WO1997021069A1

WO1997021069A1 - Generating data about the surface of an object

Info

Publication number: WO1997021069A1
Application number: PCT/US1996/019448
Authority: WO
Inventors: Saul Kato
Original assignee: Sven Technologies, Inc.
Priority date: 1995-12-05
Filing date: 1996-12-05
Publication date: 1997-06-12
Also published as: AU1282097A; EP0811145A4; EP0811145A1; CA2212355A1; KR19980702065A; JPH11502027A

Abstract

A sensing system which includes a surface sensing device (20) is provided for generating a representation of an object (22) using an array of sensing elements (23) that may have a sensing pin and a cylindrical housing. The sensing elements (23) generate a signal representing a height of various points on the surface of the object (22) relative to a reference plane. The sensing elements (23) may be resistive sensing elements or capacitive sensing elements.

Description

GENERATING DATA ABOUTTHE SURFACEOFAN OBJECT

Background of the Invention

The invention relates generally to generating representations of a three- dimensional object on a computer screen, and more particularly to surface sensing devices that quickly and efficiently generate data representing the contour of the surface of a three-dimensional object.

Systems and methods for generating two-dimensional information about an object are well known. These well known two-dimensional systems

typically use a flat table that has a touch sensitive surface. To generate data for a particular point, a stylus is used to depress the touch-sensitive surface and cause electrical signals to be generated relating to the position of the stylus on the table. These stylus position signals may be used to generate two-dimensional data about the object. These two-dimensional digitizing systems, however, are not suitable for generating data about the surface of three-dimensional objects.

Systems and methods for generating three-dimensional data about an object and for displaying a representation of the object on a computer screen are also well known for such applications as computer aided drafting and machining (CAD/CAM), medical analysis and visualization, and modeling of objects. These well known three-dimensional data generation devices may

SUBSTTTUTE SHEET (RULE 26) include either a mechanical probe coordinate measuring machine (CMM), or an optical system. The CMM systems generally use a type of electromechanical probe to contact and follow the surface of the object and generate data relating to the surface of the object along the scan line. The data generation process is repeated for successive scan lines until data is gathered for the entire object. Then, the data is combined to form a three-dimensional representation of the object. The systems for combining scan-line data into a representation of the object are well known. These mechanical probe systems are slow because the mechanical probe has to be moved over the entire surface of the three-dimensional object in order to generate the data. In addition, these mechanical probe systems require expensive, complex, large machines, and require a large amount of processing power to control the mechanical probe and process the scan-line data. In addition, only a person that is specifically trained can operate the system.

The known optical systems typically use incandescent light or laser light to generate data relating to the surface of the object. In one optical system, light is projected towards the object and the reflected light from the surface of the object is received by a sensor. In another optical system, a video camera is used to form images of an object at various different angles to generate data about the surface of the object. These optical systems can generate data concurrently for a large portion of the object so that the time necessary to generate data for the entire object is reduced. These optical

systems, however, are susceptible to misalignment problems that can corrupt the generated data. In addition, these optical systems are expensive, large machines that must be operated by a trained person.

All of these known three-dimensional sensing systems are generally large, expensive, immovable machines. In addition, known types of three- dimensional sensing systems tend to be complex machines that require a large amount of data processing. In addition, these known sensing systems are difficult for the average person to use because they are so complex, and the systems can not readily be attached to a personal computer. There is a need for sensing systems and methods which are relatively simple, inexpensive, and fast for sensing the surface contour of a three-dimensional object to enable a representation of the object to be generated.

Thus, there is a need for surface sensing systems and methods which avoid these and other problems of known devices, and it is to these ends that

the present invention is directed.

Summary of the Invention

The invention provides a surface sensing system which is inexpensive, portable, and can quickly generate three-dimensional data about the surface of an object. The surface sensing system of the invention may be easily moved and may also be quickly calibrated. In addition, the surface sensing system is a device that may be easily interfaced to a personal computer and may be operated by an average person without any specific training.

