Patent Description:
The present invention relates to position sensing systems and methods.

Various absolute position sensors and associated signal processing techniques are known for determining an absolute position of a rotating or linearly-moving target. For example, <CIT> discloses one such example of an off axis magnetic sensor that uses a two-track, multi-pole magnetic target with evenly-spaced and sized high resolution magnetic poles. The <NUM> Patent describes how to use a high resolution Hall effect sensor like the Timken MPS <NUM> or MPS512 sensor chip to detect local absolute position over a magnetic pole pair. The <NUM> Patent shows how to use a second track with one or more pole pairs to generate a coarse or low resolution absolute position signal that can then be used together with a high resolution Hall effect sensor like the Timken MPS160 or MPS512 sensor chip to determine a fine or high resolution absolute position over a longer arc or longer linear range. Other sensors are known, such as <CIT> or <CIT>, which each disclose a digital absolute position encoder.

Also known is the use of Gray code encoding on magnetic encoders. Gray code encoding is a system of binary counting in which any two adjacent codes differ by only one bit position. It is possible to arrange several sensors adjacent a single track (ring or linear) so that consecutive positions differ at only a single sensor. The result is the single-track Gray code encoder. This concept can be used for the reference track of the encoder described in the '<NUM> Patent such that the signal from the reference-track Gray code can be combined with the signal from the high resolution Hall effect sensor, processed using software on the processor, and then outputted as a fine or high resolution absolute position signal.

The present invention contemplates improvements to the sensor arrangements and signal processing described above. The scope of the invention is defined in appended claim <NUM>. In one embodiment, the latency or processing time conventionally required to repeatedly or continuously calculate the fine or high resolution absolute position with conventional software and processors can be greatly reduced. Conventionally, the processing chip, which can be internal or external to the high resolution sensor or incorporated into the high resolution sensor, must repeatedly combine and process the output signal from the reference track with the output signal from the high resolution track to determine the fine absolute position. According to one embodiment of the present invention, after the initial fine absolute position calculation is completed one time by the processing chip, the system then uses an up/down count signal to continuously, or on demand, update the full absolute position reading without any further software processing. The absolute position is maintained in an up/down hardware counter. Such a hardware counter can increment or decrement independently of any software. This results in a fine or high resolution absolute position output signal that is achieved more quickly and efficiently than conventional software-generated signals, as it is delayed only by the logic timing associated with the up/down counter for each change in position, and not by any processing times associated with the software or processor.

In another embodiment, the resolution of encoders utilizing a single-track Gray code arrangement can be improved via modification. A third track is added to further subdivide the number of positions that can be determined by the single-track Gray code arrangement of the reference track. When combined with the signal from the high-resolution track and the reference track, the encoder can achieve an increased resolution.

In another embodiment, the resolution of encoders utilizing a single-track Gray code arrangement can be improved via a different modification. The inventive reference track is configured with a modified single-track Gray code that defines <NUM> or more distinct segments of the reference track (ring or linear), each segment having its own Gray code (which can all be the same Gray code or different Gray codes). A third track is then added and can be used to identify each distinct Gray code segment to construct higher resolution absolute position detection over one revolution or length of the encoder. The use of multiple Gray code segments on the reference track also enables a reduction in the physical space needed for the Hall array associated with the reference track, and can also help to reduce the overall system cost.

Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting.

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.

<FIG> illustrate an example of an absolute position sensing system <NUM> that does not form part of the invention. With reference to <FIG>, this sensing system <NUM> includes a first multi-polar magnetic ring or high resolution track <NUM>, which includes twenty-five magnetic pole pairs or North/South pole pairs. Each pole of each North/South pole pair is the same size (e.g., arc length). A second multi-polar magnetic ring or a reference track <NUM> is positioned concentrically within the high resolution track <NUM>. In the example shown, the reference track <NUM> includes four magnetic pole pairs or North/South pole pairs. The illustrated pole pairs of the reference track <NUM> are arranged to define what is known as a single-track Gray code. Gray encoding is a system of binary counting in which any two adjacent codes differ by only one bit position. It is possible to arrange several sensors adjacent to a single track (ring or linear) so that consecutive positions differ at only a single sensor, thereby allowing the sensor array to determine an absolute position about the single-track Gray code segment. As shown in <FIG>, the single-track Gray code configuration is a single segment that extends over the entire arc length of the circular reference track <NUM>. <FIG> illustrates the Gray code segment of the reference track <NUM> stretched linearly, and illustrates how an array of <NUM> Hall effect sensors can determine a coarse position among <NUM> possible positions along the single-track Gray code segment. As will be explained below, other examples can include a reference track having two or more single-track Gray code segments that together extend over the <NUM> degree arc length of the reference track.

