JP2006337148A - On-machine shape-measuring apparatus and working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-machine shape-measuring apparatus capable of measuring the surface shape of a work piece, while and making it contact the measurement probe at low-contact pressure. <P>SOLUTION: The on-machine shape measuring apparatus 30 measures the vibration components in the locked state of a servo-motor before starting the measurement (S14), sets up the notch filter 66 for removing the vibration components (S18), removes the machine vibration components in the locked state etc., of the servomotor by the set notch filter 66 (S20) from the output of a linear scale 44, after starting the measurement. Thereby, even if the measurement probe 32 goes into a state of light contact with the workpiece, the state of the probe is apt to receive the effects of the machine vibration, high-accuracy shape measurements can be realized, by removing the machine vibration component and canceling the effects. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a shape measuring instrument having a probe that contacts an object to be measured with a low contact force, and preferably relates to an on-machine shape measuring instrument mounted on a processing machine having a plurality of servo motors.

2. Description of the Related Art Conventionally, a shape measuring instrument for measuring the surface shape of an optical lens or the like has a contact pressure as small as possible so as not to damage a measured object. As a shape measuring device with a reduced contact pressure, for example, Patent Document 1 discloses a shape measuring device that holds a measurement probe in the direction of gravity and adjusts the contact pressure by balancing gravity with a spring or the like. Further, Patent Document 2 discloses a shape measuring instrument in which the contact pressure on the object to be measured is reduced by tilting and holding the measurement probe.
JP-A-7-260471 JP 2005-502876 gazette

However, when the measuring probe is brought into contact with the object to be measured with a low contact force, there is a problem that the on-machine shape measuring instrument cannot measure with high accuracy due to mechanical vibration from the processing machine mounted. When operating an on-machine shape measuring instrument on a processing machine, servo lock control is performed to stop the servo motor at a specific position. The servo motor is microscopically before and after the command position even in the servo lock state. The rotation continued, and the vibration from the servo motor etc. was superimposed on the signal of the measuring instrument and became an error, which hindered high precision measurement. This vibration differs depending on the servo lock position of the servo motor, and the characteristics of the servo motor change over time, making it difficult to cope with it.

Here, in the existing on-machine shape measuring instrument, in order to deal with the above error, a moving average is added to the shape measurement error, or smoothing processing is performed by a low-pass filter or the like. This hindered accurate measurement.

The present invention has been made in order to solve the above-described problems, and the object of the present invention is an on-machine shape capable of measuring the surface shape of an object to be measured with high accuracy while bringing the probe into contact with a low contact force. To provide a measuring instrument.

In order to achieve the above object, the shape measuring instrument 30 according to claim 1 includes a probe 32 that contacts the surface of the object to be measured with a low contact force,
An on-machine shape measuring instrument 30 mounted on a processing machine 10 having a plurality of servo motors 22, 24, 26, and a position detector 44 for measuring the position of the probe.
Frequency analysis means 62 for measuring vibration components in the locked state of the servo motors 22, 24, 26;
Filter setting means 62 for setting a filter 66 for removing the vibration component measured by the frequency analysis means;
The present invention is characterized by comprising vibration component removing means 66 for removing the vibration component in the locked state of the servo motor by the filter 66 from the output of the position detector.

The on-machine shape measuring device 30 of the first aspect measures a mechanical vibration component in a locked state of the servo motor and sets a filter for removing the vibration component. Then, the mechanical vibration component in the locked state of the servo motor or the like is removed from the output of the position detector by the set filter. For this reason, even if it is in a state where it is easily affected by mechanical vibration by bringing the probe into contact with a low contact force, it eliminates the mechanical vibration due to the lock of the servo motor, etc. Measurement can be realized.

The on-machine shape measuring instrument 30 according to claim 2 compares the output of the position detector from which the vibration component is removed with the design shape value to obtain a shape error, and corrects the machining data from the obtained shape error. Since the mechanical vibration due to the lock of the servo motor or the like is removed and highly accurate shape measurement is performed, highly accurate machining to a desired shape can be realized using machining data corrected based on the measurement result.

The on-machine shape measuring instrument 30 of claim 3 is supported by the support means 42 with an inclination θ so that the measuring probe 32 moves backward by its own weight. On the other hand, the urging means 40 urges the measurement probe 32 to protrude toward the object to be measured W. For this reason, the contact force of the measurement probe 32 to the object W to be measured is a difference between the retreating force due to the weight of the measurement probe 32 with an inclination and the urging force of the urging means 40. It is possible to adjust so that it may become small. At the same time, even if it is in a state that is easily affected by mechanical vibration by bringing the probe into contact with a low contact force, high-precision shape measurement is achieved by eliminating the mechanical vibration due to the lock of the servo motor and canceling the influence. Can be realized.