A surface sensing system in accordance with the invention includes an array of sensing elements for contacting the surface of the object, and a system associated with each sensing element for providing a signal representing the location of a corresponding point on the surface of the object contacted by the sensing element relative to a reference plane. A processor generates a representation of the object from the signals generated by the sensing elements. Each sensing element may have a system for indicating a relative displacement of the sensing element with respect to the reference plane. The system may use either resistive sensing elements or reactive, e.g., capacitive, sensing elements. In addition, the array of sensing elements may be of any convenient size and may have a density of sensing elements per unit area that affords the desired degree of resolution of measurement. The individual sensing elements may also be of any convenient size.

The invention also provides a method for generating a representation of an object in which the surface of the object is contacted by an array of sensing elements, signals representing the locations of points on the surface of the object relative to reference plane are generated by the array of sensing elements, and the signals are processed to generate a representation of the object. Brief Description of the Drawings

Figure 1 is a block diagram depicting a surface sensing system in accordance with the invention;

Figure 2 is a perspective view of an embodiment of a surface sensing device in accordance with the invention that may employed with the surface sensing system shown in Figure 1;

Figure 3 is an enlarged cross-sectional view of a first embodiment of a sensing element of the sensing device of Figure 2;

Figure 4 is a front view of the back mounting plate of the sensing device shown in Figure 2;

Figure 5 is a front view of the front mounting plate of the sensing device shown in Figure 2;

Figure 6 is a enlarged cross-sectional view of another embodiment of a sensing element of the sensing device of Figure 2; Figure 7 is a side view showing the surface sensing device of the invention being used to generate data about a three-dimensional object;

Figure 8 is a top view showing the surface scanning device of the invention being used to generate data about the three-dimensional object of Figure 7; Figure 9 is a flowchart showing a method of sensing a three- dimensional object in accordance with the invention; and

Figure 10 is a flowchart showing a method of sensing one side of a three-dimensional object in accordance with the invention. Detailed Description of Preferred Embodiments

The invention is particularly applicable to a surface sensing system and method that provides an inexpensive, fast way of sensing a three-dimensional object, such as small hand-held objects, to produce data about the surface of the object, to permit generation of a representation of the object on a computer screen, and will be described in that context. It will be appreciated, however, that the system and method in accordance with the invention has greater utility.

Figure 1 is a block diagram depicting a sensing system in accordance with the invention. The sensing system may include a surface sensing device

20 that will be described in more detail below with reference to Figures 2-6. The surface sensing device 20 is generally used to generate data about the surface characteristics of a three-dimensional object 22. Generally, the surface sensing device generates signals that represent the contour of the surface of the object. This may be by signals that represent the locations, e.g., heights, of various points on the surface of the object relative to a reference plane. Once these signals are produced, they can be processed to generate representations

of the object that may be displayed on a computer screen. The data or the representations may also provide data to a computer aided design (CAD) package or any other system that can manipulate object data. The surface sensing device may have a plurality of sensing elements 23 arranged in an array or matrix supported by a mounting plate 21. However, the surface sensing device may be composed of any number of sensing elements in any desired configurations and may have any desired density of sensing elements per unit area. The matrix of sensing elements may be an X-Y matrix of sensing elements. These sensing elements will be described in more detail

below.

In this embodiment, an X multiplexer 24 and a Y multiplexer 26 may be used to sequentially sample each sensing element within the X-Y matrix in order to determine the signals from each individual sensing element in the array. Thus, the X multiplexer and the Y multiplexer allow the sensing system to scan each row and column of the array of sensing elements in order to generate signals for each individual point on the surface of the object contacted by the corresponding sensing element. The matrix of sensing elements may also be sampled by any other sampling system, such as multiple parallel inputs. The method of generating three-dimensional data using these multiplexers will be described in more detail below.

Each sensing element has a system associated with it for producing a signal representing the location of a point on the surface of the object contacted by the sensing element relative to a reference plane. In other words, each sensing element has a system that converts the signal from the sensing element into a signal that corresponds to the location of a point on the surface of the object relative to a reference plane. Once the signals representing the location of a point on the surface of the object relative to a reference plane are produced, the signal are then processed to generate a representation of the object. No complex calculations or systems for controlling the sensing device are required. Thus, data about the surface of the object may be generated quickly and inexpensively. The system for producing the signals representing the location of points of the surface of the object relative to a reference plane and the processing system will be described in more detail below.

