WO2001022038A1

WO2001022038A1 - High resolution optical encoder

Info

Publication number: WO2001022038A1
Application number: PCT/US2000/026017
Authority: WO
Inventors: William Henry Witting
Original assignee: Delphi Technologies, Inc.
Priority date: 1999-09-21
Filing date: 2000-09-21
Publication date: 2001-03-29

Abstract

A method and system for measuring kinematic properties of a steering shaft (102) is disclosed. A recordable medium (204) is applied about the outer circumference of the steering shaft (102). The recordable medium (204) is encoded with information that may be read by a device (106, 112).

Description

H- 199374

HIGH RESOLUTION OPTICAL ENCODER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/155,166, filed on September 21, 1999, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This application relates to a high resolution optical encoder for measuring the kinematic properties of an automotive steering shaft.

BACKGROUND OF THE INVENTION

It is known in the art to provide sensor systems to measure the kinematic properties of automotive steering shafts. Such properties are made available to steering control systems to aid, for example, in power steering assist.

It is desirable that such sensor systems provide high resolution, be non- contacting, thus reducing or eliminating wear, be simple to assemble and be easily and precisely aligned and calibrated.

SUMMARY OF THE INVENTION

A method and system for measuring kinematic properties of an automotive steering shaft is disclosed. The method comprises encoding the shaft; directing a signal at the shaft; and sensing the signal reflected from the shaft.

The system comprises a recordable medium applied to the shaft, a signal source for directing a signal at the shaft and a sensor for sensing the signal reflected from the shaft. A device for recording a pattern is disclosed. The device comprises a substrate and a recordable medium having a prescribed optical property. The recordable medium is applied to the substrate.

High resolution encoders can be produced by printing or etching an optical pattern on a disk or cylinder. The kinematic properties of a shaft to which the disk or cylinder is affixed can be determined by first directing an interrogation signal at the pattern as the pattern moves past the interrogation signal and then reading the signal reflected from the pattern with a sensor. This method has the limitation that the minimum resolution of the sensor is controlled by the ability to print or scribe a distinct repeating pattern on the disk or cylinder. To ensure an accurate assessment of the kinematic properties of the shaft, the encoding requires high information density. This requires an encoding scheme that makes the best possible use of the high, but limited, resolution of the laser beam and read head optics. Furthermore, the encoding scheme requires minimum inter-symbol interference. This requires making the minimum run length, i.e. the minimum number of consecutive zero bits or one bits, as large as possible. In addition, the encoding scheme should be self-clocking. To avoid a separate timing track, the pattern should be encoded so as to allow the clock signal to be regenerated from the pattern. This requires limiting the maximum run length of the pattern so that transitions in the pattern will regenerate the clock. Still further, the encoding scheme should possess low digital sum value, i.e., the number of one bits minus the number of zero bits; thus minimizing the low frequency and DC content of the pattern. The highest resolution encoders created by this method generate a discrete signal, as each mark of the pattern is read by the sensor. A straight forward encoding would be to simply encode the zero bits as land and the one bits as pits. However, this does not meet the goal of high information density. The encoding scheme may encode one bits as transitions from pit to land or land to pit; and zero bits as constant pit or constant land. To meet the goals of minimum intersymbol interference and self-clocking, it is not possible to encode arbitrary binary data. For example, the integer 0 expressed as thirty-two bits of zero would have too long of a run length to satisfy the goal of self-clocking. To accommodate these goals, each eight-bit byte of actual data is encoded as fourteen bits of channel data. There are many more combinations of fourteen bits (i.e., 16,384) than there are of eight bits (i.e., 256). To encode the eight-bit combinations, 256 combinations of fourteen bits are chosen that meet the goals. This encoding is referred to as Eight-to-Fourteen Modulation (EFM) coding. If fourteen channel bits were concatenated with another set of fourteen channel bits, once again the above goals may not be met. To avoid this possibility, three merging bits are included between each set of fourteen channel bits. These merging bits carry no information but are chosen to limit the run length, keep data signal DC content low, etc. Thus an eight bit byte of actual data is encoded into a total of seventeen channel bits: fourteen EFM bits and three merging bits. To achieve a reliable self-clocking system, periodic synchronization is necessary. Thus data is broken up into individual frames.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a first representation of a high resolution encoder for measuring kinematic properties of an automotive steering shaft;

