JP4557657B2 - Contact type probe and shape measuring device - Google Patents

Description

  The present invention relates to a contact-type probe and a shape measuring device mounted on a shape measuring device for accurately measuring the shape of an optical element such as a lens or a mirror.

  A three-dimensional shape measuring apparatus for accurately measuring the shape of an optical element such as a lens or a mirror is divided into a probe for tracing the shape of the object to be measured and a coordinate position measuring means for measuring the coordinate position of the probe. Can think. At this time, what is important for the probe is to copy the surface position of the object to be measured on a moving member capable of measuring coordinates. An error when the probe traces the surface to be measured is called a trace error. Conventionally, as disclosed in Patent Document 1 and Non-Patent Document 1, as a structure for supporting a contact-type probe, a probe shaft is provided so as to be movable up and down using an air bearing, and the probe's own weight is supported by a spring. The configuration is known.

  When a shape is traced using such a contact type probe, a trace error occurs as described above. Therefore, even if there is a trace error, a sufficiently weak spring, that is, a spring constant is sufficient so as not to cause an error in the pressing force of the probe. A small spring is needed. This is because the amount obtained by multiplying the trace error by the spring constant is an error in the pressing force.

  As another conventional example, Patent Document 2 discloses a method of canceling the weight of a probe using magnetic force. In this method, a magnetic circuit comprising a yoke, a permanent magnet and a coil is provided, the yoke is fixed so as to sandwich the probe, and the weight of the probe is canceled by the magnetic force of the magnetic circuit.

The probe is often called a stylus, a stylus, or a feeler, but in this specification, the probe is unified.
JP-A-6-265340 JP 2003-42742 A Academic Lecture Proceedings P697 of the 1992 Precision Engineering Society Spring Meeting

  However, the above conventional techniques have the following unsolved problems.

  (1) The size of the spring is increased in order to reduce the pressing force. The force generated by the spring is a force obtained by applying a pressing force to the weight of the probe. The pressing force is very small, but the weight of the probe is large. For this reason, the force generated by the spring is relatively large.

  However, as described above, it is necessary to reduce the influence of the trace error. Therefore, it is necessary to reduce the spring constant so that the change in pressing force is small even if there is a trace error. If this is achieved with a mechanical spring as in the conventional example, the length of the spring, that is, the length obtained by dividing the generated force of the spring by the spring constant becomes very long. In other words, a large spring is required.

For example, if the mass of the probe is 10 g and the pressing force is 0.1 mN, the force generated by the spring is F = 9.8 × 10 + 0.1 = 98.1 mN with a gravitational acceleration of 9.8 m / s ² . Further, the allowable pressing force error is 10%, that is, 0.1 × 10/100 = 0.01 mN. Furthermore, if the trace error is 10 μm, the spring constant is K = 0.01 / 10 = 0.001 mN / μm.

  Therefore, the deflection of the spring is F / K = 98.1 mm, and a deflection of about 100 mm is necessary. The size of the spring at this time should be much larger because the length of the spring when no force is applied is added to this.

  As described above, in the conventional example using the spring, it is necessary to lengthen or enlarge the spring in order to lower the spring constant, and as a result, the entire size of the probe portion increases. When the probe portion becomes large in this way, it is difficult to keep the temperature uniform, the shape measurement accuracy deteriorates, and the measurement axis for scanning the probe must be increased due to the increase in size, resulting in an increase in apparatus cost. .

  Further, if the pressing force is to be reduced, a weaker spring is required, so that the spring portion of the probe becomes very large, which is practically impossible with the conventional method.

  (2) The pressing force of the probe is likely to change. It is conceivable that the spring expands or contracts due to the influence of ambient temperature change or the like. In the conventional example, the force generated by the spring is large because it includes the weight of the probe. Therefore, if the generated force of the spring changes due to the expansion and contraction of the spring, the influence on the probe pressing force is great.

