JP3815910B2 - Measuring head and measuring feeler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a measurement head for detecting contact with a measurement object used in a coordinate measuring machine, a machine tool, and the like, and a measurement feeler of the measurement head, and in particular, means for suppressing vibration during measurement. The present invention relates to a measurement head and a measurement feeler.
[0002]
[Prior art]
A measurement head that detects contact with the object to be measured and displacement after the contact includes a measurement feeler that contacts the object to be measured, a feeler support part that supports the measurement feeler, and a detector that detects the displacement of the feeler support part. Prepare. The measurement feeler has a simple linear shape made of a homogeneous material such as metal, carbon or ceramics. The detector includes a touch type by means such as a micro switch for detecting contact with the object to be measured, and a displacement measurement type by means such as a differential transformer for detecting the displacement of the measurement feeler.
[0003]
Such measuring heads are used in measuring machines that measure two-dimensional and three-dimensional shapes. It is also possible to attach this measuring head to the spindle of the machine tool. In this case, the position reading device reads the coordinates of the x-axis, y-axis, and z-axis of the machine tool when it comes into contact with the object to be measured, and the dimensions of the object to be measured, for example, the processed workpiece Measure the dimensions. In this case, for example, the measured dimension is used in order to process again the insufficiently processed part of the workpiece.
[0004]
When a penetrating force is applied by acceleration and stop when positioning or approaching operation is performed, vibration occurs in the measurement feeler and the measurement head. The amplitude of the vibration may be erroneously detected as contact or displacement by the detector of the measuring head. Therefore, it is necessary to take measures against this vibration in order to perform highly accurate measurement.
[0005]
One solution to such vibrations is to attenuate the generated vibrations to a level that does not affect the desired measurement accuracy. A displacement measuring device for damping vibration is disclosed in Japanese Patent Laid-Open No. 5-309551. In this displacement measuring device, the inside of the housing is filled with liquid, a narrow gap is provided around the detection shaft in the housing, and vibration damping is caused by viscous resistance when fluid flows through the gap.
[0006]
Another solution to vibration is to distinguish between deflection of the measurement feeler due to vibration of the measurement machine or machine tool and measurement sensor deflection caused by contact. A signal processing circuit for identifying the deflection of the measurement feeler due to vibration and contact is disclosed in Japanese Patent Laid-Open No. 5187808. In this signal processing circuit, the frequency of erroneous signal identification is reduced by setting two types of threshold values, a relatively low threshold value and a relatively high threshold value, for a signal with respect to deflection.
[0007]
[Problems to be solved by the invention]
Regarding the vibration generated in the measurement head, the above solutions are known, but none of them has a function of suppressing vibration by the measurement feeler alone, and the known measurement feeler is positioned or approached at the time of measurement. It is impossible to suppress the vibration of the measurement feeler generated when the operation is performed and the vibration of the measurement feeler support portion in the measurement head. Therefore, the measurement accuracy or reproducibility of the measurement head is deteriorated, making it difficult to measure the measurement head with high accuracy.
[0008]
An object of the present invention is to provide a measurement head and a measurement feeler that suppress vibrations generated in the measurement feeler during a measurement operation, thereby suppressing vibrations of the entire measurement head and enabling high-precision measurement. That is.
[0009]
[Means for Solving the Problems]
The present invention provides a measurement head and a measurement feeler provided with dynamic stiffness changing means for changing dynamic stiffness in order to suppress vibration during measurement operation to a level that does not adversely affect measurement. The dynamic stiffness changing means improves the dynamic stiffness by imparting vibration damping to the measurement feeler and removing the resonance frequency of the measurement feeler system from the range of frequencies generated during measurement, thereby increasing the measurement stiffness during measurement. The vibration of is reduced below a desired level. The dynamic rigidity can also be increased by increasing the static rigidity.