The system for producing the signals representing the location of points of the surface of the object relative to a reference plane may include a sampling circuit 28. This sampling circuit may be a high frequency A/C capacitance bridge that generates an electrical signal corresponding to the capacitance of a capacitive sensing element, or a Wheatstone bridge that generates an electrical signal corresponding to the resistance of a resistive sensing element. The capacitive sensing element will be described below with reference to Figure 3, and the resistive sensing element will be described below with reference to Figure 6. The A/C capacitance bridge and the

Wheatstone bridge sample either the capacitance or resistance, respectively, of the sensing element and generate a corresponding electrical signal. Once all of the electrical signals are generated by the sampling circuit, the signals are converted into digital signals by an analog-to-digital (A/D) converter 30. After these signals are converted into a digital format, they are fed into a computer interface 32. The computer interface may be a microprocessor. The computer interface 32 controls the operation of the X multiplexer 24 and the Y multiplexer 26 in order to generate signals for each sensing element of the sensing device and also processes the signals from the signal producing system in order to generate a representation of the object that can be displayed on a computer display. The computer interface, in turn, may be connected to a computer 34 that has a display 36.

Figure 2 is a perspective view of the sensing device 20 shown in Figure

1. As shown, the sensing device may comprise a plurality of individual sensing elements arranged in an array or matrix. The sensing device may include a front mounting plate 50 and a back mounting plate 52. In addition, there are a plurality of sensing elements 23 that are connected between the front mounting plate and the back mounting plate. These sensing elements may be any type of sensing device that provides a signal representing the location of a point on the surface of an object relative to a reference plane. Preferred embodiments of these sensing elements will be described in more detail below with reference to Figures 3 and 6.

Each of the sensing elements may comprise a body portion 54 having a sensing pin 56 that is biased to extend outwardly from the end of the sensing element body. For clarity, only a small number of sensing elements and sensing pins are shown in Figure 2, but the sensing device may have, for example, a full X-Y matrix of sensing elements of any appropriate size and density. The sensing pins may be of any desirable length and depends on the size of the object. The plurality of the sensing elements may form an array of sensing elements. The number of sensing elements within the array per unit area and the spacing of the sensing elements within the array, e.g., the density of sensing elements, determine the resolution of the sensing device. For example, if the array has many closely spaced sensing elements, then the sensing device has a high resolution. On the other hand, an array with fewer sensing elements spaced farther apart from each other has a lower resolution.

The number and spacing of the sensing elements in the array may vary and be selected for the resolution required for a particular application. In fact, the sensing elements within the array may be detachable from the front and back mounting plates, if desired, so that the array may be customized easily. Each sensing element independently generates a signal representing the location of a point on the surface of the object relative to a reference plane. In other words, the sensing elements determine a contour of the surface of an object by measuring the location of a point on the surface of the object relative to any plane. The reference plane may be the back mounting plate so that the sensing elements measure the height of points on the surface of the object relative to the back mounting plate. If the reference plane is the back mounting plate, then the sensing device of the invention may be used to produce data about an object even if the sensing device is upside down. However, the reference plane may be any other plane, such as the surface upon which the object is resting.

Figure 3 is a cross-sectional side view of a first embodiment of a sensing element 23 that may be employed in the sensing device 20 shown in Figure 2. The sensing element shown in Figure 3 is a capacitive sensing element 55 that may be attached between the front mounting plate 50 and the back mounting plate 52 of the sensing device. The capacitive sensing element is a variable capacitance device, and may include a sensing pin 56 that is slideably disposed within a cylindrical housing 72, and biased outwardly from the housing by a spring 66. An interior end of the sensing pin may be attached to a stopper and sliding guide 64. The spring 66 may engage the guide 64 to bias the sensing pin outwardly through the front mounting plate.

In addition, an insulating pin guide 68 disposed in front plate 50 may guide the sensing pin, and a back plug 70 may attach the spring to the back mounting plate.