  For example, in the above-mentioned example, the force that the spring has is F = 9.8 × 10 + 0.1 = 98.1 mN. Accordingly, even a change of only 0.1% results in a change of 0.0981 mN, which is a very large error with respect to the probe pressing force of 0.1 mN. For this reason, precise shape measurement is difficult.

  (3) In the case of the conventional example using a magnetic circuit instead of such a spring, the weight cancellation part of a probe becomes large. That is, as disclosed in Patent Document 2, the method of canceling the weight of the probe using magnetic force is to fix the yoke so that the probe is sandwiched between the yoke, the permanent magnet and the magnetic circuit using the magnetic circuit. The dead weight is canceled by the magnetic force generated between the probes. Therefore, it is necessary to provide a magnetic circuit consisting of a yoke, permanent magnet, and coil around the probe. If the magnetic flux flowing through the magnetic circuit is disturbed, the force generated between the probe and the yoke changes, leading to measurement errors. End up. Therefore, a part made of a material that disturbs the magnetic flux, for example, an iron-based material, cannot be arranged around the probe. As a result, the weight cancellation portion of the probe becomes large. In addition, there are problems due to heat generated by the coil and unsolved problems that it is difficult to greatly change the pressing force of the probe only by controlling the energization of the coil.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and compensates the weight of the probe of the shape measuring device by a magnetic circuit composed of a box-shaped yoke and a permanent magnet. It is an object of the present invention to provide a contact probe and a shape measuring apparatus that can be downsized and can greatly improve measurement accuracy.

In order to achieve the above object, the contact type probe of the present invention scans a moving member that can be moved three-dimensionally by bringing a probe held so as to be displaceable in the direction of gravity into contact with the object to be measured. A contact probe for measuring a coordinate position, the probe comprising a tip sphere and a probe shaft, and a permanent magnet fixed to the probe shaft , surrounding the permanent magnet, and below the permanent magnet A box-shaped yoke made of a magnetic body having inner surfaces facing each other with a gap that increases in distance toward the distance , and the yoke is held by the moving member, and by the magnetic force generated by the permanent magnet and the magnetic flux flowing through the yoke, A force for canceling gravity applied to the probe and a force as a spring element that changes according to the displacement of the probe with respect to the yoke are generated. And wherein the door.

  A magnetic circuit consisting of a permanent magnet attached to the probe and a box-shaped yoke surrounding it, generates a force that cancels the weight of the probe and a force that acts as a spring element to press the probe against the object to be measured Therefore, by adjusting the inner surface shape and material of the permanent magnet or yoke, the spring constant can be reduced as much as when using a large spring, and the magnetic force of the permanent magnet and yoke can be used. Therefore, the measurement accuracy can be improved without being affected by dimensional changes caused by temperature changes as in the case of using a spring or coil. In addition, since the magnetic circuit is surrounded by a box-shaped yoke, this part also serves as a magnetic shield, and even if there is a magnetic substance such as iron around it, it is not affected, reducing the space required for the magnetic circuit it can.

  Thus, by further reducing the size of the contact probe using a magnetic circuit that does not require a large spring, the entire shape measuring apparatus can be reduced in size and simplified, and the manufacturing cost can be reduced.

  In addition, by making the inner surface of the yoke a curved surface with a constant curvature, the inner surface of the yoke can be easily processed with a lathe, which can contribute to cost reduction. In addition, since the processing accuracy of the yoke is improved, the self-weight compensation of the probe is further stabilized, and extremely precise shape measurement can be performed.

A probe that is a contact type probe shown in FIG. 1A has a probe tip 2 having a sphere 1 at the tip, a probe shaft 4 that supports the probe tip 2, and the like, and the measurement axis of the shape measuring apparatus shown in FIG. 15 is held via a guide G so as to be movable in the direction of gravity (Z direction) with respect to the housing 10 which is a moving member that moves integrally with the housing 15. At the upper end of the probe shaft 4, a permanent magnet 8 fitted and inserted into a box-shaped yoke 7 with a clearance δ as shown in FIG. Magnetic force acts between the permanent magnet 8 and the yoke 7 to attract each other, but the probe shaft 4 is guided by the guide G so as to be movable in the above-described direction of gravity (Z direction), and is generated in the clearance δ. Since the magnetic force generates a force in the direction in which the distance (distance) between the permanent magnet 8 and the yoke 7 is reduced, if the inner surface of the yoke 7 facing the permanent magnet 8 is, for example, cylindrical with a radius of curvature R, the probe is a guide. A force is also applied along G in the Z direction.