[0010]
Here, the dynamic rigidity is defined as X / F, where F is a periodic excitation force acting on one applied point of the elastic body, and X is a displacement caused by F at another point of the same elastic body. It is a characteristic. That is, the dynamic rigidity means a property in which vibration due to a fluctuating load and an inertial force does not easily occur. Increasing the dynamic rigidity means reducing the amplitude for all frequencies. The dynamic stiffness changes depending on the static stiffness, the resonance frequency, and the damping coefficient. The larger the static stiffness and the damping coefficient, the higher the dynamic stiffness. Further, if the frequency of the generated vibration deviates from the resonance frequency, the amplitude becomes small.
[0011]
The present invention provides a measurement head including a housing and a measurement feeler supported by the housing and in contact with an object to be measured. A weight is attached to the measurement feeler so as to be movable in the longitudinal axis direction, or the weight is attached to be replaceable. Provided is a measurement head in which the dynamic rigidity of the measurement head is variable .
[0012]
Further, according to the present invention, in the measurement feeler supported by the housing of the measurement head and in contact with the object to be measured , the weight is movably attached in the longitudinal axis direction of the measurement feeler , or the weight is removably attached. to provide a measurement feeler which is adapted.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the measuring head and measuring feeler of the present invention will be described in detail with respect to an embodiment.
FIG. 1 is a schematic diagram showing the concept of an embodiment of the measurement head and measurement feeler of the present invention. Although FIG. 1 shows a touch type measuring head, other types, for example, a displacement measuring type measuring head may be used.
[0014]
The measurement head 11 includes a housing 15 and a measurement feeler 13 supported by the housing 15. The housing 15 includes a feeler support member 17 that supports the measurement feeler 13, a biasing means 19 that biases the feeler support member 17, a fulcrum member 21 against which the biased feeler support member 17 abuts, and the feeler support member 17. A detector 23 for detecting displacement is accommodated. In the case of the touch-type measuring head 11 of FIG. 1, the detector 23 is a microswitch. In the case of the displacement measuring type measuring head 11, the detector 23 is a displacement measuring means such as a differential transformer.
[0015]
The measurement feeler 13 of the present invention includes dynamic stiffness changing means 31 including a spring element 25, a damping element 27, and a mass portion 29. The dynamic stiffness changing means 31 allows the measurement feeler 13 and the measurement feeler 13 and the measurement head 11 to be measured. The dynamic rigidity of the entire measuring head including the biasing means 19 is changed. Specifically, at least one of the physical constants such as the spring constant of the spring element 25, the damping coefficient of the damping element 27, and the mass of the mass portion 29 may be changed.
[0016]
In order to suppress the vibration of the measurement feeler 13 by changing the dynamic rigidity of the measurement head 11, vibration damping is imparted to the measurement feeler 13 system or the resonance frequency of the measurement feeler 13 system is generated during measurement. By removing from the range of the vibration frequency, the vibration generated during measurement may be reduced to a level that does not adversely affect the measurement accuracy. By removing the resonance frequency of the system of the measurement feeler 13 from the range of the vibration frequency generated at the time of measurement, the maximum amplitude within the frequency range that can be generated is lowered, and the apparent dynamic rigidity is improved. Further, since the dynamic stiffness is proportional to the static stiffness under a certain condition, it is possible to improve the dynamic stiffness and suppress the vibration of the system of the measurement feeler 13 by improving the static stiffness.
[0017]
Suppressing the vibration of the measurement feeler 13 leads to suppressing the vibration of the entire measurement head 11 including the measurement feeler 13 and the biasing means 19. Therefore, by suppressing the vibration of the measurement feeler 13, the measurement head 11 can perform measurement with high accuracy.
Hereinafter, a specific embodiment of the dynamic stiffness changing means 31 for suppressing vibration will be described with reference to the drawings.
[0018]
In the following two embodiments, the dynamic stiffness changing means 31 changes the dynamic stiffness of the measurement feeler 13 and the measurement head 11 by mainly changing the vibration damping property of the measurement feeler 13.
