The present invention was not made under federally sponsored research or development.
The invention relates to non-contact camera-based pointing devices with application in machining, on-machine inspection, and reverse engineering.
Aligning the axis of rotation or the axis of symmetry of a machine with a point on a target is needed, among others, for machining, on-machine inspection, and reverse engineering. One important application in machining is providing a reference point(s) on the surface of a workpiece for a CNC machine.
Camera-based pointing devices are well known and widely used. The usual and obvious way to build them is to concentrically align all components of a pointing device, such as the shank, the image sensor, the lens, and a cross-hair or other form of pointing insignia in the view. The pointing insignia can be added electronically as an overlay to the image from the camera. One example of the previous art in pointing devices can be found in U.S. Pat. No. 6,647,840 B2, Nov. 18, 2003. The common problem in all known solutions is the high cost of building a pointing device that is almost perfectly concentric. It becomes even more challenging if a variable focus lens is to be used because not just the lens itself must be concentric but also it has to be mounted and rotate concentrically. Maintaining concentricity for the life span of the tool and resistance to accidental shocks and vibrations are also a problem making the known camera-based pointing devices delicate and fragile instruments.
Contrary to the prior art it has been discovered by the Applicant that in order to build a perfectly concentric camera-based pointing device it is not necessary to make concentric all components of the pointing device itself. Instead, it is possible to rely on an axial symmetry created by rotation of the machine on which the pointing device is used or on an axial symmetry created by rotating the pointing device itself in a manner concentric with any axis of interest on the machine on which it is used. For the pointing device itself it is sufficient to have a highly concentric shank and a rigid design that will maintain all pointing device components at fixed locations in reference to the shank. Concentricity of the shank is required to achieve repeatable insertion into the machine or ability to precisely rotate the pointing device in reference to the machine. The image generated by the pointing device can be free from any pointing insignia. A freely user-adjustable on-screen pointer and a pointer alignment method will be needed to mark the location of the center of the rotation as observed on the screen. The pointer can be added as an overlay to the said image. One example of such a pointer can be the usual on-screen pointer used in computer systems based on Windows® by Microsoft Corporation or Macintosh® computers manufactured by Apple Computer Corporation. A readjustment of the on-screen pointer will be needed each time the geometry of the pointing device components changes, e.g., a change of focus. A fast converging method has been discovered that makes the pointer position adjustment possible. The method works in the presence of optical distortions and is highly tolerant of inexact 180 degree rotation that is required in the process of adjusting the pointer location. It is the combination of the highly concentric camera shank and the pointer adjustment method that makes a low cost extreme precision camera-based pointing device possible and constitutes the core of the present invention.
It was observed and consequently discovered, that in order to build a perfectly concentric camera-based pointing device, contrary to the previous art, there is no need to make any of the components of the camera, such as lens or image sensor coaxial with the rotational axis of the machine on which the pointing device is used. All that is needed is: (a) a highly concentric shank creating a concentric interface with the machine and (b) an on-screen pointer position adjustment method that would exhibit fast convergence to the on-screen image of the point at the intersection between the axis of rotation of the machine and the surface of a workpiece or a target. Ability of the pointing device to concentrically rotate along the axis of rotation, or the axis of symmetry, or any axis of interest on the machine on which the pointing device is used is assumed. This can be facilitated by a spindle or, in the simplest implementation, a calibrated bore.
The present invention yields pointing devices of potentially zero error, devices that can be manufactured at low cost, maintain concentricity for the lifetime of the tool, and do not rely on high quality optics or image sensors to deliver extreme concentricity.
The description of the invention shows how to make and use a pointing device capable of extreme concentricity. As result of close to perfect concentricity and known maximum errors the pointing device built and used per the present invention can be used to calibrate other types of pointing devices, such as but not limited to laser pointers.
a is a view showing a light beam forming an image of the point on the target that is aligned with the axis of rotation of a machine on which the pointing device is used. The image is projected on the surface of the image sensor.
b is a view similar to
a is a view showing the graphical display with the image of the point on the target with camera aligned to 0 degrees and when there is no alignment between the point on the target and the axis of rotation.
b is a view similar to
c is a view showing the superposition of views in
a is a view showing the first step in the alignment procedure. Camera at zero degrees.
b is a view showing the second step in the alignment procedure. Camera at 180 degrees.
c is a view showing the first step of the alignment procedure as seen on the display screen.
d is a view showing the second step of the alignment procedure as seen on the display screen. Pointer is moved to the half-error position.
e is a view showing the alternative second step of the alignment procedure as seen on the display screen. Point moves to the half-error position.
f is a view showing the final step of the alignment procedure as seen on the display screen.