Figure 2 is a first cross sectional view of the automotive steering shaft of Figure 1;

Figure 3 is a second cross sectional view of the automotive steering shaft of Figure 1;

Figure 4 is a third cross sectional view of the automotive steering shaft of Figure 1;

Figure 5 is a fourth cross sectional view of the automotive steering shaft of Figure 1;

Figure 6 is a three dimensional representation of a sleeve for a high resolution encoder for measuring kinematic properties of an automotive steering shaft; Figure 7 is a first cross sectional view of the sleeve for the high resolution encoder of Figure 6;

Figure 8 is a second cross sectional view of the sleeve for the high resolution encoder of Figure 6;

Figure 9 is a third cross sectional view of the sleeve for the high resolution encoder of Figure 6;

Figure 10 is a fourth cross sectional view of the sleeve for the high resolution encoder of Figure 6;

Figure 11 is a second representation of a high resolution encoder for measuring kinematic properties of an automotive steering shaft;

Figure 12 is a representation of the surface of a disk of the high resolution encoder of Figure 11;

Figure 13 is a first representation of a high resolution encoder for measuring the torque on an automotive steering shaft; and

Figure 14 is a second representation of a high resolution encoder for measuring the torque on an automotive steering shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The new sensor uses a laser to read the change in an optical property caused by spots on a surface. A short length of a shaft is polished, coated with an organic dye, and coated with a clear plastic. During assembly of the sensor, a laser is used to write a digital sequence to this region by creating spots in the organic dye layer. This digital sequence is read by a lower power laser installed within the shaft housing to determine the position of the shaft. A flexible band consisting of a thin reflective material, or material possessing a prescribed optical property, coated with an organic dye and with a clear plastic layer may be wrapped around and fixed to the shaft to provide the sensing surface.

Referring now to Figure 1, a first embodiment of a high resolution encoder is shown generally at 100. The high resolution encoder 100 comprises a recordable medium 204 applied to a steering shaft 102, a signal source 106 for directing an interrogation signal 108 (at visible or non-visible wavelengths) at the steering shaft 102 and a sensor 112 for sensing the signal 110 reflected from the steering shaft 102. The steering shaft 102 is capable of translation and rotation. A pattern 122 is recorded in the recordable medium 204 thereby encoding the steering shaft 102. The pattern 122 may be a binary pattern comprising an array over which an optical property of the recordable medium 204 is alternately varied between two contrasting values. The method by which the pattern 122 is recorded in the recordable medium 204 depends upon the nature of the material of the recordable medium 204. The recordable medium 204 may be, for example, an organic dye or a phase change material or a magnetic material. In an organic dye, having a prescribed optical property such as reflectivity, or absorption, the pattern 122 may be recorded therein by the partial or complete ablation of a layer of the organic dye at prescribed location in the array. By partial ablation, only a portion of the layer of organic dye is removed at the prescribed locations. Thus, over the extent of the organic dye, the pattern 122 comprises a series of alternating pits 204a and lands 204b (Fig. 2). The pits 204a are depressions in the organic dye created by the partial ablation thereof and the lands 204b are the original surface of the organic dye such that the lands 204b retain the aforesaid optical property while the pits 204a alter the optical property. For instance, as seen in Figure 2, if the optical property of the organic dye is reflectivity, then an interrogation signal 108 striking a land 204b would be reflected therefrom 110a, while an interrogation signal 108 striking a pit 204a would be absorbed thereby or scattered therefrom. Conversely in Figure 2, it will be appreciated that if the optical property is absorption, then an interrogation signal 108 striking a land 204b would be absorbed thereby or scattered therefrom, while an interrogation signal 108 striking a pit 204a may be reflected therefrom 110b. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