It should be noted that the high resolution track <NUM> can have more or fewer magnetic pole pairs in other embodiments. Similarly, the reference track <NUM> can have more or fewer magnetic pole pairs in other embodiments. Additionally, the orientation of the reference track <NUM> being within the high resolution track <NUM> could be reversed, such that the reference track <NUM> is outside the high resolution track <NUM>. Furthermore, while shown as circular tracks, those skilled in the art will understand that parallel linear tracks could be used instead of concentric or radial circular tracks.

<FIG> illustrates the sensors associated with the high resolution track <NUM> and the reference track <NUM> of <FIG>. The tracks <NUM>, <NUM> are shown schematically in <FIG> without the pole pairs illustrated. A sensor and processing unit <NUM> is associated with the high resolution track <NUM> and is configured to determine a position of the device over one of the North/South pole pairs of the high resolution track <NUM>. The processing unit <NUM> takes the form of a sensing ASIC, such as a Timken MPS160 or MPS512 chip, and is capable of determining the absolute position of a target magnet within one North/South pole pair of the high resolution track <NUM> only. The processing unit <NUM> can also generate a reference pulse signal that indicates a center position of the one North/South pole pair. The processing unit <NUM> includes an internal sensor array <NUM> (see <FIG>) to generate an output that is indicative of an angular position of a pole pair under the processing unit <NUM>. It should be appreciated that the internal sensor array <NUM> can include a string of sensing elements such as Hall effect sensors. It should be understood that the processing unit <NUM> can include an optional interface for interfacing with components external to the processing unit <NUM>.

An array of Hall effect sensors <NUM> is associated with the reference track <NUM> and is configured to determine a coarse absolute position of the device over the single-track Gray code segment and to output a reference signal to the processing unit <NUM> indicative of the coarse absolute position of the device over the single-track Gray code segment of the reference track <NUM>. While six Hall effect sensors are shown in the array <NUM>, other embodiments can use different numbers of sensors. The distance between adjacent sensors <NUM> can be equal, but can be longer than a pole length of one or more poles on the reference track <NUM>. With the coarse absolute position determined by the reference track <NUM>, the processing unit <NUM> combines the reference signal with the position of the device over one of the North/South pole pairs of the high resolution track <NUM> to determine an initial, fine absolute position of the device. For a rotary encoder, this can be an absolute mechanical angle/angular position of a target/target wheel.

After the initial fine absolute position calculation is completed one time by the sensor and processing unit <NUM>, the system <NUM> then uses an up/down count signal to continuously, or on demand, update the fine absolute position reading without any further software processing. <FIG> schematically illustrates this usage of an up/down data counter. As shown in <FIG>, the initial fine absolute position of the device is represented in box <NUM>. In some embodiments, the initial absolute value represented in box <NUM> could be the summation of the detected initial absolute value plus an offset value specific to a customer application. In this manner, the start position (e.g., <NUM> position) of the absolute encoder can be set for a specific customer application. This offset capability can alternatively be achieved in the manner discussed below with respect to <FIG>. This initial absolute value <NUM> is loaded into an up/down counter <NUM> (which can be a Quadrature Counter or a Quadrature decoder with an up/down counter). The up/down counter <NUM> is incremented or decremented independently of any software using the A and B high-resolution quadrature signals <NUM> associated with the high resolution track <NUM>. The output from the up/down counter <NUM> can be of any typical architecture or format for parallel or serial output, such as SPI. The output from the up/down counter <NUM> provides absolute results indicative of the fine absolute position, without any further software-based processing, to maintain and continuously update the fine absolute position of the device. This results in a fine or high resolution absolute position output signal that is achieved more quickly and efficiently than conventional software-generated signals, as it is delayed only by the logic timing associated with the up/down counter <NUM> for each change in position, and not by any processing times associated with software or a processor.

As an alternative to using the A and B high-resolution quadrature signals <NUM> to increment/decrement the counter <NUM>, the input to the counter <NUM> could be pulse and direction signals from the high resolution track <NUM>, as shown in <FIG>.

In one application, a signal generated by the up/down counter <NUM> is further processed (e.g., by an additional logic circuit) to generate a low resolution signal or signals, such as three low resolution square wave signals with a <NUM> degree difference, which can be used for motor commutation detection and control. These commutation signals for motor control, based on the absolute position value from the up/down counter <NUM>, are as accurate as a high resolution signal, more accurate than the conventional method that uses hall sensors to directly detect coarse/reference track transition edges, and provides a faster response as compared to software-generated commutation signals.

