JP2008241571A - Profile measuring device and method for controlling profile measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a profile measuring device capable of setting the control of contact load of a measuring probe in the optimum condition, by considering an object to be measured, profile data of an edge end of a measuring probe and physical characteristics. <P>SOLUTION: The profile measuring device includes a displacement measuring means for measuring a push-in amount of a measuring probe 1; a contact load storing means for storing relation of the push-in amount and the contact load of the measuring probe 1; a physical information storing means for storing the object to be measured, the profile data of the edge part of the measuring probe 1 and a physical constant; a contact load calculation means for calculating the contact load of the measuring probe 1 from the stored profile data and the physical constant and an allowable range of the contact load; and a control mechanism 8 for controlling the push-in amount of the measuring probe 1 so that the contact load of the measuring probe 1 is in the contact load calculated with the contact load calculation means and the allowable range of the contact load based on the relationship of the push-in amount and the contact load of the measuring probe 1 stored to the contact load storing means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a contact-type shape measuring apparatus and a method for controlling the shape measuring apparatus.

  As a contact-type shape measuring apparatus for measuring the shape of the object to be measured, for example, Patent Document 1 describes. Here, FIG. 6 is a diagram showing the configuration of the shape measuring apparatus described in the publication.

  This shape measuring apparatus includes a measuring probe 101, an optical displacement meter 102, a laser length measuring device 104, and a contact load measuring means 105. Here, the measuring probe 101 has a stylus 100 for measuring the shape of the object to be measured, as shown in FIG. The optical displacement meter 102 measures the pushing amount of the measuring probe 101 (hereinafter, the pushing amount means the displacement of the measuring probe). The laser length measuring device 104 measures the position of the measurement probe 101 on each axis. The contact load measuring means 105 measures the contact load of the measurement probe 101.

  In this shape measuring apparatus, the shape can be measured with the contact load of the measuring probe 101 fixed to the object to be measured by the contact load control, so that the measurement accuracy can be improved.

Here, if the contact load of the measurement probe 101 with respect to the object to be measured becomes too large, the elastic deformation of the object to be measured becomes large and an accurate shape cannot be measured. In some cases, the surface of the object to be measured may be damaged.
In such a case, in order to keep the contact load as constant as possible, it is conceivable to strictly control the servo mechanism that controls the pressing amount of the measurement probe. That is, it is conceivable to improve the robustness of the measurement probe with respect to the object to be measured so that any object to be measured can be measured under the condition that the contact load is constant.
JP 2004-108959 A

  However, in such a measurement probe with improved robustness, vibration noise due to excessive servo control is added to the measurement result in order to strictly control the push-in amount of the measurement probe regardless of the object to be measured. A problem arises that the measurement accuracy becomes worse due to the ease. In addition, measurement conditions are limited regardless of the object to be measured, such as limiting the measurement speed.

  This invention is made | formed in view of this situation, The place made into the objective is providing the control method of the shape measuring apparatus which can improve a measurement speed and measurement accuracy, and a shape measuring apparatus.

In order to solve the above problems, the invention described in claim 1 of the present invention includes a measurement probe,
Displacement measuring means for measuring the pushing amount of the measuring probe, contact load storing means for storing the relationship between the contact load applied to the measuring probe and the pushing amount, the object to be measured, and the tip of the measuring probe Physical information storage means for storing the shape data and physical constants of
A contact load calculating means for calculating a contact load of the measuring probe and an allowable range of the contact load from the shape data and physical constant stored in the physical information storage means;
The contact load of the measurement probe calculated by the contact load calculation means and the contact load based on the relationship between the pressing amount of the measurement probe stored in the contact load storage means and the contact load And a control means for controlling the pushing amount of the measurement probe so as to fall within the allowable range.

According to a second aspect of the present invention, there is provided a shape measuring device for measuring the surface shape of the object to be measured at the scanned position by bringing the measuring probe into contact with the surface of the object to be measured with a predetermined contact load. Control method,
Measuring the relationship between the pressing amount of the measurement probe and the contact load, storing the measurement data in the contact load storage means, and the shape data and physical constants of the object to be measured and the tip of the measurement probe; From the step of storing in the physical information storage means, the object to be measured and the shape data and physical constants of the measurement probe stored in the contact load storage means, the contact load of the measurement probe and the allowable range of the contact load And the contact load of the measurement probe calculated by the contact load calculation means based on the relationship between the pressing amount of the measurement probe stored in the contact load storage means and the contact load. And a step of controlling the pushing amount of the measuring probe so as to fall within an allowable range of the load and the contact load.