The on-machine shape measuring instrument of claim 4 can measure the vibration of the mechanical system including the workpiece and the measuring element without using a special vibrometer (for example, an acceleration pickup). As a result, measurement on the user side is possible, and it is possible to cope with aging of mechanical vibration.

Since the processing machine according to claim 5 is provided with an on-machine shape measuring device capable of removing mechanical vibration components, high-precision shape measurement is realized by removing mechanical vibration caused by a servo motor lock or the like. Is possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an ultra-precision machine equipped with a shape measuring instrument according to an embodiment of the present invention.
The ultra-precision machine 10 includes a workpiece fixing base 12 for fixing a workpiece W, a grinding wheel shaft 14 for holding a tool 16, a servo motor 22 for feeding the grinding wheel shaft 14 in the X direction, and a servo motor 24 for feeding in the Y axis direction. And a servo motor 26 for feeding in the Z-axis direction. A shape measuring device 30 for measuring the shape of the workpiece W by the measuring probe 32 is provided along with the grindstone shaft 14.

The configuration of the shape measuring instrument 30 will be described with reference to the plan view of FIG.
The shape measuring instrument 30 includes a main drive cylinder 34 urged by an air cylinder 40 and a driven cylinder 36 connected to the main drive cylinder 34 by a bracket 38. A measurement probe 32 is attached to the driven cylinder 36. The main cylinder 34 and the driven cylinder 36 are supported in an inclined state by an air bearing 42. That is, the air bearing 42 is supported with a slight inclination so that it cannot be recognized by the naked eye so as to move backward (toward the left in the figure) by the weight of the main cylinder 34 and the driven cylinder 36. The driven cylinder 36 is provided with a linear scale 44 as a position detector. The shape measuring instrument 30 is configured such that the stroke of the driven cylinder 36 is set to 10 mm, and the measurement pressure can be adjusted in the range of several tens mgf to several hundreds mgf as described later. In this embodiment, the main cylinder 34 and the driven cylinder 36 are provided to prevent the columnar cylinder from rotating.

With reference to FIG. 3, the contact force (measurement pressure) F of the measurement probe 32 in the shape measuring instrument 30 of the embodiment will be described.
In the shape measuring instrument 30 of the present embodiment, the air bearing 42 supports the driven cylinder 36 having the measurement probe 32 and the main driving cylinder 34 so as to move backward with the inclination θ. The friction force of the air cylinder 40 is very small. Here, the retreating force of the driven cylinder 36 and the main driving cylinder 34 is generated by the inclination θ in the air bearing and becomes mgsigθ which is much smaller than the own weight m. On the other hand, the air cylinder 40 urges the measurement probe 32 with a pushing force Fc so as to protrude toward the workpiece W side. For this reason, the contact force F of the measurement probe 32 to the workpiece W is set such that the driven cylinder 36 and the main cylinder 34 supported by the air bearing 42 with an inclination θ and the retraction force due to the own weight m (measurement element own weight inclination component) mgsigθ. And a difference (F = Fc−mgsigθ) from the pushing force Fc of the air cylinder 40, the contact force F can be adjusted to several tens of mgf so as to be very small. For this reason, it is possible to measure without deforming the surface of an object to be measured which is easily deformed, such as aluminum products and resin products.

In the shape measuring instrument 30 of the present embodiment, since the air cylinder 40 that biases the measurement probe 32 by air pressure is used, the biasing force applied to the measurement probe 32 can be easily adjusted. That is, in the shape measuring instrument 30 of the present embodiment, the measurement pressure of the measurement probe 32 can be continuously changed by changing the urging force (pushing force Fc) of the air cylinder 40, and thereby the workpiece having a complicated shape. By measuring the surface shape while changing the measurement pressure of the measurement probe 32, the measurement can be realized with high accuracy. Even if the measurement pressure is changed, the position where the measurement probe is in contact with the workpiece W does not change.

As described above, when the contact force of the measurement probe 32 is lowered, the on-machine shape measuring instrument is easily affected by mechanical vibration generated in the processing machine. For this reason, in the on-machine shape measuring instrument 30 of this embodiment, the process which removes mechanical vibration is performed. The control configuration of the on-machine shape measuring instrument 30 will be described with reference to FIG.