<FIG> illustrates a process for verifying the data output from the up/down counter <NUM>. More specifically, it illustrates an operation that can be repeated at a lower frequency to constantly monitor whether the counter output agrees with the fine absolute position or angle calculation. Sometimes static discharges, such as nearby lightning strikes, can negatively impact the up/down counter <NUM>. To verify the accuracy of the counter's output, periodic checking can occur. As shown in <FIG>, the fine absolute position can be re-calculated at block <NUM> in the same manner as described above for the initial, fine absolute position <NUM> calculation. This re-calculated value can be compared with the actual output from the counter <NUM> at block <NUM>. If there is a confirmed mismatch indicating the counter <NUM> has a wrong value, the counter <NUM> will be reloaded with the new counter initial value. An alarm can also be used to notify of the mismatch/error. This process can be utilized with any of the absolute position sensing systems described herein.

<FIG> illustrates a first absolute position sensing system <NUM> according to the claimed invention. The first sensing system <NUM> includes a first multi-polar magnetic ring or high resolution track <NUM>, which includes sixty-four magnetic pole pairs or North/South pole pairs. Each pole of each North/South pole pair is the same size (e.g., arc length). A second multi-polar magnetic ring or a reference track <NUM> is positioned concentrically within the high resolution track <NUM>. In the embodiment shown, the reference track <NUM> includes three magnetic pole pairs or North/South pole pairs arranged to define a single-track Gray code.

A sensor and processing unit <NUM> is associated with the high resolution track <NUM> and is configured to determine a position of the device over one of the North/South pole pairs of the high resolution track <NUM>. The sensor and processing unit <NUM> takes the form of a sensing ASIC, such as a Timken MPS160 or MPS512 chip, and is capable of determining the absolute position of a target magnet within one North/South pole pair of the high resolution track <NUM> only. An array of Hall effect sensors <NUM> is associated with the reference track <NUM> and is configured to determine a coarse absolute position of the device over the single-track Gray code segment and to output a reference signal to the processing unit <NUM> indicative of the coarse absolute position of the device over the single-track Gray code segment of the reference track <NUM>. The distance between adjacent sensors <NUM> can be equal, but can be longer than a pole length of one or more poles on the reference track <NUM>. The single-track Gray code of the reference track <NUM>, when combined with the array of five Hall effect sensors <NUM>, can provide thirty coarse positions. However, thirty positions are not enough to provide the fine absolute position because the high resolution track includes sixty-four pole pairs.

In order to increase the resolution for the sixty-four pole pairs of the high resolution track <NUM>, a third track or second reference track <NUM> is provided. As illustrated in <FIG>, the third track <NUM> is located concentrically between the high resolution track <NUM> and the reference track <NUM>, and includes sixteen North/South pole pairs, with each pole of each North/South pole pair being the same size (e.g., arc length). The arc length of each pole pair of the third track <NUM> encompasses four pole pairs of the high resolution track <NUM>. In this manner, the thirty course positions identifiable by the reference track <NUM>, in combination with the output from the third track sensors <NUM>, can identify the fine absolute position over 4x16 = <NUM> pole pairs of the high resolution track <NUM>. If using a nine bit high-resolution interpolator, the encoder output will be <NUM>, <NUM>,. , <NUM> x <NUM>^<NUM>-<NUM>. An array of Hall effect sensors <NUM> (three sensors are shown) is associated with the third track <NUM> and communicates with the processing unit <NUM>. This system <NUM> can avoid using very small (narrow/short arc length) North/South pole pairs, so as to allow using low cost sensors (such as Hall switch sensors) for the reference track <NUM> and the third track <NUM>, while still achieving increased resolution as compared to the sensing system <NUM> illustrated in <FIG>. It should be noted that the respective positions of the tracks (i.e., inside or outside of one another) can be varied from the illustrated embodiment.

<FIG> illustrates a second absolute position sensing system <NUM> that provides even higher resolution than the first system <NUM>. The second sensing system <NUM> includes a first multi-polar magnetic ring or high resolution track <NUM>, which includes one hundred twenty-eight magnetic pole pairs or North/South pole pairs. Each pole of each North/South pole pair is the same size (e.g., arc length). A second multi-polar magnetic ring or a reference track <NUM> is positioned concentrically within the high resolution track <NUM>. In the embodiment shown, the reference track <NUM> includes four magnetic pole pairs or North/South pole pairs arranged to define a single-track Gray code.

