitalization. Thus, the claims should not be limited to the specific examples or terminology or to any specific hardware or software implementation or combination of software or hardware.

As described earlier, sensing ASICs such as MPS160 chips are capable of determining the absolute position of a target magnet within one North/South pole pair only; however, these pole pairs can be up to 6 mm wide in certain high performance configurations.

In one form, the invention provides a method of determining an absolute position of a motor over each motor phase for a motor position sensing controller. The method involves combining absolute position information that is accurate and specific to a North/South pole pair with coarse information that is indicative of position relative to the entire Hall string. Accordingly, absolute position across the Hall string can be accurately determined.

In one embodiment, the method includes attaching one or more digital Hall sensors to the motor position sensing system to produce an absolute position signal over 2 or more pole pairs. The method also includes routing signal outputs from the attached sensors through the motor position sensing controller, and relaying the signal outputs via a data link.

In another form, the invention provides a system for determining an absolute position of a motor over each motor phase. The system includes a digital Hall sensor, a motor position sensing controller, and a data link. The digital Hall sensor is attached to the motor position sensing controller to produce an absolute position signal over 2 or more pole pairs. The attached sensor routes signal outputs through the motor position sensing system, and relays the outputs via the data link.

Timken's MPS32XF or other suitable sensor can be programmed to disable Hall cells on both ends of the Hall sensor array to properly match effective pole width of the motor sensor to the width of the target magnet poles. The number of Hall sensors used in the Hall sensor array varies from application to application. For instance, all of the Hall sensors are utilized when the target magnet pole width matches the total pole width offered by the Hall sensors. However, at times, the target magnet pole width does not match the total width offered by the Hall sensors. For example, a small number of poles are matched when only a portion of Hall sensors in the Hall sensor array are used. In such cases, there is a reduced signal-to-noise ratio (“SNR”) because a reduced signal strength is produced by the Hall sensor array.

In another form, the invention provides a method and system of matching a pole width of a Hall sensor array with a pole width of a target magnet. Embodiments of the invention operate a sensing controller with all sensing elements in the array, or only a portion of the array. For example, the MPS32XF sensor has 16 Hall sensor elements. In some embodiments, the MPS32XF sensor can use 16 Hall elements or reduce the number of Hall elements to 12 or 8 by disabling the Hall elements on ends of the array. For small poles when only a portion of the Hall array is used, there is a reduced SNR because there a smaller signal produced by the Hall array.

In one particular embodiment, the invention describes a method that involves attaching one, two, or three digital Hall sensors to an MPS160 or similar chip to produce an absolute position signal over 2, 3, 4, or 5 pole pairs. The signals from these external sensors can be routed through an ASIC and provided to an external system via a serial data link. This sensor and magnet configuration can fulfill the requirements of many motor applications.

For example,FIG. 1shows a first exemplary absolute position sensing system100for a motor104having an armature, shaft, or rotor108, and a stator112. In the embodiment shown, the stator112has four magnetic segments or arcs116. Each of the segments116contains a magnetic pole pair, and occupies an arc of about 90°, which is one-quarter (¼) of a revolution (360°). As such, the motor104as shown is a 4-pole motor.

The first sensing system100includes a first multi-polar magnetic ring or high resolution track120, which includes 12 magnetic pole pairs. It should be noted that only the high resolution track120of one of the segments116is shown. As such,FIG. 2only shows three magnetic pole pairs. The high resolution track120is concentrically positioned with respect to the rotor108. A second multi-polar magnetic ring or a low resolution track124concentrically encompasses the high resolution track120. In the embodiment shown, the low resolution track124includes four magnetic pole pairs. It should be noted that the high resolution track120can have more or less magnetic pole pairs in other embodiments. Similarly, the low resolution track124can have more magnetic pole pairs in other embodiments

Furthermore, the first sensing system100includes a processing unit128that is positioned over the stator112, the high resolution track120, and the low resolution track124. An exemplary processing unit is a Timken sensor MPS160, which can generate signals that indicate one out of 160 angular positions over one of the pole pairs of the high resolution track120, and a reference pulse signal that indicates a center position. In some embodiments, the processing unit128includes an interface132for interfacing with components external to the processing unit128. In other embodiments, the interface132is external to the processing unit128. The processing unit128also includes an internal sensor array136to generate an output that is indicative of an angular position of a pole pair under the processing unit128. It should be appreciated that the internal sensor array136can include a string of sensing elements such as Hall effect sensors. The first sensing system100also includes a first external sensor140that is positioned over the low resolution track124. In the embodiment shown, the first external sensor140is a Hall effect sensor. Additionally, the first sensing system100also includes a second external sensor144that is positioned over the low resolution track124. Particularly, the second external sensor144is positioned less than or about 90° from the first external sensor140. In the embodiment shown, the second external sensor144is also a Hall effect sensor.