By complete ablation, the entirety of the depth of the layer of the organic dye is removed, thus creating a pattern 122 comprising a series of alternating lands 204b and holes 204c (Fig. 3). The lands 204b retain the aforesaid optical property while the holes 204c alter the optical property. For instance, as seen in Figure 3, if the optical property of the organic dye is reflectivity, then an interrogation signal 108 striking a land 204b would be reflected therefrom 110c, while an interrogation signal 108 striking a hole 204c would pass through the hole to the unconditioned surface of the steering shaft 102 and may be absorbed thereby or scattered therefrom. Conversely, it will be appreciated that if the optical property of the organic dye is absorption, then the interrogation signal 108 striking a land 204b would be absorbed thereby, while an interrogation signal 108 striking a hole 204c would pass through the hole to the surface of the steering shaft 102 and may be reflected from a conditioned surface thereof 1 lOd. Such conditioning of the steering shaft 102 may comprise for example, polishing of the surface thereof or applying a reflective coating thereto. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

Thus, whether by partial or complete ablation, such ablation, over the surface of the recordable medium 204, alters or modifies a prescribed optical property of the recordable medium 204, thus producing a binary pattern 122 comprising some combination of a series of pits 204a or lands 204b or holes 204c representative of logic one or logic zero. The binary pattern 122 may then be addressed by the interrogation signal 108 and a signal 110a, 110b, 110c, 1 lOd reflected from the pattern 122 read or sensed by the sensor 112 and the kinematic properties of the steering shaft 102 determined thereby. In a phase change material having a prescribed optical property such as reflectivity, or absorption, the pattern 122 may be recorded therein by thermally forming regions of varying structural phase. For instance, as seen in Figure 4, in a crystalline material, the pattern 122 may comprise regions of amorphous structure 204d or polycrystalline structure 204e. The amorphous structure 204d and polycrystalline structure 204e possess differences in the prescribed optical property. For example, the polycrystalline structure 204e is more reflective than the amorphous structure 204d. Thus a binary pattern 122 is formed in the recordable medium 204 due to variations in the aforesaid optical property whereby an interrogation signal 108 striking a polycrystalline structure 204e would be reflected therefrom 1 lOe and an interrogation signal 108 striking a amorphous structure 204d would be absorbed thereby. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

In a magnetic material, the pattern 122 may be recorded therein by exploiting the magneto-optic effect wherein regions of varying magnetic polarity are created in the magnetic material. For instance, as seen in Figure 5, such polarity is either "up" 204f or "down" 204g, thereby creating a binary pattern in the recordable medium 204 which can be sensed or read by utilizing a polarization-sensitive sensor 112 such that an interrogation signal 108 striking an area of "up" polarization 204f would read a binary one 11 Of and an interrogation signal 108 striking an area of "down" polarization 204g would read a binary zero 1 lOg. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

Thus by encoding the steering shaft 102 with a pattern 122 the kinematic properties of the steering shaft 102 may be determined by directing an intenogation signal 108 at the steering shaft 102 and sensing the signal 1 lOe, 1 lOf, 1 lOg reflected from the pattern 122. In particular, the signal source 106 is operative for directing the interrogation signal 108 at the pattern 122. The sensor 112 is operative for sensing the signal 110 reflected from the steering shaft 102, and in particular from the pattern 122. The sensor 112 thence directs a signal 114 to a signal processing Unit 116 for determination of the kinematic properties of the steering shaft 102.

In Figure 6 a three dimensional representation of a sleeve 200 for a high resolution encoder is depicted. The sleeve 200 comprises a recordable medium 204 applied to a substrate 202. A pattern 122 is recorded in the recordable medium 204 and the sleeve 200 is placed on the steering shaft 102 of Figure 1, thus encoding the steering shaft 102 and allowing the kinematic properties thereof to be determined by directing an intenogation signal 108 at the steering shaft 102 and sensing the signal 110 reflected from the pattern 122.