A sensor and processing unit <NUM> is associated with the high resolution track <NUM> and is configured to determine a position of the device over one of the North/South pole pairs of the high resolution track <NUM>. The processing unit <NUM> takes the form of a sensing ASIC, such as a Timken MPS160 or MPS512 chip, and is capable of determining the absolute position of a target magnet within one North/South pole pair of the high resolution track <NUM> only. An array of Hall effect sensors <NUM> is associated with the reference track <NUM> and is configured to determine a coarse absolute position of the device over the single-track Gray code segment and to output a reference signal to the processing unit <NUM> indicative of the coarse absolute position of the device over the single-track Gray code segment of the reference track <NUM>. The distance between adjacent sensors <NUM> can be equal, but can be longer than a pole length of one or more poles on the reference track <NUM>. The single-track Gray code of the reference track <NUM>, when combined with the array of six Hall effect sensors <NUM>, can provide forty-eight coarse positions. However, forty-eight positions are not enough to provide the fine absolute position because the high resolution track includes one hundred twenty-eight pole pairs.

In order to increase the resolution for the one hundred twenty-eight pole pairs of the high resolution track <NUM>, a third track or second reference track <NUM> is provided. As illustrated in <FIG>, the third track <NUM> is located concentrically between the high resolution track <NUM> and the reference track <NUM>, and includes thirty-two North/South pole pairs, with each pole of each North/South pole pair being the same size (e.g., arc length). The arc length of each pole pair of the third track <NUM> encompasses four pole pairs of the high resolution track <NUM>. In this manner, the forty-eight course positions identifiable by the reference track <NUM>, in combination with the output from the third track <NUM>, can identify the fine absolute position over 4x32 = <NUM> pole pairs of the high resolution track <NUM>. For this higher resolution system <NUM>, another sensing ASIC <NUM>, such as a Timken MPS160 or MPS512 chip, is associated with the third track <NUM> and is used in place of an array of Hall effect sensors. The increased resolution/sensitivity of the chip <NUM> enables the use of more pole pairs on the third track <NUM> to increase the overall resolution of the encoder. Both the chip <NUM> and the array of Hall effect sensors <NUM> communicate with the processing unit <NUM>. In other embodiments, the chip <NUM> associated with the third track <NUM> and the processing unit <NUM> associated with the high resolution track <NUM> can be integrated into a single integrated circuit chip. It should be noted that the respective positions of the tracks (i.e., inside or outside of one another) can be varied from the illustrated embodiment.

<FIG> illustrates a third absolute position sensing system <NUM> that provides a resolution like the first system <NUM> in a different manner. The third sensing system <NUM> includes a first multi-polar magnetic ring or high resolution track <NUM>, which includes sixty-four magnetic pole pairs or North/South pole pairs. Each pole of each North/South pole pair is the same size (e.g., arc length). A second multi-polar magnetic ring or a reference track <NUM> is positioned concentrically within the high resolution track <NUM>. In the embodiment shown, the reference track <NUM> includes magnetic pole pairs or North/South pole pairs arranged to define a plurality of single-track Gray code segments or sections. As shown in <FIG>, there are four single-track Gray code segments 140a, 140b, 140c, and 140d on the reference track <NUM>. Each Gray code segment 140a, 140b, 140c, and 140d spans a ninety degree segment of the reference track <NUM>. In other embodiments, there could be two, three, five, or more Gray code segments making up the reference track <NUM>.

A sensor and processing unit <NUM> is associated with the high resolution track <NUM> and is configured to determine a position of the device over one of the North/South pole pairs of the high resolution track <NUM>. The processing unit <NUM> takes the form of a sensing ASIC, such as a Timken MPS160 or MPS512 chip, and is capable of determining the absolute position of a target magnet within one North/South pole pair of the high resolution track <NUM> only. An array of Hall effect sensors <NUM> is associated with the reference track <NUM> and is configured to determine a coarse absolute position of the device over any one of the single-track Gray code segments 140a, 140b, 140c, and 140d, and to output a reference signal to the processing unit <NUM> indicative of the coarse absolute position of the device over the respective single-track Gray code segment 140a, 140b, 140c, and 140d of the reference track <NUM>. Each of the single-track Gray code segments 140a, 140b, 140c, and 140d of the reference track <NUM>, when combined with the array of five Hall effect sensors <NUM>, can provide thirty coarse positions over each ninety degree arc length. The distance between adjacent sensors <NUM> can be equal, but can be longer than a pole length of one or more poles on a respective single-track Gray code segment 140a, 140b, 140c, and 140d of the reference track <NUM>.