  In the shape measuring apparatus and the method for controlling the shape measuring apparatus according to the present invention, the optimum contact load and the allowable range of the contact load according to the object to be measured are determined from the shape data and physical constants of the object to be measured and the tip of the measurement probe. Calculated. Then, using the calculation result, it is possible to optimally control the pressing amount of the measurement probe and the control range of the pressing amount. Therefore, according to the shape measuring apparatus and the method for controlling the shape measuring apparatus of the present invention, the followability of the measurement probe is optimized, so that the measurement speed and measurement accuracy can be increased.

Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a side view of the shape measuring apparatus of the present invention. FIG. 2 is a block diagram showing the relationship between the control means and the computer which is the contact load calculation means in the present invention. FIG. 3 is a block diagram showing the internal configuration of the computer. FIG. 4 is a graph showing the relationship between the pressing amount of the measurement probe and the contact load. FIG. 5 is a flowchart showing the operation of the control method of the shape measuring apparatus of the present invention.

  As shown in FIG. 1, the shape measuring apparatus of the present invention includes a measuring probe 1, a dead weight canceling mechanism 2, a servo motor 3, a length measuring unit 4, a detecting unit 5, an XY moving mechanism 6, and a pressure. A sensor 7, a control mechanism 8, and a computer 9 are included.

The measurement probe 1 has a contact portion for measuring the shape of the object to be measured. The dead weight canceling mechanism 2 is for canceling the dead weight of the probe, and for example, a leaf spring is used. The servo motor 3 moves the measurement probe 1 in the Z-axis direction of the detection axis via a ball screw. The length measuring unit 4 that is a length measuring means measures the position of the measurement probe 1 in the Z-axis direction. The detection unit 5 serving as detection means measures the amount of pressing of the measurement probe 1 and is constituted by, for example, a linear scale. The XY moving mechanism 6 that is a control means moves the object to be measured in the X-axis direction or the Y-axis direction orthogonal to the Z-axis. The pressure sensor 7 measures the contact load of the measuring probe 1 and is detachable from the XY moving mechanism 6. Therefore, the pressure sensor 7 is used only when measuring the relationship between the pressing amount of the measuring probe 1 and the contact load, and is removed from the XY moving mechanism 6 when it disturbs the shape measurement. The control mechanism 8 is a control means for servo-controlling the position of the measurement probe 1.
Further, as shown in FIG. 2, a detection unit 5, a length measurement unit 4, and a pressure sensor 7 are connected to the computer 9. Then, a signal is input from each component to the computer 9. A control mechanism 8 and an XY movement mechanism 6 are also connected so that a control signal can be sent from the computer 9.

  The computer 9 has a function as a contact load calculation unit, and also includes a contact load storage unit that is a contact load storage unit and a physical information storage unit that is a physical information storage unit.

  The contact load storage unit inputs and stores the relationship between the amount of pressing of the measurement probe 1 and the contact load that is the output value of the pressure sensor 7 as data. An example of data stored in the contact load storage unit is shown in FIG. Note that the data stored here may be actually measured data, or linear approximation and polynomial approximation data.

  The physical information storage unit stores shape data and physical constants with respect to the object to be measured and the tip of the measurement probe 1. The contents stored in the physical constant storage unit are physical constants such as Young's modulus, Poisson's ratio, Vickers hardness, yield pressure, friction coefficient, and surface shape design formula of the object to be measured. Further, a design formula for the shape of the tip of the measurement probe 1 and physical constants such as Young's modulus, Poisson's ratio, Vickers hardness, yield stress, and friction coefficient can be input and stored. Needless to say, the physical information storage unit can store physical information of a plurality of objects to be measured and measurement probes.

  Further, the computer 9 calculates the contact load and the allowable range of the contact load by using data and physical constants stored in the physical information storage unit. For example, the computer 9 calculates a contact load that falls within the elastic deformation limit of the object to be measured and an allowable range of the contact load from a general Hertz contact formula. Alternatively, in order to prevent the measured object from being plastically deformed and scratched during the measurement, the optimum contact load for the measured object and the allowable range of the contact load are calculated. The elastic deformation limit is a state immediately before the object to be measured undergoes plastic deformation. In addition, within the elastic deformation limit is a state in which the object to be measured does not cause plastic deformation.