In general, a number of pole pairs used in the high resolution track120used in a particular application determines a number of external sensors needed. In the embodiment shown, since there are three pole pairs to be identified, a number of low resolution pole pairs is one, and since only one of the three pole pairs will activate a particular external sensor, only a total of two external sensors are necessary. Two external sensors will generally provide a total of four logically unique combinations. For example, when an output of the first external sensor140is inactive and an output of the second external sensor144is inactive, neither of the first and second external sensors140,144are active, or both are in an OFF state. Similarly, when the output of the first external sensor140is inactive and the output of the second external sensor144is active, the first external sensor140is in an OFF state, while the second external sensor144is in an ON state. For another example, if the number of pole pairs used in the high resolution track120is five times the number of pole pairs used in the low resolution track124, a total of three external sensors will be necessary. In some embodiments, an additional sensor will also be used in conjunction with the determined number of external sensors due to tolerance issues such as magnet alignment.

A second processing unit148receives data or information indicative of the state signals and the angular signals from the first and second external sensors140,144, and the processing unit128, respectively, through the interface132. In some embodiments, the data or information is received in the form of a serial data signal via a serial data interface. The second processing unit148then processes the received data or information and generates an absolute position of the motor104, detailed hereinafter.

FIG. 2shows a plurality of external sensor outputs200with respect to the high resolution pole pairs120ofFIG. 1. Particularly, outputs of the first external sensor140due to one of the corresponding pole pairs208is shown in waveform204, while outputs of the second external sensor144, which is positioned about 90° from the first external sensor140, is shown in waveform210. For example, when the first external sensor140is low, and the second external sensor144is low, the second processing unit148generates a signal that is indicative of a target pole pair being pole pair N1, S1.

In operation, the data from the processing unit128is received at the second processing unit148. The data contains local absolute position information over one North-South pole pair of the motor104. The data also contains the state of the raw reference pulse (“Rp”) signal and the state of each external Hall sensor140,144. If the data from the example shown inFIG. 2with two external Hall sensors140,144, and three high resolution pole pairs120per motor segment116are read, the second processing unit148or a user can use the information from the two external Hall sensors140,144to determine if the absolute position reading was from the 1st, 2nd, or 3rd, North/South high resolution pole pair120in the corresponding segment116. This is possible since the two external Hall sensors140,144produce four states, and the user or the second processing unit148only needs to properly identify which one of the three high resolution pole pairs120is being reported in the absolute position data. For example, Timken's MPS160 can generate a number between 1 to 160 to indicate an angular position of one of the high resolution pole pairs. As such, when the MPS160 is used with a 4-pole motor with 12 high resolution pole pairs, the MPS160 generates an angular position of 80, which indicates of about 45° at a corresponding high resolution pole pair. Accordingly, if the second processing unit148determines that the angular position originates from the second high resolution pole pair in a corresponding segment, an absolute position can be obtained from the angular position of about 80 and the second pole pair (each pole pair being able to generate 160 positions). In such a case, the second processing unit148will determine that the absolute position is 240, which is a sum of 80 and 160.

FIG. 3shows a second exemplary absolute position sensing system300for a motor304having an armature, shaft, or rotor308, and a stator312. In the embodiment shown, the stator312has four magnetic segments or arcs316; thus, the motor304is a 4-pole motor. The second sensing system300includes a first multi-polar magnetic ring or high resolution track320, which includes eight magnetic pole pairs. It should be noted that only the high resolution track320of one of the segments316is shown. As such,FIG. 3only shows two magnetic pole pairs. The high resolution track320is concentrically positioned with respect to the rotor308. A second multi-polar magnetic ring or low resolution track324having four pole pairs concentrically encompasses the high resolution track320.

The second sensing system300includes a processing unit328positioned over the stator312, the high resolution track320, and the low resolution track324. Like the processing unit128ofFIG. 1, the processing unit328also includes an optional interface332for interfacing with components external to the processing unit328, and an internal sensor array336to generate an output that is indicative of an angular position of a pole pair under the processing unit328. The second sensing system300also includes an external sensor340that is positioned over the low resolution track324. In the embodiment shown, the external sensor340is a Hall effect sensor.

