Abstract:
A measuring device for detecting dimensions of bores has a light source emitting a light beam and a beamsplitter for splitting the light beam into a reference beam and a measuring beam. A reference mirror is arranged downstream of the beam splitter. The measuring beam is supplied to a measuring location of the bore and reflected on it. The reference beam is supplied to the reference mirror and reflected on it. The reflected beams are temporally incoherent and are recombined on the beamsplitter to form a recombined beam supplied to a receiver. Reference mirror and receiver have a lateral displacement relative to an optical axis of the measuring device, or the reference mirror is arranged laterally adjacent to the optical axis and the beam splitter at a slant to the optical axis. The measuring device is integrated into a tool or connected to a tool receptacle.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a measuring device for detecting dimensions of test samples, in particular, of hollow bodies, preferably of recesses in workpieces. 
   2. Description of the Related Art 
   When manufacturing bores, seats, and the like in workpieces, it is necessary that the bores have a precise diameter. For this reason, the bores are measured with corresponding measuring devices after the drilling process. When imprecise dimensions are detected, after machining is required. 
   SUMMARY OF THE INVENTION 
   The invention has the object to configure the measuring device of the aforementioned kind such that measuring is possible with great precision. 
   According to the present intention, this object is solved for a measuring device of the aforementioned kind according to a first configuration in that the measuring device can be integrated into a tool or, in place of a tool, can be connected to a tool receptacle and comprises at least one light source whose light beams are divided by a beamsplitter into a reference beam and a measuring beam, of which the measuring beam forming a measuring arm can be supplied to a measuring location of the test sample and the reference beam forming a reference arm can be supplied to a reference mirror, wherein the temporally incoherent beams reflected on the measuring location and on the reference mirror are recombined on the beamsplitter and supplied to a receiver, and wherein the reference mirror and the receiver have a lateral displacement relative to the optical axis of the measuring device. According to a second configuration, this is achieved in that the measuring device can be integrated into a tool or, in place of a tool, can be connected to a tool receptacle and comprises at least one light source whose light beams are divided by a beamsplitter into a reference beam and a measuring beam, of which the measuring beam forming a measuring arm can be supplied to a measuring location of the test sample and the reference beam forming a reference arm can be supplied to a reference mirror, which is positioned laterally adjacent to the optical axis of the measuring device, wherein the temporally incoherent beams reflected on the measuring location and on the reference mirror are recombined on the beamsplitter and can be supplied to a receiver, and wherein the beamsplitter is arranged at a slant to the optical axis of the measuring device. 
   With the measuring device according to the invention according to claim  1  the dimensions of test samples, for example, the diameter of bores in workpieces can be determined with high precision but still in a simple fashion. The beam which is emitted by the light source is divided by the beamsplitter into a reference beam and into a measuring beam. While the measuring beam is deflected to the measuring location on the test sample, the reference beam is deflected to a reference mirror. After reflection on the measuring location or the reference mirror, both beams are recombined and guided to the receiver. Because of the superposition of the beams, an interference contrast results based on which the desired information in regard to the measured dimension of the test sample can be obtained. 
   Since the reference mirror and the receiver in regard to the optical axis of the measuring device have a lateral displacement, the reference mirror and the receiver are thus not positioned on the optical axis but are positioned adjacent thereto. With such a configuration, a very high measuring precision can be obtained. 
   In the measuring device according to claim  5  the beamsplitter is positioned at a slant to the optical axis of the measuring device. In this case, only the reference mirror is arranged adjacent to the optical axis of the measuring device while the light source and/or the receiver can be positioned on the optical axis. 
   Further features of the invention result from the additional claims, the description, and the drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be explained in the following in more detail by means of an embodiment illustrated in the drawing. It is shown in: 
       FIG. 1  in a schematic illustration and in section a tool and a device according to the present intention; 
       FIG. 2  an optical schematic of the measuring device according to  FIG. 1 ; 
       FIG. 3  in a schematic illustration the function of the measuring device; 
       FIG. 4  a measuring signal which has been recorded with the measuring device; 
       FIG. 5  an information flow schematic of the measuring device according to the invention arranged in a tool. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   By means of the tool, dimensions on workpieces, preferably of bores, can be measured simply and precisely. The measuring device provided for this purpose is arranged in the tool which can be, for example, a drilling tool or a thread milling cutter. With the measuring device it is also possible to measure groove depth or the bore depth in a workpiece. The measurement can be carried out during the machining operation performed by the tool. As a result of the measurement, the tool and/or the workpiece to be machined can be adjusted online until the nominal result is achieved. The machining result, for example, roundness of a bore or its diameter, is preferably directly measured and evaluated during machining. In this way, machining errors can be detected and corrected immediately. The finishmachined workpiece does not require any additional check. Since a correction can be performed during machining, very short machining times and primarily excellent product qualities can be obtained. Also, the tool service life is utilized optimally because, as a result of the online measurements and online evaluation during machining, the tool can be used for machining for the optimal length of time. 
