Radiant energy – Photocells; circuits and apparatus – Temperature control of photocell
Reexamination Certificate
1998-12-04
2001-01-30
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Temperature control of photocell
C250S559100, C250S559400, C340S501000
Reexamination Certificate
active
06180939
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to machine vision equipment, and more particularly, relates to an apparatus and method for temperature compensation of three-dimensional measurements from a non-contact sensor in a workpiece manufacturing station.
Demand for higher quality has pressed manufacturers of mass produced articles, such as automotive vehicles, to employ automated manufacturing technology to assemble, weld, finish, gauge and test manufactured articles. Machine vision is a key part of today's manufacturing environment. Machine vision systems are used with robotics and as in-process gauging equipment to monitor and improve the manufacturing process and thereby improve quality and reduce cost of the articles produced.
In a typical manufacturing environment, there may be a plurality of different non-contact sensors, such as optical sensors, positioned at various predetermined locations within the workpiece manufacturing, gauging or testing station. The workpiece is placed at a predetermined, fixed location within the station, allowing various predetermined features of the workpiece to be examined by the sensors. Preferably, all of the sensors are properly positioned and carefully calibrated with respect to a fixed frame of reference, such as a common reference on the workpiece or at the workstation.
Achieving high quality manufactured parts requires highly accurate, precisely calibrated machine vision sensors. Not only must a sensor have a suitable resolution to discern a manufactured feature of interest, the sensor must accurately measure with respect to an external frame of reference so that relevant data regarding the manufactured parts can be reported.
One area of concern with sensor accuracy is measurement variations caused by temperature changes at the workpiece manufacturing station. Typically, the entire manufacturing assembly facility will experience significant fluctuations in temperature throughout the workday. As the temperature changes, the entire workpiece manufacturing station changes, including each of its various components. It may be possible to model the response of each component of a workstation with respect to changes in temperature. For instance, it is known that all of the components that comprise the inspection station: the workpiece, the tooling that transports and secures the workpiece in the station, the sensor mounting structure, the sensor mounting hardware, and the sensors, will expand and contract with temperature variations and that these physical changes in the components of the workstation will also cause deviations in the resulting measurements. Consequently, the enormity of the task of accurately modeling each of the relevant components in the typical manufacturing workstation can be readily appreciated.
Therefore, rather than attempting to empirically develop suitable compensation data to correct the response of each workstation component, a temperature compensation system of the present invention employs a system approach. Each of the components of the workstation that may be affected by variations in temperature are viewed as a system. A characteristic curve is determined that represents resulting variations in a sensor's measurements caused by changes in temperature. In this way, the characteristic curve incorporates all of the variables in the system that may affect a measurement from that particular sensor and thus provides an accurate means for providing temperature compensation for the sensor measurements.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a temperature compensation system is provided for compensating measurements from a sensor. A temperature transducer is placed in close proximity to a manufacturing workstation as a means of measuring the ambient temperature associated with the workstation. A reference workpiece is placed within a sensing zone of the sensor. The system includes a temperature compensating module that is connected to the sensor and to the temperature transducer for determining a baseline measurement of the reference workpiece at a reference temperature. The temperature compensating module is further adapted for collecting a plurality of measurements of the reference workpiece over a plurality of temperatures for establishing a relationship between these measurements and their corresponding temperature values. In addition, a workpiece measuring module is also connected to the sensor and to the temperature transducer for measuring a first workpiece at a first temperature, whereby the sensor measurement is compensated for temperature using this relationship. Rather than compensate for ambient temperature changes, the temperature compensation system may also be adapted to compensate measurements based on process driven temperature changes.
REFERENCES:
patent: 4949469 (1990-08-01), Wachtler
patent: 5446971 (1995-09-01), Neumann
Christensen Jesper
Greer Dale R.
Markey, Jr. Myles
Tenniswood Stephen James
Harness & Dickey & Pierce P.L.C.
Le Que T.
Perceptron, Inc.
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