  The force that the probe receives in the moving direction can be adjusted by parameters such as the inner surface shape and material of the yoke, the shape and material of the permanent magnet, and the gap size between the yoke and the permanent magnet. For example, if a strong magnet is used, a strong force can be generated.

  Further, if the inner surface of the yoke has a shape in which a gap between the permanent magnet and the permanent magnet changes abruptly depending on the position of the probe, the force can be greatly changed depending on the position of the probe. For example, if the inner surface of the yoke is convex, a force can be generated so that the magnet moves toward the most protruding position. In this way, the magnetic force can be used to generate an offset force that cancels the weight of the probe and a spring element force that changes according to the displacement of the probe.

  FIG. 1E shows a contact probe according to a conventional example. A probe shaft 104 having a ball 101 at the tip is supported by a housing 110 having a guide G through a spring 103. While this spring 103 needs to be a very weak spring, it has to support the weight of the probe, and the extension of the spring 103 becomes very large, so that the entire probe becomes long.

  On the other hand, according to the present embodiment, since the magnetic force generated by the yoke 7 and the permanent magnet 8 is used, it is not necessary to use a large weak spring as in the conventional example, and a small probe can be realized. Further, since the spring is not deformed and the pressing force is not changed due to a temperature change or the like as in the conventional example, the stability of the pressing force is improved.

  Further, even if a member made of an iron-based material is disposed around the yoke 7, the magnetic circuit inside the yoke is a box-shaped yoke that is not affected, and the magnetic circuit inside the yoke is shielded against an external magnetic field. Therefore, the self-weight canceling part of the probe can be greatly reduced in size.

  As the guide for the probe shaft, an arbitrary one such as a rolling guide, a parallel leaf spring, or an air bearing can be used.

  Moreover, if the inner surface shape of the yoke 7 is a cylindrical surface having a certain curvature as described above, the inner surface of the yoke can be easily machined with a lathe or the like. Compared to the case where a complicated curved surface is used, the processing is simple and the processing accuracy is high, so that the manufacturing cost of the probe can be reduced and the precise load setting can be performed.

  Next, the operation of the magnetic circuit shown in FIGS. 1A and 1B will be described. This magnetic circuit can be schematically represented as shown in FIG. Here, let the residual magnetic flux density Br and the holding force Hc be constants of the permanent magnet 8, and let the magnetic flux flowing through the magnetic circuit be Φ. The magnetic resistance of the yoke portion is represented by Ry, the magnetic resistance Rc of the iron core portion, and the magnetic resistance between the permanent magnet 8 and the yoke 7 is represented by Rg.

  Further, as shown in FIG. 1D, the clearance δ between the permanent magnet 8 and the yoke 7 is expressed by a function X = A (z), the thickness of the permanent magnet 8 is lm, and the magnetic flux path is interrupted. When the area is S, the magnetic permeability of air is ua, and the magnetic permeability of iron is uf, the magnetic resistances Ry, Rc, Rg are

The magnetic flux density B flowing through the magnetic circuit is

The z-direction shear force (magnetic force) F can be calculated from the following equation.

となる。式（６）中のＡを From this and equation (4),

It becomes. A in formula (6)

と表されるＸＺ平面内で（Ｒ+δ、Ｚｕ）を中心とする半径Ｒの円の一部であるとする。

And a part of a circle with a radius R centered at (R + δ, Zu) in the XZ plane expressed as

here,
L: 40 [mm]
lm: 1.5 [mm]
lc: 9 [mm]
S: 7.068 [mm ^-2 ]
Br: 1.2 [T]
Hc: 900000 [A / m]
ua: 1.26e-9 [H / m]
uf: 8.82e-7 [H / m]
R: 100 [mm]
δ: 2 [mm]
Substituting this value into equation (6) and Taylor expansion to the first order around z = 0,
F = 0.06467-11.14z (however, F [N], Z [m]) (8)
It becomes.