The sensing pin 56 and the cylindrical housing 72 that surrounds the sensing pin may both be metallic. The combination of the metallic sensing pin 56 and the cylindrical housing 72 form a capacitor whose capacitance varies with the location of the sensing pin in the cylindrical housing. In other words, the distance that the sensing pin is pushed back into the cylindrical housing may be determined by measuring the change in capacitance relative to a reference value. The capacitive sensing element may also include an outer shielded housing 74 that protects the capacitor from damage. An electrical brush contact 76 connects the sensing pin 56 to the front mounting plate 50. The cylindrical housing 72, which is the other part of the capacitor, is connected to the back mounting plate 52 by the back plug 70. Thus, the capacitance of the capacitive sensing element is measured by measuring the capacitance of the electrical circuit formed by the electrical brush contact, the sensing pin, the cylindrical housing, and the back plug. Figure 4 is a front view of the back mounting plate 52 of the sensing device shown in Figure 2. As shown, the back mounting plate may have a plurality of electrical traces 80 that vertically (in this figure) connect the back plug 70 and the cylindrical metallic housing (not shown) of various sensing elements of the sensing device to each other. One end of all of the electrical traces 80 are connected together to form a common lead 82. The other ends of the electrical traces are combined into a cable 84 as individual conductors that connect to the Y multiplexer (not shown).

Figure 5 is a front view of the front mounting plate 50 of the sensing device as shown in Figure 2. The front mounting plate may also have a plurality of electrical traces 90 that are connected to a horizontal (in this figure) row of electrical brush contacts 76 of various sensing elements. One end of these electrical traces are connected together to form a second common lead 92. The other end of the electrical traces are combined in a cable 94 as individual conductors that connect to the X multiplexer (not shown).

In operation, when the sensing device with a plurality of capacitive sensing elements is placed over an object to be sensed and the device is pushed down, each sensing pin is displaced into the cylindrical housing a certain amount depending on the height of the corresponding point on the

surface of the object which the pin contacts, and the spring is compressed.

When each sensing pin is pushed back, more of the sensing pin is in close proximity to the cylindrical housing and the capacitance of the sensing element increases. The electrical traces 80, 90 form an X-Y matrix of conductors. The capacitance of each individual sensing element may be measured by selecting a particular electrical trace on the back mounting plate using the Y multiplexer, and a particular electrical trace on the front mounting plate using the X multiplexer which intersect at the selected sensing element.

For example, with reference to Figures 3, 4 and 5, to measure the capacitance of a selected sensing element 96, an electrical trace 97 on the back mounting plate in combination with an electrical trace 98 on the front mounting plate are selected by the multiplexers. The capacitance is then measured by the sampling circuit as the capacitance of the electrical circuit formed by the electrical trace 97, the back plug 70, the cylindrical housing 72, the sensing pin

56, the electrical brush contact 76, and the electrical trace 98.

Figure 6 is a cross-sectional view of another embodiment of a sensing element 23 that may be employed in the sensing device 20 shown in Figure 2. The sensing element shown in Figure 6 is a resistive sensing element 100 that may have a sensing pin 102 slideably disposed within a guide housing 104 that may have a resistive strip 106 attached to it. The sensing pin is biased outwardly from the housing by a spring 109. The resistive sensing element is a variable resistance device. The sensing pin and guide housing may both be metallic. An interior end of the sensing pin may be attached to a stop plug

108, and the sensing pin is guided through the front mounting plate 50 by a front guide 110. A front electrical brush contact 112 electrically connects the sensing pin to an electrical trace (not shown) of the front mounting plate 50. A rear stopper 114 connects the guide housing 104 to the back mounting plate

52. A second electiical brush contact 116 electrically connects the sensing pin to the resistive strip. An electrical connector 118 connects the resistive strip to the electrical traces (not shown) on the back mounting plate 52. The electrical traces of the front and back mounting plates, described above with reference to Figures 4 and 5, may also be used in connection with this resistive sensing eleme

In operation, as each resistive sensing pin is displaced into the guide housing a certain amount depending on the height of the corresponding point on the surface of the object which the sensing pin contacts, the second electrical brush contact 116 slides backwards over the resistive strip 106 and the resistance of the resistive sensing element is reduced. The resistance of an individual resistive sensing element is determined by selecting the individual resistive sensing element using the multiplexers and by using the sampling circuit to measure the resistance of the electrical circuit formed by the electrical trace on the front mounting plate, the front electrical brush contact

112, the sensing pin 102, the second electrical brush contact 116, the resistive strip 106, the electrical connector 118, and the electrical trace on the back mounting plate. Thus, the resistive sensing element has a varying resistance that can be measured by the sampling circuit, such as a Wheatstone bridge, as described above, and converted into an electrical signal representing the

height of a particular point on the surface of the object above a reference

plane. Figure 7 is a side view of the surface sensing device of the invention being used to generate data about a three-dimensional object 130, such as a vase. The object 130 is three-dimensional, but only its side shape is shown for clarity. In order to generate data representing the entire object 130, data must be generated for two or more sides of the object by moving either the object or the sensing device. The surface sensing device 20 may be placed over the vase so that the front mounting plate 50 is near the highest surface of the vase.