The designer and the manufacturer of a pointing device shown in
Continuing with
Contrary to the previous art, the Applicant has discovered that it is possible to build a pointing device capable of extreme concentricity without making all parts of the device concentric. Instead of making an attempt to make all parts concentric, it is possible to rely solely on the axial symmetry created by the rotation of the machine on which the pointing device is used or on an axial symmetry created by rotating the pointing device itself in a manner concentric with the axis of symmetry or any axis of interest on the machine on which the pointing device is used. To be able to rely on the rotational symmetry the interface to the machine has to be as perfectly concentric as possible. One embodiment of such an interface is a known class, NIST traceable round plug gage used as a shank for the pointing device. For example an X class plug gage has a maximum runout of only 40 microinches. A typical precision used in the industry is 0.001 inch, i.e., the runout is 50 times lower. Plug gages of even higher than X class are readily available and relatively inexpensive.
In the present invention the camera-based pointing device has to meet two requirements: (1) extreme concentricity of the interface to the machine, i.e., the shank and (2) that the axis of symmetry of the shank intersects with the camera's sensor within the optically active area of the sensor. The second requirement is so easy to meet that it is mentioned here only to achieve completeness of the invention's description. Based on the present invention it is thus possible to manufacture pointing devices at a very low cost and with a lifetime performance guarantee, i.e., until the precision shank wears off and the device looses the capability to interface in a concentric manner with the machine on which it is used.
a shows a ray of light 40 creating an image 41 of the target point 30 on the surface of the image sensor 14. The target point 30 is at the intersection of the axis of rotation of the machine or any axis of interest along which the pointing device itself is rotated. The point 30 is the point at which an ideally concentric pointing device would point. Due to the axial symmetry created by rotation along the axis 100 the position of the image 41 on the surface of the image sensor 14 does not change as the pointing assembly is rotated along the axis 100.
b shows the situation after the pointing assembly 10 has been rotated by 180 degrees as shown by the arrow 42. As explained earlier in the absence of a spindle 11 and/or the toolholder 12 the pointing device itself, i.e., its shank could be rotated along the axis of rotation 100 with the same result.
If the target point 30 is not aligned with the axis of rotation the image of the target point would no longer remain at a fixed position on the surface of the image sensor when the pointing device is rotated.
The objective of the alignment method is to align the target point with the axis of rotation and to mark the position of the view of the image of the target on the display 20 as the center point of rotation as observed on the display. Both the target and the on-screen pointer have to be moved in order to accomplish the alignment. The target point can be moved in the camera view by moving the table holding the workpiece on the machine. If a computer is used for displaying the image from the camera used in the pointing device the on-screen pointer can be easily moved using a mouse, or a touchpad, or other pointer positioning input device. If a specialized system is used for displaying the image it has to provide means for marking a specific position on the screen either by using a pointer such as but not limited to a crosshairs or by changing attributes of the point on the display such as, but not limited to, the color or the brightness of a point, or making it blink.
Since the alignment method relies on rotating the pointing assembly or the pointing device itself by 180 degrees it helps to have marks on the body of the pointing device to show zero, item 61 in
c shows the view of the image of the target point 52 on the display 20 when the pointing device is at 0 degree position. The on-screen pointer 62 has been moved to the same position. This creates the initial state in the alignment procedure. The user rotates the pointing device or its assembly to the 180 degree position. If the pointing device and/or the target are misaligned the image of the target point 53 shifts to a new location on screen. Now, the user has a choice to either make an adjustment of the on-screen pointer position 62,
If the rotation used during the alignment procedure was exactly 180 degrees and the camera had no optical distortions the final alignment shown in
Since the main objective behind the present invention was to build low-cost but precise pointing devices the preferred embodiment of the present invention is the simplest possible—a low cost camera placed on an extremely concentric shank combined with the pointer-based on-screen pointer position alignment method as this version of the method does not require any position readout for the machine's table, i.e., can be used on any machine.
Lexicographic definition: extremely concentric shank is a camera shank exhibiting a radial symmetry that has a runout at least an order of magnitude smaller than either the resolution of the camera sensor mounted on the said shank or the required concentricity of the pointing device in case the required concentricity is less restrictive than the sensor's resolution.
This application claims the benefit of the Provisional Application No. 60/940,448 filed on May 28, 2007.
Number | Date | Country | |
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60940448 | May 2007 | US |