  The first term in Equation (8) is a term that generates an offset force that supports the weight of the probe with a constant value. The second term includes the movement amount z of the probe, and indicates that the force decreases as z increases. Since the generated force changes as the probe is displaced, it is the force of the spring element corresponding to a mechanical spring.

From equation (6),

である。式（９）から永久磁石８とヨーク７のすきまδが広がる程、ずり力Ｆの値は大きくなることがわかる。

It is. It can be seen from equation (9) that the shear force F increases as the clearance δ between the permanent magnet 8 and the yoke 7 increases .

  As described above, the magnetic circuit shown in FIG. 1 also serves as a spring element in addition to a counter balance action by a constant force that supports the weight of the probe. In addition, the magnitude | size of the 1st term in Formula (8) and the inclination (gradient) of the 2nd term can be adjusted by changing a magnetic resistance, a coercive force, the cross-sectional area of a magnetic flux path, etc.

  2A shows a shape measuring apparatus incorporating the contact probe of FIG. 1. A probe tip 2 having a conical tip for attaching a sphere 1 has a probe shaft sandwiched by a spacer 3. 4 is fixed by screwing. Further, a mirror 6 is bonded and fixed on the holder 5 via a mirror fixing piece, and an iron core 9 having two permanent magnets 8 bonded to both ends is inserted into the hollow portion of the holder 5. Screwed to the upper side of the shaft 4.

  The probe shaft 4 is supported so as to be movable in the vertical direction with respect to the housing 10 via an air bearing 11 that is a guide that is supported in a non-contact manner through a thin air film. A compressed air hole 12 for guiding compressed air is drilled in the hole. These compressed air holes 12 can be freely drawn around the inside of the housing 10 by drilling from one side with a drill and closing the surface portion of the hole with screws or an adhesive as necessary. The compressed air hole 12 is connected to a compressed air pipe 13 and further connected to a compressed air source (not shown). With this configuration, the probe shaft 4 can freely move in the vertical direction without friction.

  The housing 10 is provided with a protruding lower stopper 10 b on the lower surface thereof, and restricts excessive movement of the probe shaft 4 in the upward direction by colliding with the spacer 3. Similarly, a projection-like upper stopper 10a is provided on the upper surface portion of the housing 10 so as to abut against the projection 4a provided on the probe shaft 4 for excessive downward movement. In order to reduce the impact, a damper such as a thin rubber sheet is bonded and fixed to these stoppers 10a and 10b. The housing 10 is fixed and supported by a second housing 16 fixed to the measurement shaft 15.

  The yoke 7 is fixed to the second housing 16 by a yoke connecting jig 17, and FIG. 2A shows the arrangement of the yoke 7, the permanent magnet 8, etc. when this part is viewed from below. A box-shaped yoke 7 surrounds a permanent magnet 8 and an iron core 9 fixed to the probe shaft 4 and constitutes a magnetic circuit shown in FIG. The inner surface of the yoke 7 facing the permanent magnet 8 is a curved surface having a constant radius of curvature R in the probe moving direction, as shown in FIG.

  The force generated by the magnetic circuit is based on the above-described equation (8), and also serves as a spring element in which the force changes in accordance with the displacement, in addition to a counterbalance effect that generates a force that supports the weight of the probe.

  The measurement shaft 15 is supported by an XY table 28 as scanning means so as to be movable in the same direction as the probe shaft 4, that is, in the vertical direction (Z direction), and is driven by a ball screw 36 and a servo motor 29. The The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation is performed as described later according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the mirror 26. A mounting table on which the object to be measured 24 is mounted is provided below the frame 25.