In locations where the surface of the vase has some height, the sensing pins 56 of the sensing elements 54 are pushed back various distances depending on the height of the surface of the vase. The varying distances of the sensing pins correspond to varying capacitance or resistive values of the sensing element, as described above. At locations where the surface of the vase is not present, the sensing pins 56 are fully extended due to the spring and have a maximum resistance value or a minimum capacitance value, depending on the type of sensing element used. The length of the sensing pins may preferably be long enough so that the sensing pins, that do not touch the surface of the object, contact the surface that the object is resting on.

Figure 8 is a top view of the sensing device 20 of the invention being used to generate data about the object 130. The array of sensing elements 56, in this embodiment is a rectangular configuration, but any configuration, such as a circle or square may be used. The number of sensing elements within the array of sensing elements may be increased or decreased depending on the size of the object and the desired resolution. As described above, the array of sensing elements allows the sensing device to generate data for a large portion of an object quickly. If the object is larger that the sensing device, then extra sensing elements may be added. If the object is still too large with the addition of the extra sensing elements, then data about the surface of the entire object may be generated by repeatedly using the sensing device of the

invention and then processing the data to produce a representation of the object.

Figure 9 is a flowchart showing a method of sensing a three- dimensional object and generating a representation of the object in accordance with the invention. The method is started in Step 140. In Step 142, the heights of various points on a first side of an object are determined using the sensing device. Then in Step 144, the data for another side of the object is generated using the sensing device. In Step 146, it is determined whether or not data has been generated for all of the sides of the object. For example, the vase shown in Figures 7 and 8 may require two sides of the vase to be sensed using the scanning device in order to generate sufficient data. The details of sensing each side of an object are described below with reference to Figure 10. If additional sides of the object need to be sensed to generate sufficient data, then the method returns to Step 144, and data for another side of the object is generated. As the surface of a three-dimensional object becomes more complex, data for additional sides of the object may be required. On the other hand, if all sides of the object have been sensed and sufficient data has been generated, then in Step 148, the data from the various sides of the object are processed and combined together to generate a representation of the object.

The technique for combining the data for the various sides of the object to generate the representation of the object is well known. The method is then completed in Step 150. In this manner, a graphical representation of a three- dimensional object may be generated and displayed on a computer system.

Figure 10 is a flowchart showing a method of generating data for each side of a three-dimensional object in accordance with the invention. In Step 160, the method is begun. In Step 162, a first electrical trace on the front mounting plate is selected by the X multiplexer. This first electrical trace horizontally connects a number of sensing elements. In Step 164, a first electrical trace on the back mounting plate is selected by the Y multiplexer. The combination of the electrical trace of the front mounting plate and the electrical trace of the back mounting plate selects a single sensing element that is then sampled in accordance with the invention. In Step 166, the next sensing element in the row selected by the X multiplexer is sampled by incrementing the Y multiplexer. In Step 168, it is determined whether or not the row is complete (i.e., whether each sensing element in the row has been sampled). If the row has been completed, then the method returns to Step 166 in which the next column is selected by the Y multiplexer and the next sensing element is the row is sampled. If the row is complete, it is then determined in Step 170 whether or not the entire scan of the array has been completed. If the scan has not been completed, then the method returns to Step 162 in which the next row of sensing elements is selected by selecting the next electrical trace on the front mounting plate. On the other hand, if the scan is done then the method is completed in Step 172. In this manner, using the X and Y multiplexers, the entire array of sensing elements are scanned and signals are generated for each element. These signals are then processed and turned into electrical signals representing the height of the surface of the object above a reference plane.

The three-dimensional sensing device of the invention may also be quickly and easily calibrated by placing an object with a known surface contour, e.g., flat, underneath the sensing device. Then, the actual output of the sensing device may be compared to the anticipated output and the sensing device may be adjusted. This process of calibrating the sensing device may be conducted by the computer interface.