As indicated earlier, the number of pole pairs used in the high resolution track320used in a particular application generally determines the number of external sensors needed. In the embodiment shown, since there are two pole pairs to be identified, and since only one of the two pole pairs will activate the external sensor340, only one external sensor is thus necessary. Particularly, one external sensor will generally provide a total of two logically unique combinations. For example, when an output of the external sensor340is inactive, the external sensor340is in an OFF state. Conversely, when the output of the external sensor340is active, the external sensor340is in an ON state.

A second processing unit348then receives data or information indicative of the state and the angular signals from the external sensor340and the reference pulse signals from the processing unit328, respectively, through the interface332. As discussed earlier, the data or information can be received in the form of a serial data signal via a serial data interface. The second processing unit348then processes the received data or information and generates an absolute position of the motor104, detailed hereinafter.

FIG. 4shows an output waveform400generated by the external sensor340with respect to the high resolution pole pairs320ofFIG. 3. Due to tolerance issues relating to magnet precision and alignment, the reference pulse signals from the processing unit328are also used in the second processing unit348to determine the absolute position. In such a case, the reference pulse waveform404is also shown.

Particularly, in the case of two high resolution pole pairs320per motor segment316, a proper identification of the high resolution pole pair320can be accomplished by using only the external Hall sensor340if the internal reference pulse signal from the processing unit328is aligned with a transition of the external Hall sensor340. In such a case, the external Hall sensor340will be in an ON state for every other North to South transition of the high resolution track320. In this case, the second processing unit348reads the local absolute angular position, and then determines which high resolution pole pair320is being read by the processing unit328by reading the reference pulse signal and the external Hall sensor signal400.

FIG. 5shows a Hall sensor array arrangement500that can be incorporated into the sensing systems100,300ofFIG. 1andFIG. 3. Particularly, the arrangement500shows a total of 16 Hall sensors504having a width W. However, in some embodiments, only a portion of the arrangement500, for example, 25 percent, is used.FIG. 6shows an example in which only a portion of the arrangement500is used. In such cases, signals generated by the arrangement500will have a low signal-to-noise ratio (“SNR”). For example, since the sensors504generate quadrature signals such as sine and cosine, a 25 percent reduction effectively reduces the arrangement500to about half its original length. For example, as shown inFIG. 6, an interior set of sensors508for sine signals are used, while an exterior set of sensors512are not used. An interior set of sensors516for cosine signals are used, while an exterior set of sensors520are not used.

To increase the SNR of the generated sensor signal, and thus to allow the arrangement to produce usable signals from the Hall sensor array, outputs of the remaining portions of the Hall sensors504are duplicated as follows.FIG. 7shows a dual full period Hall sensor configuration700of the Hall sensor array arrangement500ofFIG. 5. Particularly, for the sine signals, the outputs of the interior sensors508are mirrored at the exterior sensors512as shown in704. For the cosine signals, signs of the interior sensors516are reversed at the exterior sensors520as shown in708.

Embodiments described herein have various advantages. For example, an increased signal strength can be achieved by using the signal from twice the number of Hall sensors as in a traditional design. This can also allow for a weaker magnetic target or a larger air gap between a standard magnet and the sensor. If the same air gap is used, the signal will have a better signal to noise ratio, which is beneficial to accuracy. Using twice the number of Halls can produce a more consistent signal as the effect of any offset or gain errors in individual Halls is reduced. Using twice the number of Halls also produces a higher SNR.

Embodiments of the invention are applicable, for example, in a vehicular environment.FIG. 8shows a schematic plan view of a motor vehicle800having a steering wheel sensing system804and turning in a direction indicated by arrow808. The vehicle800has four wheels812A,812B,812C, and812D. The steering wheel sensing system804determines how many revolutions a driver has rotated a steering column816with respect to a fixed location. For example, in some embodiments, the steering wheel sensing system804can determine an absolute steering column position over three, four, or five turns of the steering wheel or column816. In the embodiment shown, the vehicle800travels in the direction808by rotating the wheel812A at a speed of s1, and the wheel812B at a speed of s2. In general, when turning, the speed of s1and the speed of s2are different, and hence there is a speed differential of the wheels812A and812B.