FIG. 2 is a side sectional view of the measurement feeler 13 showing the first embodiment of the dynamic stiffness changing means 31. In FIG. 2, a cavity 35 is provided in the measurement shaft 33 of the measurement feeler 13, and a vibration damping material 37 is enclosed in the cavity 35. In this case, as the vibration damping material 37, for example, oil, silicon grease, urethane or the like is used. By enclosing the vibration damping material 37 in the cavity 35, the vibration damping property of the measurement feeler 13 and the measurement head 11 as a whole can be changed, and desired vibration damping property can be imparted to the measurement feeler 13 and the measurement head 11. It becomes possible. For example, vibration is attenuated by fluid friction of oil. Further, by enclosing the vibration damping material 37 in the cavity 35, the mass and internal attenuation of the measurement feeler 13 are changed, thereby changing the resonance frequency and vibration amplitude, and the dynamic stiffness of the measurement feeler 13 and the measurement head 11 is changed. It is also possible to change.
[0019]
FIG. 3 is a side view of the measurement feeler 13 showing a second embodiment of the dynamic stiffness changing means 31. In the embodiment shown in FIG. 3, a vibration damping material 41 is attached to a proximal end portion 39 of the measurement feeler 13 that is a joint portion with the feeler support member 17. In this case, as the vibration damping material 41, for example, rubber or plastic is used. By attaching the vibration damping material 41 to the joint between the feeler support member 17 and the measurement feeler 13, the vibration generated in the measurement feeler 13 is attenuated, and the dynamic rigidity of the measurement feeler 13 and the measurement head 11 is improved.
[0020]
In order to change the dynamic rigidity of the measurement feeler 13, the resonance frequency of the measurement feeler 13 may be changed. In the following two embodiments, the dynamic stiffness changing means 31 mainly changes the resonance frequency of the measurement feeler 13.
FIG. 4 shows a third embodiment of the dynamic stiffness changing means 31, and a weight 43 is added to the measurement feeler 13 as the dynamic stiffness changing means 31. The weight 43 is movable in the longitudinal axis direction 45 of the measurement feeler 13. Preferably, the weight 43 further includes a fixing means 47, for example, a screw, for fixing the weight so as to be movable to an arbitrary position. By changing the mass and position of the weight 43, the resonance frequency of the measurement feeler 13 and the measurement head 11 changes. By changing the mass and position of the weight 43 so that the resonance frequency deviates from the range of the main vibration frequency generated during the measurement operation in the measurement machine or machine tool to which the measurement head 11 is attached, the measurement feeler 13 and the measurement head are changed. 11 can be improved. Since the weight 43 can be removed, the weight can be freely replaced so that the resonance frequency deviates from the main frequency generated at the time of measurement by the measuring machine or machine tool to which the measuring head 11 is attached. . Further, it is possible to easily change the resonance frequency of the measurement feeler 13 and the measurement head 11, that is, to change the dynamic rigidity, by adding a weight 43 to the conventional measurement feeler 13.
[0021]
The weight 43 may be formed in an elongated cylindrical shape. By adopting an elongated cylindrical shape, the static rigidity of the measurement feeler 13 can be partially improved, and thereby the dynamic rigidity of the measurement feeler 13 can be further improved.
The weight 43 may be composed of a plurality of parts, and may be assembled into one when attached to the measurement feeler 13.
[0022]
FIG. 5 shows a fourth embodiment of the dynamic stiffness changing means 31. A cavity 49 is provided inside the measurement shaft 33 of the measurement feeler 13, and a screw thread is provided inside the cavity 49. In FIG. 5, the measurement shaft 33 of the measurement feeler 13 is removable from the proximal end portion 39 of the measurement feeler 13, and the cavity 49 inside the measurement feeler 33 is open at the end 51 of the measurement shaft 33. . An internal screw 53 that is the dynamic stiffness changing means 31 is inserted into the cavity 49 from the end 51 of the measurement shaft 33. By changing the position of the internal screw 53, the resonance frequency of the measurement feeler 13 and the measurement head 11 is changed. As in the case of FIG. 4, the measurement is performed by changing the position of the internal screw 53 so that the resonance frequency deviates from the range of the vibration frequency generated during the measurement operation in the measurement machine or machine tool to which the measurement head 11 is attached. The dynamic rigidity of the feeler 13 and the measurement head 11 can be improved. Further, when the internal screw 53 is long, the static stiffness of the measurement feeler 13 itself is affected. Therefore, the dynamic stiffness can be changed by changing the static stiffness.