The shape measuring device 30 is connected to a pneumatic device 50 that generates air pressure and a cylinder air pressure control device 52 that adjusts the air pressure supplied to the air cylinder 40 of the shape measuring device 30. The air pressure from the pneumatic device 50 is configured to be supplied directly to the air bearing 42. The output from the linear scale 44 is input to the amplifier unit 60. The amplifier unit 60 measures the frequency analysis means 62 that performs frequency analysis of mechanical vibrations of the processing machine 10 before the start of measurement, the notch filter 66 that removes the analyzed mechanical vibrations, and the shape of the object to be measured. The shape data (shape signal) measured by the shape measuring means 64 is output to the shape analyzing means 68 after the mechanical vibration is removed through the notch filter 66. The shape analysis means 68 obtains the difference between the design shape of the object to be measured (workpiece) held in the shape data holding means 67 and the measured shape. From the difference obtained by the shape analysis means 68, the shape error calculation means 72 calculates the shape error, and a correction value for correcting the calculated shape error is calculated by the correction value calculation means 74, thereby correcting the machining error. NC data for processing is created by the NC creation means 76.

Next, shape measurement by the on-machine shape measuring instrument 30 will be described with reference to FIGS.
FIG. 5 is a flowchart showing the shape measurement processing by the shape measuring instrument.
The processing machine 10 is stopped, that is, the servo motors 22, 24, and 26 are set in the servo lock state while the workpiece W that has been processed by the tool 16 shown in FIG. S12). In this state, the measurement probe 32 is pressed against the workpiece W by the shape measuring instrument 30, and the mechanical vibration component superimposed on the workpiece W is measured from the linear scale 44 (S14). The measured signal LS from the linear scale 44 (the vibration component is shown in FIG. 6A) is subjected to fast Fourier analysis at 120 Hz, for example, and the frequency component of the vibration (mainly vibration caused by the servo lock of the servo motor) is analyzed. (S16). Then, the peak frequency is searched for from the result of the frequency component analysis, stored as a mechanical vibration frequency, and a notch filter 66 for removing the mechanical vibration frequency is generated (S18). The characteristic of the notch filter 66 attenuates the mechanical vibration frequency component as shown in FIG. The preparation for shape measurement is completed by the above processing. Since the mechanical vibration component varies depending on the servo lock position of the servo motor, the characteristics of the notch filter 66 vary depending on the servo lock position.

The shape measurement is started (S20). Here, the scanning moving stage (processing machine control axis) is driven, and the measurement surface of the workpiece W is moved in the Y-axis direction by the measurement probe 32 as shown in FIG. Scan. Since the measurement probe 32 moves following the shape of the workpiece W, the locus of the measurement probe 32 at that time becomes the shape of the workpiece W. This measured shape is shown in FIG. The waveform of the measured shape is superimposed with the mechanical vibration due to the servo lock of the servo motor, etc., so that the notch for removing the mechanical vibration frequency component analyzed as described above with reference to FIG. By passing the filter 66, data having the shape shown in FIG. 7C from which mechanical vibration has been removed is obtained. Next, the measured shape is subjected to coordinate transformation so that the vertex of the shape matches the origin of the coordinate as shown in FIG. 8A (S22).

Here, FIG. 8B shows a design value (design shape, for example, an aspherical polynomial for lens design) of the workpiece. The shape analysis is performed by comparing the design value of the workpiece with the measured shape after coordinate conversion shown in FIG. 8A (S24), and the difference between the designed value and the measured shape is obtained to calculate the shape error ( S26). FIG. 8C shows the calculated shape error.

Subsequently, a value for correcting the shape error is calculated (S28), and finally machining NC data for correcting (correcting) the shape error is created (S30). For example, when processing an optical lens, the absolute dimension is not important, and it is necessary to accurately create a relative curved surface shape. For example, if there is a part that is excessively cut, NC data for precisely creating a relative curved surface shape is created by creating machining data that cuts other parts that protrude beyond that part. By processing the workpiece W again on the processing machine 10 side using the created NC data, processing into a desired shape is realized.

The on-machine shape measuring instrument 30 of this embodiment measures a mechanical vibration component in a locked state or the like of the servo motors 22, 24, and 26 before starting measurement, and sets a notch filter 66 that removes the vibration component. Then, the mechanical vibration component in the locked state of the servo motor or the like is removed from the output of the linear scale 44 by the set notch filter 66. For this reason, even if the measurement probe 32 is brought into contact with a low contact force (for example, several tens of mgf), even if the measurement probe 32 is easily affected by the mechanical vibration, the mechanical vibration due to the servo motor lock or the like is removed and the influence is canceled out. Thus, highly accurate shape measurement can be realized.

Furthermore, by carrying out before the start of measurement, vibration can be removed according to the machine state at that time and corresponding to the secular change of the processing machine. It is possible to deal with various objects to be measured such as the size of workpieces and workpiece materials. Furthermore, since a special mechanical vibrometer (for example, an accelerometer) is not required, the user of the on-board shape measuring instrument can measure the vibration component at any time.

