Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
1998-08-05
2001-02-27
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
C702S153000
Reexamination Certificate
active
06195620
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and devices for determining the geometry of a raw cylinder head casting for use in predicting volume of the chambers of a finished cylinder head.
BACKGROUND ART
A raw cylinder head casting is typically finished by machining the deck face and valve seat surfaces to prepare it for installation of spark plugs and valves. Variations in the volume of the combustion chamber have a strong effect on the variation of the compression ratio of the cylinder. Differences in compression ratio between cylinders of the same engine lead to engine noise vibration harshness (NVH). Differences in compression ratio among engines of the same family require using a less than optimum engine calibration for the engine, in order to meet emissions, which reduces power and adversely affects fuel economy. Thus, it is desirable to know and control the volume of a combustion chamber for a finished cylinder head.
The most common method for measuring the volume of a combustion chamber is to first perform the finish machining and then measure the volume of liquid required to fill the chamber. The method involves covering the combustion chamber with a glass plate having a small hole therethrough. The combustion chamber is carefully filled with liquid, which is accurately measured. This method only measures the volume of finished combustion chambers and is laborious and lacks repeatability. Further, this method will not work with an as cast cylinder head, since it requires a totally enclosed volume, i.e., the combustion chamber must contain both valves and spark plug. By being able to predict the finished volume soon after the time of casting, it is possible to adjust the casting process to repeatably produce the desired volume.
One known technique involves predicting the volume of a finished combustion chamber from a raw cylinder head casting as disclosed in “Method of Predicting Volume of Finished Combustion Chambers From a Raw Cylinder Head Casting,” filed Jan. 21, 1997, having Ser. No. 08/787,506, now U.S. Pat. No. 5,864,777 the disclosure of which is hereby incorporated in its entirety. In this method, laser scanning is used to create a computer model of the cylinder head geometry. A computer technique called “virtual machining” is then used to emulate the real world machining process and transform the computer model of the raw casting to that of a finished combustion chamber. The volume of the computer model is calculated using numerical techniques.
Gathering data from a raw cylinder head casting utilizing laser scanning involves scanning the combustion chamber surfaces and cast locators, which are used for machining purposes. Laser scanning the cast locators, however, becomes difficult since some of the cast locators are positioned vertically to the deck face of the casting. Since these features are difficult to collect with a non-contact scanner, it is difficult to compute the transformation matrix utilized in the virtual machining process described above.
DISCLOSURE OF THE INVENTION
It is thus a general object of the present invention to provide a method and device for accurately gathering data representing the cylinder head geometry, including non-planar surfaces, utilizing non-contact scanning techniques.
In carrying out the above object and other objects, features, and advantages of the present invention, a method is provided for capturing data representative of a geometry of a raw cylinder head casting in order to obtain a casting scanning coordinate system for use with a machining coordinate system. The method includes determining planar data corresponding to planar cast locators disposed on the casting, determining vertical data corresponding to the vertical cast locators disposed on the casting utilizing planar locating features located at predetermined positions with respect to the vertical cast locators, and determining a transformation matrix defining a relationship between the scanning coordinate system and the machining coordinate system based on the planar and vertical data.
In further carrying out the above object and other objects, features, and advantages of the present invention, a device is also provided for carrying out the steps of the above described method. The device includes a planar surface having planar areas corresponding to the planar cast locators. The device also includes planar locating features disposed on the planar surface at predetermined positions with respect, to the vertical cast locators. The device rests on the surface of the raw cylinder head casting during a non-contact scanning so that planar and vertical data may be obtained for use in determining a transformation matrix which defines a relationship between the scanning coordinate system and the machining coordinate system.
The above object and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
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Ebenstein Samuel Edward
Falk Kevin Andrew
Assouad Patrick
Drouillard Jerome R.
Ford Global Technologies Inc.
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