   It is also possible to perform with the tool machining on workpiece and to measure and evaluate directly subsequently thereto the machining result. When the machining result does not conform to the desired requirements, directly subsequently thereto the tool and/or workpiece movement is corrected by the required amount and after machining is performed. 
     FIG. 1  shows a schematic illustration of a milling tool  1  with a shaft  34 . By means of the tool a bore is drilled into a workpiece  2  as is known in the art. The tool  1  is embodied as a hollow body in which a measuring device  4  is arranged. It has a housing  5  in which most of the elements of the measuring device  4  are arranged so as to be protected. It can be moved by means of a linear drive  6  in the axial direction of the tool  1 . The tool  1  has near the free end at least one window  7  through which in a way to be described in the following a measuring beam can exit the tool  1  and reach the measuring location  8 . In the illustrated embodiment, it is provided in the wall  9  of the bore  3 . 
   The measuring device  4  has a light source  10  which is embodied as a broadband light source and advantageously is in the form of an LED. The light source  10 , for example, can also be comprised of a halogen lamp, a superluminescent diode, a laser diode and the like. Downstream thereof, a beamsplitter  11  is provided for deflecting the light emitted by the light source  10  to a lens system  15 . It is comprised of a collimator  16 , a lens  17 , and an intermediately positioned beamsplitter  18 . On it a portion of the beam is reflected to a reference mirror  14 . The lens system  15  is positioned on the axis of the measuring device  4 . The reference mirror  14 , the light source  10 , and the beamsplitter  11  are positioned outside of the optical axis of the measuring device  4 . 
   The lens system  15  is illustrated in a simplified fashion. The beam path within the lens system  15  can deviate from the optical axis. 
   The lens system  15  has arranged downstream thereof a deflection mirror  19  for deflecting the light beam  28  passing through the beamsplitter  18  through the window  7  in the tool  1  to the measuring location  8  in the bore wall  9 . 
   As illustrated in  FIG. 1 , the measuring device  4  has an interferometer  31  which is arranged in the housing  5 . The deflection mirror  19  is outside of the housing  5  which is axially slidably supported by means of a linear bearing  20  in the tool  1 . 
   The light emitted by the light source  10  is deflected on the beamsplitter  11  to the lens system  15 . By means of the beamsplitter  18 , a light beam  27  is reflected to the reference mirror  14  where this light beam is reflected back to the beamsplitter  18 . The light beam  28  allowed to pass through the beamsplitter  18  is guided to the deflection mirror  19  which guides the light beam onto the measuring location  8 . The light beam is then reflected back to the deflection mirror  19 . The light beam  28  is then deflected from here to the beamsplitter  18 . 
   By means of the beamsplitter  18 , the light beam  27  reflected by the reference mirror  14  and the light beam  28  coming from the deflection mirror  19  are recombined and then guided to a receiver  13 . It is an opto-electrical receiver, for example, in the form of a photo diode. The receiver  13  is positioned outside of the optical axis of the measuring device  4 . Accordingly, the combined light beams  27 ,  28  are deflected on the beamsplitter  11  to the receiver  13  as an interference beam. 
   The light beams  27 ,  28  received by the receiver  13  are now supplied to an analog-to-digital converter  21  whose converted digital signals are then evaluated by a computer  22  ( FIG. 5 ) arranged downstream. The signal evaluation can be performed in an analog way. 
   The receiver  13  can also be an intelligent photosensor array with signal broadening, for example, including A/D conversion and/or signal amplification. The obtained signals can be guided directly to the computer. 
   Since the bore wall  9  is to be measured about its periphery by interference measurement, the measuring device  4  provided with the interferometer  31  is rotated. It is possible to rotate the measuring device  4  within the tool  1  wherein, depending on the desired measuring precision, the measuring device  4  is rotated about certain rotational angles. Subsequently, the described interference measurement is performed. As soon as the measuring result has been evaluated in the computer, the measuring device  4  is rotated by the next angular step. In this way, the entire periphery of the bore wall  9  can be measures step-wise. In this case, a corresponding number of windows  7  is provided. 