As set forth hereinabove, the method by which the pattern 122 is recorded in the recordable medium 204 of the sleeve 200 depends upon the nature of the material of the recordable medium 204. The recordable medium 204 may be, for example, an organic dye or a phase change material or a magnetic material. In an organic dye, having a prescribed optical property such as reflectivity, or absorption, the pattern 122 may be recorded therein by the partial or complete ablation of a layer of the organic dye at prescribed locations in the array. As set forth above, by partial ablation, only a portion of the layer of the organic dye is removed at the prescribed locations. Thus, over the extent of the organic dye, the pattern 122 comprises a series of alternating pits 204a and lands 204b . The pits 204a are depressions in the organic dye created by the partial ablation thereof and the lands 204b are the original surface of the dye such that the lands 204b retain the aforesaid optical property while the pits 204a alter the optical property. For instance, as seen in Figure 7, if the optical property of the organic dye is reflectivity, then an interrogation signal 108 striking a land 204b would be reflected therefrom 1 lOh, while an intenogation signal 108 striking a pit 204a would be absorbed thereby or scattered therefrom. Conversely in Figure 7, it will be appreciated that if the optical property is absorption, then the interrogation signal 108 striking a land 204b would be absorbed thereby or scattered therefrom, while an intenogation signal 108 striking a pit 204a may be reflected therefrom 110k. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

As set forth above, by complete ablation the entirety of the depth of the layer of organic dye is removed, thus creating a pattern 122 comprising a series of alternating lands 204b and holes 204c. The lands 204b retain the aforesaid optical property while the holes 204c alter the optical property. For instance, as seen in Figure 8, if the optical property of the organic dye is reflectivity, then an intenogation signal 108 striking a land 204b would be reflected therefrom 110/, while an intenogation signal 108 striking a hole 204c would pass through the hole to the unconditioned surface of the substrate 202 and may be absorbed thereby or scattered therefrom. Conversely, it will be appreciated that if the optical property of the organic dye is absorption, then the intenogation signal 108 striking a land 204b would be absorbed thereby, while an intenogation signal 108 striking a hole 204c would pass through the hole to the substrate 202 and may be reflected from a conditioned surface thereof 110m. Such conditioning of the substrate 202 may comprise for example, polishing of the surface thereof or applying a reflective coating thereto. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

Thus, whether by partial or complete ablation, such ablation, over the surface of the recordable medium 204, alters or modifies a prescribed optical property of the recordable medium 204, thus producing a binary pattern 122 comprising some combination of a series of pits 204a or lands 204b or holes 204c representative of logic one or logic zero. The binary pattern 122 may then be addressed by the intenogation signal 108 and a signal 1 lOh, 110k, 110/, 110m reflected from the pattern 122 read or sensed by the sensor 112 and the kinematic properties of the steering shaft 102 determined thereby.

As set forth above, in a phase change material having a prescribed optical property such as reflectivity, or absorption, the pattern 122 may be recorded therein by thermally forming regions of varying structural phase. For instance, as seen in Figure 9, in a crystalline material, the pattern 122 may comprise regions of amorphous structure 204d or polycrystalline structure 204e. The amorphous structure 204d and polycrystalline structure 204e possess differences in the prescribed optical property. For example, the polycrystalline structure 204e is more reflective than the amorphous structure 204d. Thus a binary pattern 122 is formed in the recordable medium 204 due to variations in the aforesaid optical property whereby an interrogation signal 108 striking an area of polycrystalline structures 204e would be reflected therefrom 1 lOn and an intenogation signal 108 striking an area of amorphous structure 204d would be absorbed thereby. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

In a magnetic material, the pattern 122 may be recorded therein by exploiting the magneto-optic effect wherein regions of varying magnetic polarity are created in the magnetic material. For instance, as seen in Figure 10, such polarity is either "up" 204f or "down" 204g, thereby creating a binary pattern in the recordable medium 204 which can be sensed or read by utilizing a polarization-sensitive sensor 112 such that an intenogation signal 108 striking an area of "up" polarization 204f would read a binary one 1 lOp and an intenogation signal 108 striking an area of "down" polarization 204g would read a binary zero 11 Oq. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

