Planar normality sensor

Details Planar normality sensor Planar normality sensor

1999-08-31

2001-12-04

Cuchlinski, Jr., William A. (Department: 3664)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Robot control

C356S614000

Reexamination Certificate

active

06327520

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to sensors using a laser and optical detector, and more particularly, this invention relates to a sensor that determines 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 sensor for determining the planar inclination of a surface.
It is still another object of the present invention to provide a sensor for determining the planar inclination of a surface that is part of an integral sensor device.
In accordance with the present invention, a sensor determines planar inclination of a surface and includes a sensor body having a light emitting end. Three Z-axis sensors are positioned within the sensor body. Each Z-axis sensor includes a laser assembly having a light output for emitting a light beam from the light emitting end onto a surface to be scanned. An optical detector receives the scattered light back that had been emitted from the laser assembly onto the surface to be scanned. A processor is operatively connected to the optical detectors for calculating the planar inclination of the surface based on the light scattered back from the surface. In one aspect of the present invention, the laser beams are generated parallel to each other and parallel to the longitudinal axis of the sensor body.
The sensor can include a sine wave generator, such as a digital signal processor, for generating a sine wave modulation for a laser assembly, wherein each laser assembly has a sine wave modulation that is different from the sine wave modulation of a respective other laser assembly. However, it should be understood that the invention is not limited to sine wave modulation. The sine wave modulation can be a function of amplitude, frequency modulation, DC offset, time and phase. In one aspect of the present invention, the laser assemblies can be positioned within the sensor body at a spaced-apart angle of about 1200° with respect to each other.
Each optical detector can be positioned at an angle with respect to the longitudinal axis of the sensor body and to each laser assembly. Each optical detector includes a position sensitive detector and a lens for directing light scattered from the surface to be scanned into the position sensitive detector. The sensor body further comprises a lower housing section that contains the laser assemblies and the lens of each optical detector, and a mid-section that contains each position sensitive detector.
In still another aspect of the invention, the mid-section can further comprise an inside surface having a mirror adjacent each respective position sensitive detector for creating an optical lever and increasing the effective distance that the sensor can be used. An upper section can include a preamplifier connected to each position sensitive detector. Each optical detector can also comprise a narrow bandpass interference filter. Each laser assembly can include a laser diode, beam circularization optics and beam focusing optics. The sensor body is preferably cylindrically configured.
In still another aspect of the present invention, a sensor body is used with a sensor that determines the planar inclination of a surface. The sensor body includes a body member defining a longitudinal axis and having a light emitting end. The body member includes a lower section having three orifices for receiving laser optic assemblies within each orifice. Three other orifices receive receiver optics. A mid-section has a chip seat that receives a position sensitive detector on which scattered light is impinged. An upper section mounts a preamplifier connected to each laser assembly. The mid-section includes an inside surface having a mirror surface adjacent each chip seat for creating an optical lever. The sensor body includes three orifices on the lower section that receives laser optic assemblies and are positioned at a spaced-apart angle of about 1200 with respect to each other.


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