  A position sensor 23 as detection means is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor 29 is controlled so that the output of the sensor amplifier 14 is constant.

  Next, the measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

  First, the control system switching device 33 is set to the position control system. That is, the feedback control system is selected so that the position of the measurement axis 15 is constant, and the measurement axis 15 is retracted in the safe position, that is, the direction in which the probe is farthest from the object to be measured 24 (step S1).

  Then, the XY table 28 is moved so as to be on the first measurement point (step S2), the measurement shaft 15 is lowered, the probe and the object to be measured 24 are brought into contact, and the position sensor 23 is in a predetermined position. The measuring shaft 15 is lowered (step S3).

  Here, when the sphere 1 at the tip of the probe contacts the object to be measured 24 and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the above formula (8) increases to the plus side. Then, since the generated force of the magnetic circuit is weakened, the force with which the sphere 1 at the tip of the probe presses the object to be measured 24 gradually increases accordingly. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the probe pressing force.

  The contact between the probe tip sphere 1 and the object 24 to be measured can be determined by monitoring the probe displacement measurement signal, that is, the sensor amplifier 14 signal.

  Then, the control system changeover switch 33 is switched to the needle pressure control system to control the value of the position sensor 23 to be constant (step S4). As it is, the measurement area of the object to be measured 24 is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis 15 is measured by a coordinate position measuring means (not shown) (step S5). Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched again to the position control system, the measurement shaft 15 is retracted to the safe position (step S6), and the measurement is terminated.

  According to the present embodiment, the gravity applied to the probe tip sphere 1, probe tip 2, spacer 3, probe shaft 4, holder 5, mirror 6 and the like is canceled by the magnetic force generated by the magnetic circuit. There is no need to use large springs. As a result, a small probe can be realized.

  Regarding the magnetic flux leakage, since the permanent magnet is surrounded by a box-shaped yoke made of a ferromagnetic material, there is no restriction that it is not possible to place a ferrous material component in the vicinity of the magnetic circuit as in the prior art. Accordingly, it is possible to greatly reduce the weight canceling portion of the probe, which can further contribute to the miniaturization of the probe.

  Furthermore, since a spring or a coil that generates heat with respect to environmental changes such as temperature changes is not used, the accuracy of the pressing force of the probe is improved, and as a result, the measurement accuracy is improved.

  Further, since the cross-sectional shape of the inner surface of the yoke facing the permanent magnet is a circular shape with a constant curvature in the probe moving direction, the yoke can be easily designed and manufactured, and thus the manufacturing cost can be reduced.

  As shown in FIG. 4, in this embodiment, a box-shaped yoke 37 having a tapered opening 37a is used, and the magnitude of the pressing force of the probe by the magnetic circuit composed of the yoke 37 and the permanent magnet 8 is changed to the opening 37a. Yoke driving means for adjusting the taper by moving the yoke 37 in the taper direction is provided. With this configuration, even if the weight of the probe changes due to, for example, replacement of the probe ball 1 or the like, the force generated by the magnetic circuit can be freely adjusted to keep the probe pressing force constant.

  4A, as in FIG. 1A, the probe tip 2 having a conical tip for attaching the sphere 1 is screwed under the probe shaft 4 with the spacer 3 interposed therebetween. Fixed. A mirror 6 is bonded and fixed on the holder 5 via a mirror fixing piece, and an iron core 9 having two permanent magnets 8 bonded to both ends is inserted into the hollow portion of the holder 5, and the holder 5 is a probe shaft. 4 is fixed by screwing.

  The probe shaft 4 is supported so as to be movable in the vertical direction with respect to the housing 10 via an air bearing 11 that is a guide that is supported in a non-contact manner through a thin air film. A compressed air hole 12 for guiding compressed air is drilled in the hole. These compressed air holes 12 can be freely drawn around the inside of the housing 10 by drilling from one side with a drill and closing the surface portion of the hole with screws or an adhesive as necessary. The compressed air hole 12 is connected to a compressed air pipe 13 and further connected to a compressed air source (not shown). With this configuration, the probe shaft 4 can freely move in the vertical direction without friction.