Thus by encoding the sleeve 200 with a pattern 122 the kinematic properties of the steering shaft 102 may be determined by directing an interrogation signal 108 at the steering shaft 102 and sensing the signal reflected 1 lOp, 1 lOq from the pattern 122. In particular, the signal source 106 is operative for directing the intenogation signal 108 at the pattern 122. The sensor 112 is operative for sensing the signal reflected from the pattern 122 steering shaft 102, and in particular from the pattern 122. The sensor 112 thence directs a signal 114 to a signal processing unit 116 for determination of the kinematic properties of the steering shaft 102. Referring to Figure 11, a third embodiment of the high resolution optical encoder is shown generally at 300. The high resolution encoder 100 comprises a disk 120 (Fig. 12) secured to the steering shaft 102, the signal source 106 for directing an intenogation signal 108 at the disk 120 and the sensor 112 for sensing the signal reflected from the disk 120.

In Fig. 11 the recordable medium 204 is applied to the disk 120. The pattern 122 is recorded in the recordable medium 204, thus encoding the steering shaft 102 and allowing the kinematic properties of the steering shaft 102 to be determined by directing the interrogation signal 108 at the disk 120 and sensing the signal 110 reflected from the pattern 122. As set forth hereinabove, the method by which the pattern 122 is recorded in the recordable medium 204 depends upon the nature of the material of the recordable medium 204. The recordable medium 204 may be, for example, an organic dye or a phase change material or a magnetic material. In an organic dye, having a prescribed optical property such as reflectivity, or absorption reflectivity, or absorption the pattern 122 may be recorded therein by the partial or complete ablation of a layer of the organic dye at prescribed locations in the anay. As set forth above, by partial ablation, only a portion of the layer of the organic dye is removed at the prescribed locations. Thus, over the extent of the organic dye the pattern 122 comprises the series of alternating pits 204a and lands 204b. The pits 204a are depressions in the organic dye created by the partial ablation thereof and the lands 204b are the original surface of the organic dye such that the lands 204b retain the aforesaid optical property while the pits 204a alter the optical property. For instance, similar to that seen in Figures 2 and 7, if the optical property of the organic dye is reflectivity, then an interrogation signal 108 striking a land 204b would be reflected therefrom, while an interrogation signal 108 striking a pit 204a would be absorbed thereby or scattered therefrom. Conversely, similar to that seen in Figures 2 and 7, it will be appreciated that if the optical property is absorption, then the intenogation signal 108 striking a land 204b would be absorbed thereby while an intenogation signal 108 striking a pit 204a may be reflected therefrom. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

As set forth above, by complete ablation the entirety of the depth of the layer of the organic dye is removed, thus creating a pattern 122 comprising a series of alternating lands 204b and holes 204c. The lands 204b retain the aforesaid optical property while the holes 204c alter the optical property. For instance, as seen in Figure 3, if the optical property of the organic dye is reflectivity, then an intenogation signal 108 striking a land 204b would be reflected therefrom, while an intenogation signal 108 striking a hole 204c would pass through the hole to the unconditioned surface of the disk 120 and may be absorbed thereby or scattered therefrom.

Conversely, in Figure 3, it will be appreciated that if the optical property of the dye is absorption, then the interrogation signal 108 striking a land 204b would be absorbed thereby, while an intenogation signal 108 striking a hole 204c would pass through the hole to the disk 120 and may be reflected from a conditioned surface thereof. Such conditioning of the disk 120 may comprise for example, polishing of the surface thereof or applying a reflective coating thereto. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

Thus, whether by partial or complete ablation, such ablation, over the surface of the recordable medium 204 of the disk 120, alters or modifies a prescribed optical property of the recordable medium 204, thus producing a binary pattern 122 comprising some combination of a series of pits 204a or lands 204b or holes 204c representative of logic one or logic zero. The binary pattern 122 may then be addressed by the intenogation signal 108 and a signal reflected from the pattern 122 read or sensed by the sensor 112 and the kinematic properties of the steering shaft 102 determined thereby.