  Further, the computer 9 determines the pushing amount of the measuring probe 1 and the optimum control range of the pushing amount. This determination is made based on the relationship between the calculated optimum contact load, the allowable range of the contact load, and the pressing amount of the measurement probe 1 stored in the contact load storage unit and the contact load. Based on this determination, the control mechanism 8 sends a drive signal to the servo motor 3 to control the push-in amount of the measurement probe 1.

  The details of the determination will be described below using mathematical formulas for calculation contents in the computer 9.

  First, as an initial condition, an allowable value of elastic deformation in the object to be measured is set. For example, numerical calculation conditions such as a condition for measuring an object to be measured within the elastic deformation limit and a condition for allowing an elastic deformation amount to 10 nm or less are set.

  In addition, as initial conditions, if conditions for the friction between the object to be measured and the probe for measurement and conditions for controlling the atomic force due to the difference in atoms are set, generally known physics suitable for them Use the formula.

  Next, the contact load of the measurement probe 1 and the allowable range of the contact load are calculated. Here, explanation will be made using a general Hertz contact formula. First, each coefficient such as Young's modulus of the measurement probe and the object to be measured is expressed as follows.

The physical constant and shape of the tip of the measurement probe are as follows.
E1: Young's modulus ν1: Poisson's ratio R1: Design radius

The physical constant and shape of the object to be measured are as follows.
E2: Young's modulus ν2: Poisson's ratio R2: Design radius σy2: Yield stress

And the contact load etc. which are calculated are described as follows.
W: Contact load Pmax: Theoretical maximum contact load P: Theoretical contact load τmax: Maximum shear stress (τmax = σy2 / 2)
δ: elastic deformation amount a: radius of contact area

Calculated according to the Hertz contact formula:
a = {3/4 · W [(1-ν12) / E1 + (1-ν2) / E2] ×
[(R 1 · R 2) / (R 1 + R 2)]} 1/3 (1)
Pmax = 3W / (2πa2) (2)
P = Pmax × (1−x2 / a2) 1/2 (3)
δ = {9/16 · W2 [(1-ν12) / E1 + (1-ν22) / E2] 2 ×
[(R 1 + R 2) / (R 1 · R 2)]} 1/3 (4)
τmax = S × Pmax (5)
In the equation (5), S = 0.614−0.234 × (1 + ν 2)
It is.

  Here, it is assumed that the object to be measured is a soft glass material such as plastic. In such a soft glass material, the surface may be damaged by the contact load of the measurement probe during measurement. In such a case, the contact load of the measurement probe and the allowable range of the contact load are determined according to the following calculation conditions.

The conditions for calculating the contact load of the measuring probe in the elastic deformation region and the allowable range of the contact load are as follows.
τmax ≦ σy2 / 2
From equation (5), Pmax = τmax / S
∴ Pmax ≤σy2 / (2S)
It becomes.

Also,
A = (1-.nu.12) / E1 + (1-.nu.22) / E2.
B = (R1 · R2) / (R1 + R2)
Then, from equation (2), Pmax = 3W / (2πa2)
Therefore, from the formula (1), 3W = Pmax × 2π × ((3/4) · W · A · B) 2/3
3W / W2 / 3 = Pmax × 2π × ((3/4) · A · B) 2/3
3 (W) 1/3 = Pmax × 2π × ((3/4) · A · B) 2/3
W = [(2π / 3) × Pmax × ((3/4) · A · B) 2/3] 3
It becomes.

Further, when the safety factor k and the marginal contact load (safe contact load) Ws are taken into consideration for W, the actual contact load Wk is calculated by the following equation.
Wk = kW ± Ws (6)
Here, the marginal contact load (safe contact load) Ws is an auxiliary parameter for making the theoretical value and the actually measured value more coincident. The marginal contact load (safe contact load) Ws is set to an empirical value when the object to be measured is actually scratched or defective. This marginal contact load (safe contact load) Ws is usually zero.

  The following example is an example in which the amount of elastic deformation of the object to be measured is set to 10 nm or less as an initial condition. A method for determining the contact load of the measurement probe 1 and the allowable range of the contact load in this example will be described below.

