Optics: measuring and testing – Position or displacement – Triangulation
Reexamination Certificate
2002-10-28
2004-10-19
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Position or displacement
Triangulation
C356S606000, C356S003060
Reexamination Certificate
active
06806968
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for measuring such as, for example, a coordinate measuring apparatus or a machine tool which includes a control and evaluation unit and a measuring sensor. The measuring sensor operates independently of said control and evaluation unit and can be displaced with a mechanism along three coordinate directions relative to a workpiece, which is to be measured. The invention further relates to a method for measuring using such an apparatus.
BACKGROUND OF THE INVENTION
Such an apparatus for measuring can, for example, be a coordinate measuring apparatus or a machine tool. The sensors used in such apparatuses are most often optical probes such as, for example, triangulation probes or video cameras, which include evaluation electronics. For a video camera used as a measuring sensor, the system clock rate of the evaluation electronics is defined by the video frequency of the camera. This frequency is significantly greater than the system clock rate of the control unit of a coordinate measuring system or a machine tool, which is optimized to the drive control. A synchronization of the measuring sensor with the control and evaluation unit without additional special measures can only be achieved if an evaluation is made at standstill of the coordinate measuring apparatus or machine tool, since only then the values of the measuring sensor and the machine measuring values of the coordinate measuring apparatus do not vary in time. However, performing a big measuring task in this way requires a tremendous amount of time, since for the recordation of each measuring point the coordinate measuring apparatus has to come completely to standstill.
To overcome this problem, complicated interfaces have been developed between the control and evaluation unit of a coordinate measuring apparatus or machine tool and a measuring sensor functioning independently of such control and evaluation unit.
Such coordinate measuring apparatus is described in U.S. Pat. No. 5,982,491, which is incorporated herein by reference. This United States patent discloses a laser triangulation probe mechanism which functions independently from the coordinate measuring apparatus and can be moved by the mechanics of a coordinate measuring apparatus along the coordinate directions x, y, z for detecting the edges on workpieces. For this purpose, the measuring sensor is guiding a probe beam on a circular scanning line and the coordinate measuring apparatus mechanism guides the measuring sensor perpendicularly over the edge. To synchronize the sensor values of the measuring sensor, which have been evaluated, with the machine measuring values of the scales of the coordinate measuring apparatus, both the coordinate measuring apparatus and the measuring sensor include an interface, which is especially developed for the measuring sensor used. Via this interface, the measuring sensor informs the control unit of the coordinate measuring apparatus on how many electronic cycles ago the measuring sensor was in a defined position with respect to the edge which has been traversed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an apparatus for measuring having a control and evaluation unit and a measuring sensor, which functions independently from the control and evaluation unit but which can be easily synchronized therewith. It is another object of the invention to provide a method for measuring using such an apparatus.
The apparatus of the invention is for measuring a workpiece and includes: a control and evaluation unit generating machine measuring values (x
i
, y
i
, z
i
) which includes a first timer; a measuring sensor detecting sensor measuring values (x′
i
, y′
i
, z′
i
) and including a second timer; the first and second timers operating independently of each other; the measuring sensor being coupled with the control and evaluation unit; a mechanism operatively connected to the control and evaluation unit for displacing the measuring sensor in three coordinate directions relative to the workpiece in response to the measuring values (x′
i
, y′
i
, z′
i
); and, a synchronizing device for synchronizing the first timer and the second timer.
The method of the invention is for measuring a workpiece using an apparatus including a control and evaluation unit coupled with a measuring sensor and an electromechanical drive mechanism for displacing the measuring sensor in three coordinate directions in relation to the workpiece. The control and evaluation unit includes a first timer and the measuring sensor includes a second timer, the first and the second timer operating independently of each other, the method including the steps of: generating machine measuring values (x
i
, y
i
, z
i
) with the control and evaluation unit; generating the sensor measuring values (x′
i
, y′
i
, z′
i
) with the measuring sensor; and, synchronizing the first timer and the second timer.
The basic concept of this invention is to provide timers in the measuring sensor and in the control and evaluation unit which function independently of each other. The timers are synchronized to a common start time point.
The important advantage of such a coordinate measuring apparatus or machine tool over the prior art is that such coordinate measuring apparatus allows to synchronize in a simple way measuring sensors, which function independently of the coordinate measuring apparatus, with the control and evaluation unit of the coordinate measuring apparatus or the machine tool. In this way, a very simple standard can be provided, which can be taken over by the manufacturers of the corresponding measuring sensors without any big effort. Furthermore, it is also possible to update in a very simple way old measuring sensors, which do not have this standard, just by adding a small program section. This standard provides decisive advantages also for the manufacturers of coordinate measuring apparatuses and machine tools. On the one hand, the often time and cost intensive adaptation of a coordinate measuring apparatus or a machine tool to a specific measuring sensor type hereby is unnecessary. On the other hand, the variety of sensors usable on a coordinate measuring apparatus or a machine tool can be increased considerably.
As a timer in the measuring sensor and in the control and evaluation unit, the timer present in the system having the highest resolution should be used. As an example, this means for a personal computer, the clock counter register for the cycle interrupt source should be used or, for a microprocessor, the time stamp counter register should be used. This is necessary because relatively small time increments are required. The system clock of a personal computer, for example, which provides only for 18 time increments per second, is not sufficiently accurate for this purpose.
The synchronization of the timers to a common starting point can be done in different ways. Most simply, the time values of the timers are read out at a certain time and stored as the start time point. In a preferred embodiment, the timers are synchronized to values, which represent a common clock time. Preferably, the timers should be set to world time as is the case in so-called radio clocks.
To make the running deviations between the timers as small as possible, the timers should be synchronized several times during a measuring sequence at short time intervals to a common start time point.
The time relation of the time values outputted by the timers relative to each other can be determined in a very simple embodiment, in that, at a certain time point after the start point, the common time values of the timers are read out again and the difference of these time values to the corresponding time values at the start time point is determined. The quotient of these differences indicates the ratio of the run time of the timers relative to each other.
Preferably, the timers are normalized to a common time unit such as, for example,sa second. In this way, the time
Carl-Zeiss Stiftung
Font Frank G.
Nguyen Sang H.
Ottesen Walter
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