In a phase change material having a prescribed optical property such as reflectivity, or absorption the pattern 122 may be recorded therein by thermally forming regions of varying structural phase. For instance, similar to that seen in Figures 4 and 9, in a crystalline material, the pattern 122 may comprise regions of amorphous structure 204d or polycrystalline structure 204e. The amorphous structure 204d and polycrystalline structure 204e possess differences in the prescribed optical property. For example, the polycrystalline structure 204e is more reflective than the amorphous structure 204d. Thus a binary pattern 122 is formed in the recordable medium 204 due to variations in the aforesaid optical property whereby an intenogation signal 108 striking an area of polycrystalline structure 204e would be reflected therefrom and an intenogation signal 108 striking an area of amorphous structure 204d would be absorbed thereby. A protective layer 206 may be placed over the recordable medium 204 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

In a magnetic material, the pattern 122 may be recorded therein by exploiting the magneto-optic effect wherein regions of varying magnetic polarity are created in the magnetic material. For instance, as seen in Figures 5 and 10, such polarity is either "up" 204f or "down" 204g thereby creating a binary pattern in the recordable medium 204 which can be sensed or read_% by utilizing a polarization- sensitive sensor 112 such that an intenogation signal 108 striking an area of "up" polarization 204f would read binary one and an intenogation signal 108 striking an area of "down" polarization 204g would read binary zero. A protective layer 206 may be placed over the recordable medium 204 of the disk 120 to protect the recordable medium 204 from dust, dirt and to aid in maintaining long-term optical stability of the recordable medium 204.

By encoding the disk 120 with a pattern 122, the kinematic properties of the steering shaft 102 may be determined by directing an intenogation signal 108 at the steering shaft 102 and sensing the signal reflected from the steering shaft 102. In particular, the signal source 106 is operative for directing the intenogation signal 108 at the pattern 122. The sensor 112 is operative for sensing the signal reflected from the steering shaft 102, and in particular from the pattern 122. The sensor 112 thence directs a signal 114 to a signal processing unit 116 for determination of the kinematic properties of the steering shaft 102. With reference to Figures 13 and 14, the high resolution encoder 100 may be adapted to measure the relative rotation or relative translation of an upper and lower steering shaft 102a, 102b coupled by a torsion bar 124. By measuring the relative rotation of the upper and lower steering shaft 102a, 102b, it is possible to determine the net torque acting upon the torsion bar 124. By measuring the relative translation of the upper and lower steering shaft 102a, 102b it is possible to determine the compression or tension acting upon the torsion bar 124.

Information may be written into the recordable medium prior to assembly of the optical encoder. This is simple and inexpensive, but alignment problems may develop. The writing of the pattern into the recordable medium may also be accomplished after assembly of the system, thus allowing precise calibration of the sensor with respect to the pattern and accommodating any misalignment or other enors. This requires that a device for writing (e.g., high energy laser and associated circuitry) be included into the assembly. A rewritable recordable medium (e.g., amorphous polycrystalline material) may be utilized along with a writing device so that precise calibration of the optical encoder can be reestablished should the assembly fall out of alignment.

The proposed system and method for measuring the kinematic properties of an automotive steering shaft provide extremely high resolution which can be tailored to the particular application. The optically encoded disk is completely passive and non-contacting. The read sensor can be displaced from the encoded surface, thus eliminating wear and reducing alignment problems. Data may be encoded on the disk to provide direct, absolute measurement of position and direction of movement of the shaft. Multiple coordinated co-axial deflections can be read from the same sensor by using multiple read sensors, each with its own encoded track.

Writing of the pattern after assembly of the system allows for the precise calibration of the sensor with respect to the system. Writing the pattern before assembly allows for a less complex assembly process. In addition, no analog-to-digital conversion is required to use the sensor in a computer control system since the data is read and maintained digitally. While prefened embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration only, and such illustrations and embodiments as have been disclosed are not to be construed as limiting the claims.

Claims

CLAIMSWhat is claimed is:

1. A method of measuring kinematic properties of an automotive steering shaft comprising:

encoding the shaft;

directing a signal at the shaft; and

sensing the signal reflected from the shaft.

2. The method as set forth in Claim 1 wherein encoding the shaft includes encoding the surface of the shaft.

3. The method as set forth in Claim 1 wherein encoding the shaft includes encoding the shaft with a pattern.

4. The method as set forth in Claim 3 wherein directing a signal at the shaft includes directing a signal at the pattern.

