Method of determining the planar inclination of a surface

Details Method of determining the planar inclination of a surface Method of determining the planar inclination of a surface

1999-08-31

2001-07-10

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Angle measuring or angular axial alignment

Relative attitude indication along 3 axes with photodetection

C356S370000, C356S152200, C702S153000

Reexamination Certificate

active

06259519

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of sensing surfaces, and more particularly, this invention relates to a method of determining the planar inclination of a surface.
BACKGROUND OF THE INVENTION
Machine vision systems can be used in workpiece treating and handling systems, such as in a mechanism where a robot arm places a part onto another piece as in automobile manufacturing systems. For example, the robot arm may have to place a part onto a body surface at an angle with respect to that surface. Thus, the planar inclination must be known to allow a motion control device to align to that inclination or some predetermined angle relative to the planar surface.
Some robot assemblies, such as used in the automotive industry, automatically determine the position and attitude of a three-dimensional body at a workstation by using three separate cameras to generate non-overlapping planes of image data. These cameras also target a single point of the body without the use of structured light. Locations of target points are determined and processed within a programmed computer, together with calibration data relating to the expected position of the body in the workstation. An example includes the structure and system disclosed in U.S. Pat. No. 4,639,878 to Day et al.
Usually three cameras or other sensors are used because Euclidian geometry requires a minimum of three points to determine space and position. For example, a work position detection apparatus as disclosed in U.S. Pat. No. 4,831,561 to Utsumi, uses a complicated system of at least three separate, one-dimensional mechanical sensors for generating outputs dependent on the detected position of the work.
In other systems, three different laser beams generate three different colored light beams, which converge into a single light spot on a surface, such as for placing a circuit board into a position at predetermined, incident angles. The three different colored light beams are emitted from circular light sources. The light is reflected from the electronic part or other object and received by pick-up devices. In U.S. Pat. No. 5,298,977, light sources are emitted respectively with the three different colored lights and are arranged so that the light beams converge to a single spot on the surface of the circuit board to detect quantatively the height and incline angle of an electronic part mounted on the circuit board. It also detects a configuration of a mirror surface of an electronic part for the light. However, the use of colored lights in some applications could interfere with each other and cross talk could result.
Other sensors and imaging systems used for workpiece treating or handling include those systems disclosed in U.S. Pat. Nos. 5,331,406 and 4,819,167, such as used for determining the precise location of a moving object. A semiconductor wafer position could be determined relative to a destination position. Also, integrated circuits could be accurately positioned upon surface mounted circuit boards.
However, the above devices and systems typically use separate devices that are spaced apart from each other without a housing or other structure, which are part of a compact integral unit. These sensors described above are typically used to detect the position of a workpiece or object in simple robotic applications.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of determining the planar inclination of a surface.
It is still another object of the present invention to provide a method for determining the planar inclination of a surface using a sensor that is part of an integral sensor device.
In accordance with the present invention, a method determines the planar inclination of a surface and comprises the steps of modulating each three lasers positioned in a sensor body with a different sine wave frequency based on stored values within a wave-table by superimposing onto the emitted light beam from each laser a respective sine wave frequency. The light beam is emitted from each laser onto a surface to be analyzed. The method further comprises the step of scattering the light beam emitted from each laser onto a respective position sensitive detector formed from a semiconductor chip that is positioned within the sensor body. Each light beam is demodulated by producing electrical signals from each respective position sensitive detector corresponding to the position of the scattered light beam. The electrical signals are integrated by values in the wave-table to obtain demodulated values. The planar inclination of the surface is calculated based on the demodulated values.
In another aspect of the present invention, the method further comprises the step of generating the sine wave frequency within a digital signal processor. The method can also comprise the step of operating the digital signal processor in discrete time and phase locking with the scattered light beam signals. The step of calculating can further comprise the step of integrating over a base frequency. The sine wave frequencies can be produced at frequencies that are prime relative to each other. The method can further comprise the step of producing electrical signals by producing two signals corresponding to respective sides in the position sensitive detector.


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