[0023]
In FIG. 5, it is possible to provide no thread in the cavity 49 provided inside the measurement feeler 13. In this case, what is inserted into the cavity 49 is a cylindrical body or a cylindrical body instead of the internal screw. Such a cylindrical body or a cylindrical body may be fixed in the cavity by a frictional force.
The dynamic stiffness of the measurement feeler 13 can be changed by changing the static stiffness by changing the mass distribution and spring constant of the measurement feeler 13.
[0024]
FIG. 6 shows an embodiment in which the static stiffness of the measurement feeler 13 is changed. In FIG. 6, in order to change the mass distribution and the spring constant of the measurement feeler 13, the shape of the measurement shaft 33 of the measurement feeler 13 which has been uniform in the past is tapered. By using the tapered shape, for example, the mass distribution and the spring constant can be changed without changing the mass and length of the measurement feeler 13.
[0025]
As described above, according to the present invention, it is possible to easily improve the measurement accuracy of the measurement head 11 by making a simple modification to the measurement feeler 13.
The measurement feeler of the present invention not only suppresses vibration generated in the measurement feeler, but also suppresses vibration of the entire measurement head by applying the measurement feeler of the present invention to the measurement feeler portion of the existing measurement head. , Enabling high-precision measurement.
[0026]
【The invention's effect】
According to the present invention, the measurement feeler is provided with dynamic stiffness changing means to attenuate or dampen the vibration of the measurement feeler caused by the positioning and approaching operation during measurement or the vibration of the feeler support in the measurement head, Improve the measurement accuracy (reproducibility, degree of variation of measurement values) of the measurement head, and enable high-speed and high-accuracy measurement.
[0027]
Furthermore, the measurement accuracy of the conventional measurement head can be improved by using the measurement feeler of the present invention in a measurement head having no conventional damping or damping means.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the concept of an embodiment of a measuring head and a measuring feeler of the present invention.
FIG. 2 is a side cross-sectional view of a measurement feeler showing a first embodiment of dynamic stiffness changing means for mainly imparting vibration damping to the measurement feeler.
FIG. 3 is a side view of a measurement feeler showing a second embodiment of dynamic stiffness changing means for mainly imparting vibration damping to the measurement feeler.
FIG. 4 is a side view of a measurement feeler showing a third embodiment of dynamic stiffness changing means for changing the resonance frequency of the measurement feeler.
FIG. 5 is a side cross-sectional view of a measurement feeler showing a fourth embodiment of dynamic stiffness changing means for changing the resonance frequency of the measurement feeler.
FIG. 6 is a side view of a measurement feeler showing one embodiment for changing the static stiffness of the measurement feeler.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Measuring head 13 ... Measuring feeler 15 ... Housing 25 ... Spring element 27 ... Damping element 29 ... Mass part 31 ... Dynamic rigidity change means

Claims (2)

In a measurement head comprising a housing and a measurement feeler supported by the housing and in contact with an object to be measured,
A measuring head characterized in that a weight is attached to the measuring feeler so as to be movable in the longitudinal axis direction, or a weight is attached so as to be replaceable, and the dynamic rigidity of the measuring head is made variable . In the measurement feeler that is supported by the housing of the measurement head and contacts the object to be measured,
A measurement feeler comprising a weight attached to be movable in the longitudinal axis direction of the measurement feeler , or a weight attached to be exchangeable.

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