5. The method as set forth in Claim 3 wherein sensing the signal reflected from the shaft includes sensing a signal reflected from the pattern.

6. The method as set forth in Claim 3 wherein encoding the shaft with a pattern includes:

applying a recordable medium to the shaft; and

recording a pattern in the recordable medium.

7. The method of claim 6 wherein said recordable medium is a rewritable recordable medium.

8. The method as set forth in Claim 6 further comprising conditioning a segment of the shaft.

9. The method as set forth in Claim 8 further comprising applying the recordable medium to the conditioned segment of the shaft.

10. The method as set forth in Claim 6 wherein recording a pattern in the recordable medium comprises recording a pattern having a varying optical property into the recordable medium.

11. The method as set forth in Claim 10 wherein recording a pattern having a varying optical property into the recordable medium includes recording a pattern thereinto having a varying optical property taken from the group of optical properties consisting of reflectivity, transmittance, and absorption.

12. The method as set forth in Claim 10 wherein recording a pattern having a varying optical property into the recordable medium includes recording a binary pattern thereinto.

13. The method as set forth in Claim 6 wherein applying a recordable medium to the shaft includes applying a recordable medium chosen from the group consisting of organic dyes, phase change materials and magnetic materials.

14. The method of as set forth in Claim 1 wherein encoding the shaft includes

applying a sleeve thereto, the sleeve having

a substrate; and

a recordable medium having a prescribed optical property; the recordable medium applied to the substrate.

15. The method as set forth in Claim 14 wherein directing a signal at the shaft includes directing a signal at the sleeve.

16. The method as set forth in Claim 14 wherein sensing the signal reflected from the shaft includes sensing a signal reflected from the sleeve.

17. The method as set forth in Claim 1 wherein encoding the shaft includes securing a disk to the shaft.

18. The method as set forth in Claim 17 wherein securing a disk to the shaft includes:

applying a recordable medium to the disk; and

recording a pattern into the recordable medium.

19. The method as set forth in Claim 18 wherein recording the pattern into the recordable medium comprises recording a pattern having a varying optical property into the recordable medium.

20. The method as set forth in Claim 19 wherein recording a pattern having a varying optical property into the recordable medium includes recording a pattern thereinto having a varying optical property taken from the group of optical properties consisting of reflectivity, transmittance and absorption.

21. A system for measuring kinematic properties of an automotive steering shaft comprising:

a recordable medium applied to the shaft;

a signal source for directing a signal at the shaft; and

a sensor for sensing the signal reflected from the shaft.

22. The system as set forth in Claim 21 wherein the recordable medium is taken from the group of recordable media consisting of organic dyes, phase change materials and magnetic materials.

23. The system as set forth in Claim 22 wherein the recordable medium comprises a recordable medium having a prescribed optical property.

24. The system as set forth in Claim 23 wherein the recordable medium includes a pattern recorded therein.

25 The system as set forth in Claim 24 wherein the pattern comprises a pattern having a varying optical property.

26. The system as set forth in Claim 21 wherein the shaft includes a polished segment thereof.

27. The system as set forth in Claim 21 wherein the signal source comprises an optical signal source.

28. The system as set forth in Claim 27 wherein the optical signal source includes a laser.

29. The system as set forth in Claim 21 wherein the sensor comprises a light sensing diode.

30. The system as set forth in Claim 21 further including a controller for accepting as input thereto a signal indicative of the signal reflected from the pattern.

31. A device for recording a pattern, the device comprising:

a substrate; and

32. The device as set forth in Claim 31 wherein the recordable medium is taken from the group consisting of organic dyes, phase change materials and magnetic materials.

33. The device as set forth in Claim 31 wherein the prescribed optical property is taken from the group of optical properties consisting of reflectivity, transmittance and absorption.

34. The device as set forth in Claim 31 wherein the prescribed optical property is taken from the group of optical properties consisting of reflectivity, transmittance and absorption.

35. The device as set forth in Claim 21 wherein said recordable medium is a rewritable recordable medium.