Instead of using a traditional turn counter,FIG. 9shows a cross-sectional view of the steering sensing system804ofFIG. 8according to an embodiment of the invention by combining a local absolute position as described earlier, and the speed differential. Particularly,FIG. 9shows that the steering sensing system804surrounds the steering column816. Some components of the steering sensing system804are configured to rotate with the steering column816. For example, the steering sensing system804includes a first multi-polar magnetic ring or high resolution track820and a multi-polar magnetic ring or low resolution track824concentrically encompassing the high resolution track820.

Furthermore, the steering sensing system804also includes a processing unit828that is positioned over the high resolution track820, and the low resolution track824. In some embodiments, the processing unit828includes an interface832for interfacing with components external to the processing unit828. The processing unit828also includes an internal sensor array836to generate an output that is indicative of an angular position of a high resolution pole pair under the processing unit828. The steering sensing system804also includes a first external sensor840that is positioned over the low resolution track824, and a second external sensor844that is also positioned over the low resolution track824. In the embodiment shown, the exemplary high resolution track has 12 pole pairs, while the exemplary low resolution track820has four pole pairs. In such a case, the second external sensor844is positioned less than or about 90° from the first external sensor840.

Similar to the embodiments described above, for example, by combining an absolute position within each segment of a rotation (determined with external sensors) and the speed differential speed signal from the front wheels812A and812B, the steering sensing system804uses a second processing unit848to determine a full absolute position over several turns of the steering wheel816. Particularly, the differential speed determined from the front wheels812A,812B is used to isolate which of all possible 90° segments or sections the steering wheel816is in. With a typical steering system such as a 3-turn-lock-to-lock system or a 4-turn-lock-to-lock system, each turn consisting of four 90°-sections, the steering wheel816can thus be in 12 to 16 different 90° sections. Although only the front wheels812A,812B are described herein, the speeds and directions of the rear wheels812C,812D can also be used in other embodiments.

In some embodiments, a ratio of the speeds (s1, s2) between the wheels812A,812B changes in proportion to a position of the steering wheel816. As described above with respect to the motor104ofFIG. 1, the steering sensing system804identifies the absolute position of a steering wheel816(or its associated steering column) by using a unique combination of the reference pulse signals generated by the processing unit828.

For example, as discussed earlier, the steering sensing system804uses a local angular position detected by the processing unit828, segment information detected or identified by the external sensors840,844, and differential speed information detected by a plurality of wheel sensors, to generate an absolute position of the steering column816that generally repeats multiple times in a revolution. Particularly, the steering sensing system804uses the differential speed information from the front wheels812A,812B to identify one of the segments816in a multiple-turn-lock-to-lock steering system. By adding the unique reference pulses generated from the processing unit828for each of the segments816, a full absolute position within a revolution can be determined without turning the steering column for more than half of a segment. For example, with a four-segment steering wheel816and a reference pulse configuration, a reference pulse indicative of a specific segment is generated for each of the four segments within a revolution. As such, a full absolute position within each revolution can be determined by turning the steering wheel816a maximum of 45°. That is, once the steering wheel816has turned about 45°, the steering wheel816has crossed into another quadrant, and a reference pulse is generated.

Furthermore, after rotating the steering wheel816for about 30°, the differential signal from the front wheels812A,812B can be identified with the reference pulses in each of the segments816, detailed hereinafter. For example, if the resolution of the speeds detected from the front wheels812A,812B is too coarse or not precise enough, or if one of the front wheels812A,812B is slipping on sand, the processing unit828can generate reference pulses while the steering wheel816is turned. As such, if the second processing unit848is uncertain about positions of the wheels812A,812B due to the above or similar conditions, the reference pulses from each of the segments816can be used to identify the segment816.

FIG. 10shows a plurality of exemplary reference pulse patterns1000in a 4-quadrant embodiment. For example, when there is a change from a North pole to a South pole in a pole pair, a C reference pulse is generated in a corresponding quadrant. Similarly, when there is a change from a South pole to a North pole in a pole pair, a D reference pulse is generated in a corresponding quadrant. Otherwise, when there is no pole change, a 0 reference pulse is generated. As shown inFIG. 10, there is no change in a first quadrant1004. There are North to South pole changes in a second quadrant1008. Similarly, there are both North to South and South to North pole changes in the third quadrant1012, while there are only South to North pole changes in the fourth quadrant1016.