While the foregoing has been with reference to a particular embodiment of the invention, it will be appreciated by those skilled in the art that changes in this embodiment may be made without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims.

Claims

I Claim: 1. A system for generating a representation of an object, comprising an array of sensing elements for contacting the surface of the object; means associated with each sensing element for providing a signal representing the location of a corresponding point on the surface of the object contacted by the sensing element relative to a reference plane; and means for processing the signals from the array of sensing elements to generate a representation of the object.

2. The system of Claim 1, wherein the providing means for each sensing element comprises means for indicating a relative displacement of the sensing element away from the reference plane.

3. The system of Claim 2, wherein each sensing element in the array of sensing elements comprises a housing and a sensing pin slideable located within the housing, and the signal providing means is responsive to the location of the sensing pin with respect to a reference point of the housing.

4. The system of Claim 3 further comprising a front mounting plate that has a plurality of electrical traces extending in a first direction and connecting the sensing elements to each other, and a back mounting plate that has another plurality of electrical traces extending in a second direction and connecting the sensing elements to each other.

5. The system of Claim 3, wherein the indicating means includes means for detecting variance in the capacitance of the sensing element as the sensing element is displaced relative to the housing.

6. The system of Claim 5, wherein the detecting means comprises means for individually sampling each sensing element, and means for generating an electrical signal representing the capacitance of each sensing element.

7. The system of Claim 3, wherein the indicating means includes means for detecting variance in the resistance of the sensing element as the sensing element is displaced relative to the housing.

8. The system of Claim 7, wherein the detecting means comprises means for individually sampling each sensing element, and means for generating an electrical signal representing the resistance of each sensing element.

9. A method for generating a representation of an object, comprising contacting a surface of the object with an array of sensing elements; providing, from each of the sensing elements, a signal representing the location of a corresponding point on the surface of the object contacted by the sensing element relative to a reference plane; and processing the signals from the array of sensing elements to generate a representation of the object.

10. The method of Claim 9, wherein providing a signal for each sensing element comprises indicating a relative displacement of the sensing element away from the reference plane.

11. The method of Claim 10, wherein providing a signal for each sensing element comprises providing a signal that is responsive to the relative location of a sensing pin in each sensing element with respect to a reference point of a housing of the sensing element.

12. The method of Claim 9, wherein providing the signal comprises

sampling the array of sensing elements individually to detect variances in the capacitance for each sensing element as the sensing element is displaced relative to the reference plane.

13. The method of Claim 12, wherein the providing the signal comprises converting the capacitance signal into an electrical signal for each sensing element.

14. The method of Claim 9, wherein providing the signal comprises sampling the array of sensing elements individually to detect variances in the resistance for each sensing element as the sensing element is displaced relative to the reference plane.

15. The method of Claim 14, wherein the providing the signal comprises converting the resistance signal into an electrical signal for each sensing element.

16. A sensor for use by a processing system for generating a representation of an object, the sensor comprising an array of sensing elements for contacting the surface of the object; and means associated with each sensing element for providing a signal representing the location of a corresponding point on the surface of the object contacted by the sensing element relative to a reference plane.

17. The sensor of Claim 16, wherein the providing means for each sensing element comprises means for indicating a displacement of the sensing element relative to the reference plane.

18. The sensor of Claim 17, wherein each sensing element in the array of sensing elements comprises a housing and a sensing pin slideable located within the housing, and the signal providing means is responsive to

the relative location of the sensing pin with respect to a reference point of the housing.

19. The system of Claim 18 further comprising a front mounting

plate that has a plurality of electrical traces extending in a first direction and connecting the sensing elements to each other, and a back mounting plate that has another plurality of electrical traces extending in a second direction and connecting the sensing elements to each other.

20. The sensor of Claim 18, wherein the indicating means includes means for detecting variance in the capacitance of the sensing element as the sensing element is displaced relative to the housing.

21. The system of Claim 20, wherein the detecting means comprises means for individually sampling each sensing element, and means for generating an electrical signal representing the capacitance of each sensing element.

22. The system of Claim 18, wherein the indicating means includes means for detecting variance in the resistance of the sensing element as the sensing element is displaced relative to the housing.

23. The system of Claim 22, wherein the detecting means comprises means for individually sampling each sensing element, and means for generating an electrical signal representing the resistance of each sensing element.