The on-machine shape measuring instrument 30 of this embodiment compares the output of the linear scale 44 from which the vibration component is removed with the design shape value to obtain a shape error, and generates machining data from the obtained shape error. Since the mechanical vibration due to the lock of the servo motor or the like is removed and highly accurate shape measurement is performed, highly accurate machining to a desired shape can be realized using machining data generated based on the measurement result.

The on-machine shape measuring instrument 30 of the present embodiment supports the measurement probe 32 with an inclination θ so as to retreat by its own weight by an air bearing 42. On the other hand, the air cylinder 40 urges the measurement probe 32 to protrude toward the workpiece W side. For this reason, the contact force of the measurement probe 32 to the workpiece W is a difference between the retraction force due to the weight of the measurement probe 32 with an inclination and the biasing force of the air cylinder 40, so the contact force becomes very small. It is possible to adjust as follows. At the same time, even if the measuring probe 32 is brought into contact with a low contact force, even if the measuring probe 32 is easily affected by mechanical vibration, the mechanical vibration due to the lock of the servo motor, etc. is removed and the influence is canceled out, thereby achieving a highly accurate shape. Measurement can be realized.

In the embodiment described above, in the above-described embodiment, an example is given in which the measurement probe is applied to an on-machine shape measuring device in which the contact force is reduced by supporting the measurement probe with a tilt in the direction of retreating by its own weight. Needless to say, the above configuration can be applied to various on-machine shape measuring instruments having a contact with reduced contact force. In the above-described embodiment, the notch filter is configured by software. However, the notch filter may be configured by hardware.

In the embodiment described above, the measurement probe is operated so as to follow the shape of the workpiece W. However, the measurement probe position can be kept constant and the machine control axis can be operated according to the machining program. is there. At this time, the variation of the measurement probe position corresponds to a processing error.

It is a block diagram which shows the structure of the ultraprecision processing machine carrying the shape measuring device which concerns on one Embodiment of this invention. It is a top view of an on-machine shape measuring device. It is explanatory drawing which implement | achieves a contact pressure with an on-machine shape measuring device. It is a block diagram which shows the control structure of an on-machine shape measuring device. It is a flowchart which shows the measurement process by an on-machine shape measuring device. (A) is a graph which shows the mechanical vibration component analyzed by the on-machine shape measuring device, (B) is a graph which shows the frequency characteristic of a notch filter. (A) is explanatory drawing of the shape measurement by the measurement probe of a workpiece | work, (B) is explanatory drawing which shows the shape data on which the mechanical vibration component was superimposed, (C) is the shape which removed the mechanical vibration component. It is explanatory drawing which shows data. (A) is explanatory drawing which shows the shape data after coordinate transformation, (B) is explanatory drawing which shows the design shape of a workpiece | work, (C) is explanatory drawing which shows a shape error.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Super precision processing machine 30 Shape measuring device 32 Measuring probe 34 Main drive cylinder 36 Followed cylinder 40 Air cylinder 42 Air bearing 44 Linear scale 60 Frequency analysis means 66 Notch filter 72 Shape error calculation means 76 NC preparation means W Workpiece (measurement object)

Claims (5)

A probe that contacts the surface of the object to be measured with a low contact force;
An on-machine shape measuring instrument equipped with a position detector for measuring the position of the probe, and mounted on a processing machine having a plurality of servo motors,
Frequency analysis means for measuring a vibration component in the locked state of the servo motor;
Filter setting means for setting a filter for removing the vibration component measured by the frequency analysis means;
An on-machine shape measuring device comprising: vibration component removing means for removing a vibration component in a locked state of the servo motor by the filter from the output of the position detector. A shape error analyzing means for comparing the output of the position detector from which the vibration component has been removed by the vibration component removing means and the design shape value to obtain a shape error;
2. The on-machine shape measuring instrument according to claim 1, further comprising machining data correction means for correcting machining data from the obtained shape error. A supporting means for supporting the measuring element with an inclination angle with respect to a horizontal plane so as to retract the measuring element by its own weight;
The on-machine shape measuring instrument according to claim 1 or 2, further comprising biasing means for biasing the measuring element toward the object to be measured. The apparatus according to any one of claims 1 to 3, wherein the frequency analysis means measures the vibration component in the locked state of the servo motor by bringing the probe into contact with the surface of the object to be measured. Upper shape measuring instrument. A processing machine comprising the on-machine shape measuring instrument according to any one of claims 1 to 4.

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