When the elastic deformation amount of the object to be measured is δ and the allowable amount is Δδ,
From the equation (4) δ = {9/16 · W2 [(1-ν12) / E1 + (1-ν22) / E2] 2 ×
[(R1 + R2) / (R1 · R2)]} 1/3
It becomes.

here,
A = (1-.nu.12) / E1 + (1-.nu.22) / E2.
B = (R1 · R2) / (R1 + R2)
Then, δ = ((9/16) · W2 · A2 / B) 1/3
δ / W2 / 3 = ((9/16) · A2 / B) 1/3
1 / W2 / 3 = [((9/16) · A2 / B) 1/3] / δ
W = [δ / ((9/16) · A2 / B) 1/3] 3/2
It becomes.

Here, if the allowable amount of the contact load W when the amount of elastic deformation changes by Δδ is ΔW, the above equation is
W ± ΔW = [(δ ± Δδ) / ((9/16) · A2 / B) 1/3] 3/2
It becomes.

From the above, the contact load and the allowable range of the contact load are obtained as W ± ΔW.

  Next, a method for determining the push amount of the measurement probe and the control range of the push amount will be described.

  The pressing amount of the measuring probe and the control range of the pressing amount are determined by the computer 9 and the relationship between the pressing amount of the measuring probe and the contact load stored in the contact load storage unit as shown in FIG. It is determined from the result of the calculated contact load and the allowable range of the contact load.

  For example, when the calculated contact load is 50 mgf and the allowable range of the contact load is ± 10 mgf, as shown in FIG. 4B, the push amount of the measurement probe is L1 mm, and the push amount control range. Is ± Δ1 mm. Further, when the contact load is 20 mgf and the allowable range of the contact load is ± 5 mgf, as shown in FIG. 4C, the push amount of the measurement probe is L2 mm, and the control range of the push amount is ± Δ. 2 mm.

  Next, the determined pushing amount of the measurement probe and the control range of the pushing amount are sent to the control mechanism 8 as a control signal. The control mechanism 8 sets the movement amount of the servo motor 3 and control parameters (for example, position loop gain and speed loop gain in the servo control loop) based on this control signal. Based on this setting, the servo motor 3 can be driven to bring the measuring probe 1 into contact with the object to be measured with a pushing amount L1 mm (in the case of FIG. 4B). Further, during the measurement, the measurement probe 1 is controlled so that the change in the push amount is within ± Δ1 mm.

  According to the present embodiment, the pressing amount of the measuring probe and the control range of the pressing amount are determined in consideration of the elastic deformation amount of the object to be measured. Therefore, according to the hardness of the object to be measured, the pressing amount of the measurement probe can be set appropriately, and the control range of the pressing amount can also be set appropriately. As a result, the followability of the measurement probe is optimized, so that the measurement speed can be increased. In addition, since the control range of the push amount can be set appropriately, vibration noise due to excessive servo control can be reduced.

  Further, the servo here does not have to be closed loop control, and may be open loop control using a pulse motor, for example.

  Next, the control method of the shape measuring apparatus of the present invention will be described based on the flowcharts shown in FIGS.

[Step S01]
First, shape data and physical constants of the object to be measured and the probe for measurement are input, and a contact load and an allowable range of the contact load are calculated according to Equation (6).
When the contact load of the object to be measured is known, the contact load and the allowable range of the contact load are input.

  Next, the process proceeds to the step of measuring the relationship between the pressing amount of the measuring probe 1 and the contact load and storing it in the contact load storage means.

[Step S02]
First, the measurement probe 1 is moved to the upper end of the measurement apparatus. Then, the pressure sensor 7 is disposed on the XY moving mechanism 6 positioned below the measurement probe 1.

[Step S03]
The measurement probe 1 is lowered until it contacts the pressure sensor 7. Whether or not the measurement probe 1 is in contact with the pressure sensor 7 is determined based on a detection result from a detection unit provided in the measurement probe 1. Until the measurement probe 1 comes into contact with the pressure sensor 7, the detection unit 5 indicates zero, but after the contact, the amount of pressing of the measurement probe 1 is indicated.

[Step S04]
After the measurement probe 1 comes into contact with the pressure sensor 7, the pressing amount of the measurement probe 1 and the output value of the pressure sensor 7 are stored in a contact load storage unit in the computer 9. The data to be stored are the push amount when the measurement probe 1 is further pushed and the output value of the pressure sensor 7 at that position.