In order to link the coarse positions of the four Gray code segments 140a, 140b, 140c, and 140d to the high resolution track <NUM>, a third track or second reference track <NUM> is provided. As illustrated in <FIG>, the third track <NUM> is located concentrically inside both of the high resolution track <NUM> and the reference track <NUM>, and includes a single North/South pole pair, with each pole of the single North/South pole pair being the same or slightly different size (e.g., arc length). An array of Hall effect sensors <NUM> (three sensors are shown) is associated with the third track <NUM> and communicates with the processing unit <NUM>. The output from the third track <NUM> can be used to determine the position within one of the four Gray code segments 140a, 140b, 140c, and 140d. In this manner, the thirty course positions identifiable by the each Gray code segment 140a, 140b, 140c, and 140d of the reference track <NUM>, in combination with the output from the third track <NUM>, can identify the fine absolute position within the sixty-four pole pairs of the high resolution track <NUM>. It should be noted that the respective positions of the tracks (i.e., inside or outside of one another) can be varied from the illustrated embodiment.

The third system <NUM> of <FIG> can provide the same resolution as the first system <NUM> however the third system <NUM> provides some advantages in terms of space and cost reduction. Specifically, as indicated by the arc length indicator <NUM>, all of the Hall effect sensors <NUM> and <NUM>, in addition to the chip of the processing unit <NUM> are confined within less than a one hundred and eighty degree span, and as illustrated, about a one hundred twenty-five degree span of the encoder. This means that if all of the sensors <NUM>, <NUM> and the chip <NUM> are combined onto a single chip, the chip size can be significantly reduced in comparison to a single chip supporting all of the sensors of the first system <NUM>. This opens up space over at least half of the encoder for additional hardware components. In fact, while not shown, in yet another embodiment, it is actually possible to achieve a further size reduction because the sensors <NUM> could even be moved closer together and centered on the top dead center position such that the arc length of the five sensors <NUM> would be the limiting factor on the size of the chip. In that embodiment, the circuit board could be confined to within about a seventy-five degree span of the encoder.

One of skill in the art will understand that with any of the disclosed embodiments having three circular tracks, the relative positions of the tracks can be selected as desired such that any of the tracks can be the outside, inside, or middle track.

Just as described with the system <NUM> illustrated in <FIG>, each of the systems <NUM>, <NUM>, and <NUM> can utilize the up/down data counter <NUM> and signal processing flow outlined in <FIG>. In yet other embodiments of signal processing for each of the systems <NUM>, <NUM>, <NUM>, and <NUM>, an alternative signal processing flow shown in <FIG> can be utilized. As shown in <FIG>, hardware or software can be utilized to provide an adding function at block <NUM>. This can be used in applications when an offset is desired for the encoder. In this flow, the initial value <NUM> and the output from the up/down counter <NUM> are separately input into the adder <NUM>, which can apply the desired offset function and then output the resulting absolute position signal.

Claim 1:
A system (<NUM>; <NUM>; <NUM>) for determining an absolute position of a device, the system comprising:
a high resolution track (<NUM>; <NUM>; <NUM>) having a plurality of North/South pole pairs, each pole of each North/South pole pair being a same size;
a sensor and processing unit (<NUM>; <NUM>; <NUM>) associated with the high resolution track (<NUM>; <NUM>; <NUM>) and configured to determine a position of the device over one of the North/South pole pairs of the high resolution track (<NUM>; <NUM>; <NUM>);
a reference track (<NUM>; <NUM>; <NUM>) having a plurality of North/South pole pairs arranged to define a single-track Gray code segment;
an array of Hall effect sensors (<NUM>; <NUM>; <NUM>) associated with the reference track (<NUM>; <NUM>; <NUM>) and configured to determine a coarse absolute position of the device over the single-track Gray code segment and to output a reference signal to the sensor and processing unit (<NUM>; <NUM>; <NUM>) indicative of the coarse absolute position of the device over the single-track Gray code segment;
a third track (<NUM>; <NUM>; <NUM>) having at least one North/South pole pair; and
at least one sensor (<NUM>; <NUM>; <NUM>) associated with the third track (<NUM>; <NUM>; <NUM>) and operable to output a third track signal used to determine a location within the single-track Gray code segment;
wherein the sensor and processing unit (<NUM>; <NUM>; <NUM>) combines the third track signal, the reference signal, and the position of the device over one of the North/South pole pairs of the high resolution track (<NUM>; <NUM>; <NUM>) to determine an initial, fine absolute position of the device.