   It is also possible to measure the entire tool  1  with the measuring device  4  at a constant speed and to measure continuously during the course of rotation. 
   The analog/digital converter  21  receives via an angle sensor  25  and the clock generator  26  arranged downstream the required clock signals. An angle sensor is not required when the angular position or the rate of angular movement of the machine tool can be preset precisely. 
   After a complete rotation of the tool  1  or of the measuring device  4 , the measuring device, by means of the linear drive  6 , or the tool  1 , by means of the drive of the machine tool, is moved by the desired amount so that the light beam exiting from the window  7  of the tool  1  impinges on a different peripheral plane of the bore wall  9 . The linear movement of the measuring device  4  or of the interferometer  31  is realized by a motor  6  ( FIG. 5 ) arranged downstream of the computer  22  ( FIG. 5 ) and controlled by the computer by means of a motor drive  24 . The linear movement of a sensor head  33  generated by the linear drive  6  and guided in the linear bearing  20  is measured by a travel measuring system  35  and also controlled by it. The travel measuring system  35  is arranged within the tool  1 . In the described way, the tool  1  and/or the measuring device  4  is rotated about its axis in order to measure the bore wall  9  in the new axial position. In this way, the bore wall  9  can be measured across a part of its axial length or even across its entire axial length. 
     FIG. 5  shows schematically also the data transmission from the rotating measuring system to the stationary computer  22 . The data and energy transmissions of the rotating measuring system  4  to the stationary computer  22  and the motor drive  24  is carried out bidirectionally and, as is known in the art, is realized by inductive coupling  32  with sending and receiving parts as well as rotating and stationary antennas.  FIG. 1  shows a further system location where the coupling  32  can be provided, i.e., on the shaft of the tool. 
   Inasmuch as the measuring location  8  is located on the desired diameter, the two beam paths of the reference and measuring arms  27 ,  28  are of the same size. The measuring signal, which in  FIG. 4  is shown in an exemplary fashion, has a maximum in this case. In the diagram according to  FIG. 4  the intensity is plotted against the distance. Based on the position of the maximum of the interference contrast, the radius of the bore  9  can be determined. The intensity of the measuring signal results in a way known in the art according to the following equation:
 
|(Δ s )= I   0 {1 +m y   21  (Δ s ) cos (2 π/λ·Δs+φ} 
 
with the following meaning:
     m=modulation factor   Y 21 =bidirectional degree of coherence   λ=average wavelength   Δs=optical distance difference   φ=material-dependent phase jump.   

   The modulation factor m depends on the light intensity and the reflection factor. At the maximum of the interference signal ( FIG. 4 ) the optical distance difference Δs is zero. By means of the measuring device  4  the optical distance difference Δs between the reference beam  27  and the measuring beam  28  is tuned by moving the beamsplitter  18  in the direction of the measuring beam  28 , and the interference contrast ( FIG. 4 ) detected in this way is evaluated. For example, when the measuring location  8  deviates from the desired diameter, the measuring beam  28  has a different length than the reference beam  27  which has a constant length. The sensor head  33  is moved across the entire measuring area and the interference signal is recorded in this way. Subsequently, the interference maximum is determined as a function of the traveled distance. Based on this, the diameter of the bore can be determined. 
   Smaller shape deviations can be detected by moving the reference mirror  14  and recording the corresponding travel distance. In this connection, the interference signal is also recorded and the interference maximum evaluated as a function of the travel distance. 
     FIG. 3  shows the principal function of the measuring device  4 . The light emitted by the light source  10  is divided by the partially transmissive mirror  18  into the reflected beam  27  and into the passing beam  28 . The reflected beam  27  reaches in the described way the reference mirror  14  on which it is reflected back onto the splitter mirror  18 . The passing beam  28  impinges on the measuring location  8  where it is reflected. The two partially coherent beams  27 ,  28  are recombined on the splitter mirror  18  and cause interference. The two combined beams then reach the receiver  13 . The evaluation of the interference contrast enables a resolution of less than 1 μm. 
   In the described measuring device  4  the light source  10 , the receiver  13 , and the reference mirror  14  are not positioned on the optical axis of the measuring device, but are separated by a lateral displacement. This arrangement reliably prevents particularly reflections. 
   In a further embodiment (not illustrated), the beamsplitter  18  is positioned slantedly. In this case, only the reference mirror  14  is positioned adjacent to the optical axis. The light source  10  and the receiver  13  in this case can be arranged on the optical axis of the measuring device.