  Here, when the measuring probe 1 is pushed down to a certain position, the stroke of the limit of the self-weight canceling mechanism is reached, and thus the procedure for storing in the contact load storage unit ends here. In addition, the step for measuring and storing the push-in amount and the contact load of the measurement probe 1 may be performed when the measurement apparatus is started up or when the measurement probe is changed, and needs to be performed for each measurement. There is no.

[Step S05]
After the measurement data of the push-in amount of the measurement probe 1 and the measurement data of the contact load are completed, the push-in amount of the measurement probe 1 and the control range of the push-in amount that are optimum for the measurement object are determined. This determination is made using the result of step S01 and the result of step S04.

For example, when the contact load of the object to be measured is 50 mgf and the control range of the contact load needs to be ± 10 mgf, the pressing amount of the measuring probe 1 and the control range of the pressing amount shown in FIG. The computer 9 determines that the measurement condition is satisfied. Further, when the contact load of the object to be measured is 20 mgf and the control range of the contact load needs to be ± 5 mgf, the pressing amount of the measuring probe 1 and the control range of the pressing amount shown in FIG. It meets the measurement conditions.
Next, the measuring probe 1 is moved to the upper part of the measuring apparatus, the pressure sensor 7 installed on the XY moving mechanism 6 is removed, and an object to be measured (not shown) is installed instead.

[Step S06]
After setting the object to be measured, the measurement probe 1 is brought into contact with the object to be measured. At the time of this measurement, the control mechanism 8 drives the servo motor 3 so that the measurement probe 1 is within the push amount calculated in step S05 and the control range of the push amount.

  After scanning a predetermined measurement area of the object to be measured, the measurement probe 1 is withdrawn, and the measurement of the object to be measured is completed.

  The present invention measures the surface shape of an object to be measured by bringing a measuring probe into contact with the surface of the object to be measured such as a lens or a mirror with a predetermined contact load and detecting the displacement of the measuring probe at the scanned position. The present invention relates to a contact-type shape measuring device and a method for controlling the shape measuring device.

It is a side view of the shape measuring apparatus of this invention. It is a block diagram which shows the relationship between the control means of the shape measuring apparatus of this invention, and the computer which is a contact load calculating means. It is a block diagram which shows the internal structure of a computer. It is a graph which shows the relationship between the pushing amount of the probe for a measurement, and a contact load. It is a flowchart which shows operation | movement of the control method of the shape measuring apparatus of this invention. It is a block diagram of the conventional shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring probe 2 Self weight cancellation mechanism 3 Servo motor 4 Length measuring part 5 Detection part 6 XY movement mechanism 7 Pressure sensor 8 Control mechanism 9 Computer

Claims (2)

A measurement probe;
A displacement measuring means for measuring the pushing amount of the measuring probe;
Contact load storage means for storing the relationship between the contact load applied to the measurement probe and the push-in amount;
Physical information storage means for storing shape data and physical constants of the object to be measured and the tip of the measurement probe;
A contact load calculating means for calculating a contact load of the measuring probe and an allowable range of the contact load from the shape data and physical constant stored in the physical information storage means;
The contact load of the measurement probe calculated by the contact load calculation means and the contact load based on the relationship between the pressing amount of the measurement probe stored in the contact load storage means and the contact load And a control means for controlling the push-in amount of the measurement probe so as to fall within the allowable range. A method for controlling a shape measuring apparatus for measuring a surface shape at a scanned position by bringing a measuring probe into contact with a surface of a measurement object with a predetermined contact load,
Measuring the relationship between the pressing amount of the measurement probe and the contact load, storing the measurement data in the contact load storage means, and the shape data and physical constants of the object to be measured and the tip of the measurement probe; From the step of storing in the physical information storage means, the object to be measured and the shape data and physical constants of the measurement probe stored in the contact load storage means, the contact load of the measurement probe and the allowable range of the contact load And the contact load of the measurement probe calculated by the contact load calculation means based on the relationship between the pressing amount of the measurement probe stored in the contact load storage means and the contact load. A control method for a shape measuring apparatus, comprising: a step of controlling a pressing amount of the measuring probe so as to fall within an allowable range of a load and the contact load.