Optics: measuring and testing – Shape or surface configuration – By focus detection
Reexamination Certificate
2000-10-11
2003-11-11
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
By focus detection
C033S503000, C033S559000, C356S601000
Reexamination Certificate
active
06646750
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and an arrangement for measuring the structures of an object with the help of a scanning element that is allocated to a coordinate measuring device and that starts from a flexible shaft, with the scanning element touching the object and with its position being then determined directly or indirectly with at least one reticule, which is allocated to the scanning element, with an optical sensor.
BACKGROUND OF THE INVENTION
An arrangement of the kind described above is already known (DE 297 10 242 U1). In this familiar arrangement, surface topography of an item or object is measured with a photogrammetry system and the scanning element. The scanning element, e.g. a ball, is arranged at the end of an elastic shaft. In the shaft reticules can be incorporated, whose positions are recorded by the photogrammetry system relative to a tracer reference system. The position of the scanning element is determined e.g. by the reticule positions.
We also know of a measuring system for recording surface topography of objects with a data transmitter, which consists of a tracer pin and a light source of a defined kind at its end. The light source is guided along the outline that is to be recorded. In this method, an optical receiver records the respective position of a light source, which forms a luminous spot or light spot, in a three dimensional Cartesian coordinate system. A computer evaluates the measurement results. As an extension of the tracer pin, the light source takes on the shape of e.g. a concentrically enclosed glass fiber (DE 40 02 043 C2).
We furthermore know of a scanning system for measuring small structures, which is based on quartz crystal that stimulates a glass fiber with scanning element. When it touches the surface of the item, the dampening of the system is evaluated. Although this technique enables small scanning forces, it is subject to a relatively high degree of inaccuracy (measurement error 5 &mgr;m).
And finally, for the purpose of measuring structures, we are familiar with the method of determining the position of a scanning element with the help of a microscope; for this method, a transmission procedure must be applied due to the equipment so that only structures of through-holes or other perforations can be measured.
SUMMARY OF THE INVENTION
The invention at issue is based on the problem of developing a method and a device for measuring surface topography of objects with which any random structure and object of varying surface hardness can be determined with a high degree of measurement exactness.
According to the invention, a method for measuring the structures of an object solves the problem with a scanning element that is allocated to a coordinate measuring device and that starts from a flexible shaft and touches the object and whose position is then determined directly or indirectly with at least one reticule, which is allocated to the scanning element, with a sensor in such a way that, with the exception of a free bending length comprising the scanning element and/or the reticule, the shaft runs within a rigid or basically rigid guiding piece and that the scanning force, which occurs upon contact between the scanning element and the object, is determined from the excursion of the scanning element and/or reticule from a neutral position. In doing so, particularly the scanning force is set to a value that has been adjusted to the properties of the object, due to the specification of the bending length. This can occur through shifting of the shaft within the guiding piece. The scanning force values obtained this way can then be taken into consideration in subsequent measurements of the object's structures.
In the case of some objects, the scanning force has considerable influence on the measuring results. In the invented method, it is possible to adjust the scanning force to the properties of the object, such as surface topography and surface hardness, as a parameter of the measurement.
In a preferred version, the scanning force of the scanning element is determined based on the following equation:
F
=
3
·
E
·
f
·
I
1
3
wherein F describes the scanning force, E the modulus of elasticity of the shaft, l the effective bending length of the shaft between the rigid guiding piece and the scanning element, I the axial surface moment of the shaft, and f the excursion of the latch element from a neutral position. The modulus of elasticity, axial surface or inertia moment and length are specified by the design or material properties of the device and can be summarized into one constant. This makes the scanning force proportional to excursion and it can be determined quickly and without extensive arithmetical operations and time.
If necessary, the shaft can be moved within the guiding piece in order to modify the effective bending length. Apart from this, the rigid guidance of the shaft ensures in a constantly reproducible manner that the shaft has a defined bending length.
In a useful version, the scanning force is adjusted as a controlled variable in a control circuit to a specifiable constant or nearly constant value, with the support of at least one motor being moveable in the form of an actuator. The scanning force in this version can be maintained at a specified value throughout the entire measuring process of the structure. For measuring the surface topography in three dimensions, it has frequently proven useful if the support can be moved by drives in five degrees of freedom with the elastic shaft connected to it. For this purpose, numerical control circuits are suited. In particular, the support is connected with the adjusting mechanism for the optical system into one unit, which can be adjusted with a motor into five degrees of freedom.
Furthermore it is beneficial when the scanning element's excursion is measured with an optical sensor, which records the difference between the scanning element's position when it is in neutral position and the scanning element's position when it touches the surface of the object. It is useful if the sensor, which is the same as the one used for measuring the structure, moves together with the support.
The position of the scanning element and/or of the at least one reticule is determined optically especially with reflective radiation and/or radiation shutting off the element or reticule and/or reflecting from the scanning element. It is useful if the tracer extension or the shaft are a fiber-optic light guide or comprise such a light guide in order to feed the required light to the scanning element or the reticule via this light guide.
It is also possible that the scanning element and/or the reticule have the design of a self-luminescent electronic element such as LED or comprise such a component.
In particular, the invention excels through an arrangement for measuring the structures of objects with the help of a scanning element that is allocated to a coordinate measuring device and that starts from a flexible shaft and can be brought into contact with the object and whose position can then be determined directly or indirectly with at least one reticule, which is allocated to the scanning element, with a sensor, with the arrangement excelling through the fact that the shaft, with the exception of a free bending length comprising the scanning element and/or the reticule, runs in a rigid or basically rigid guiding piece. This specifies the scanning force, defined by the effective bending length, which makes the arrangement adjustable to the conditions of the surface properties of the object that is to be measured.
In particular, the arrangement excels through the fact that a sensor is provided for measuring the excursion of the scanning element and/or of the reticule from a neutral position, that the shaft—with the exception of a free bending length comprising the scanning element and/or the reticule—is run in a rigid or basically rigid guiding piece, that the guiding piece can be moved relative to the object's surface
Dennison, Schultz & Dougherty
Rosenberger Richard A.
Werth Messtechnik GmbH
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