  The housing 10 is provided with a protruding lower stopper 10 b on the lower surface thereof, and restricts excessive movement of the probe shaft 4 in the upward direction by colliding with the spacer 3. Similarly, a projection-like upper stopper 10a is provided on the upper surface portion of the housing 10 so as to abut against the projection 4a provided on the probe shaft 4 for excessive downward movement. The housing 10 is fixed and supported by a second housing 16 fixed to the measurement shaft 15.

  The yoke 37 is supported by the second housing 16 so as to be movable using the guide 21 in a direction orthogonal to the probe shaft 4, that is, in the front-rear direction (Y direction), and is a pinion rack serving as a yoke moving means. It is moved by the mechanism 40 and the servo motor 38. A servo motor 38 for driving the yoke 37 is supported by a servo motor jig 39 and connected to a servo amplifier 41. An encoder 38 a is connected to the rotation shaft of the servo motor 38, and its output is connected to the position control compensation circuit 42.

  FIG. 4B is a view of the arrangement of the yoke 37 and the permanent magnets 8 as viewed from above. The box-shaped yoke 37 has a tapered opening 37 a whose opening width α in the X direction changes in the Y direction, and constitutes a magnetic circuit together with the permanent magnet 8 and the iron core 9 fixed to the probe shaft 4. A constant curvature is provided on the inner surface of the yoke 37 facing the permanent magnet 8 in the probe moving direction.

  The force generated by the magnetic circuit configured as described above is changed according to the displacement in addition to the counter balance action that generates the offset force that supports the weight of the probe, as described above based on the equation (8). It also functions as a spring element.

  Further, as described above, the clearance between the permanent magnet 8 and the yoke 37 is changed by driving the servo motor 38 and displacing the yoke 37 in the Y direction perpendicular to the Z direction which is the probe moving direction. The force that supports the probe's own weight can be changed. By grasping in advance the relationship between the displacement of the yoke 37 in the Y direction perpendicular to the probe moving direction and the force that supports the probe's own weight, the pressing force at the time of measurement can be adjusted to an arbitrary value. Further, it is possible to correct the pressing force when the weight of the probe changes due to the replacement of the tip and the tip sphere.

  The measuring shaft 15 is supported by the XY table 28 so as to be movable in the direction along the probe shaft 4, that is, in the vertical direction (Z direction), and is driven by the ball screw 36 and the servo motor 29. . The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation is performed as described later according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the mirror 26. A mounting table on which the object to be measured 24 is mounted is provided below the frame 25.

  The position sensor 23 is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor is controlled so that the output of the sensor amplifier 14 becomes constant.

  Next, a measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

  First, the probe is fixed to the lower end (step S101). That is, by moving the yoke 37 in the Y direction in which the clearance between the permanent magnet 8 and the yoke 37 is widened, the magnetic force acting between the permanent magnet 8 and the yoke 37 is weakened, and the probe can be lowered. In this way, the protrusion 4a of the probe shaft 4 is brought into contact with the upper stopper 10a, and the probe is fixed to the lower end.

  When the probe is fixed to the lower end, the value z1 of the position sensor 23 is read and stored in a storage device (not shown) (step S102).

  Then, the yoke 37 is moved to a preset probe mass measurement position (step S103), the value z2 of the position sensor 23 when the probe is balanced is read, and the difference z3 (= z2−z1) between z2 and z1 is not shown. Stored by the storage device (step S104). z3 is a floating amount of the probe from the stopper 10a.

  Next, the probe mass is measured (step S105). That is, if the probe lift amount zd in the case where the probe mass is the reference mass m is known in advance, the probe tip sphere 1 can be replaced by multiplying the difference between zd and z3 by the spring coefficient in the probe moving direction. It is possible to calculate the mass m1 changed due to the above.

  For example, it is assumed that the lifting amount zd when the spring coefficient is 30 [mN / mm] and the reference mass m is 80 mN is 1 [mm]. At this time, if the measured lifting amount z3 is, for example, 0.95 mm, the changed mass m1 is m1 = (zd−z3) × 30 = 1.5 mN. That is, it can be seen that the probe is heavier than the reference mass m by 1.5 mN.

  If the calculated m1 does not exceed the allowable value Δm, it is considered that the ball has been exchanged normally, and the measurement operation is continued. If m1 exceeds Δm, it is determined that the ball exchange was not successful and the measurement is terminated.

  Thus, the preparation of the probe is completed, and the shape measurement process starts. First, the control system switching device 33 is set to the position control system, that is, the feedback control system is selected so that the position of the measurement shaft 15 is constant, and the safe position, that is, the probe is the most from the object to be measured 24. The measuring shaft 15 is retracted in the direction of leaving (step S106). Next, the probe is fixed to the lower end in the same manner as in step S101 (step S107). Then, the XY axis 28 is moved so as to be above the first measurement point, the measurement axis 15 is lowered, the probe and the object to be measured 24 are brought into contact, and the measurement axis 15 is moved until the position sensor 23 reaches a predetermined position. Lower (step S109).

  Here, when the ball 1 at the tip contacts the object to be measured 24 and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the above formula (8) increases to the plus side. Then, since the generated force of the magnetic circuit is weakened, the force with which the sphere 1 at the tip of the probe presses the object to be measured 24 gradually increases accordingly. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the pressing force of the probe.

  The contact between the probe tip sphere 1 and the object 24 to be measured can be determined by monitoring the probe displacement measurement signal, that is, the sensor amplifier 14 signal. Since the probe is in contact with the protrusion 4a of the probe shaft 4 and the protruding upper stopper 10a of the housing 10, the probe does not move even if the measurement shaft 15 moves and there is disturbance vibration. Therefore, the signal of the sensor amplifier 14 is not swayed by disturbance vibration, and contact determination can be easily performed. That is, since it is only necessary to monitor whether or not a predetermined signal level is reached, the presence or absence of contact can be determined at a very high speed, for example, 1 ms.

  Next, the yoke 37 is moved so that the pressing force becomes a set value (step S110). As described above, when the yoke 37 is moved in the Y direction orthogonal to the probe moving direction, the clearance between the permanent magnet 8 and the yoke 37 changes, and the force that supports the weight of the probe of the formula (8) changes. In advance, in the probe having the reference mass m, the relationship between the position y of the yoke 37 and the pressing force f is grasped as y = G (f), and the position of the yoke 37 corresponding to the set value of the pressing force is determined accordingly. The yoke 37 is moved. However, if the sphere 1 etc. at the tip of the probe is replaced, the probe mass shifts, and this is corrected using the probe mass deviation amount m1 obtained in step S105. That is, when the set value of the pressing force so far is f0, if the set value is corrected to f0-m1 and the yoke position y is obtained, the displacement amount of the probe mass is canceled and the pressing force is accurately determined. Can be set. For example, when f0 is 100 mg and m1 is 40 mg, if the pressing force is corrected to 100−40 = 60 mg and the yoke position y is obtained, the displacement amount of the probe mass due to ball exchange or the like can be corrected.

  Then, the control system changeover switch 33 is switched to the needle pressure control system to control the value of the position sensor 23 to be constant (step S111). As it is, the measurement area of the object to be measured 24 is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis 15 is measured by a coordinate position measuring means (not shown) (step S112). Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched again to the position control system, the measurement axis is retracted to the safe position (step S113), and the measurement is terminated.

  As described above, according to the present embodiment, gravity applied to the sphere 1 at the probe tip, the probe tip 2, the spacer 3, the probe shaft 4, the holder 5, and the mirror 6 is canceled by the magnetic force generated by the magnetic circuit. To do. Since it is not necessary to use a large spring as in the conventional example, a small probe can be realized.

  Furthermore, since a spring whose generated force changes with respect to environmental changes such as temperature changes is not used, the accuracy of the pressing force of the probe is improved, and as a result, the measurement accuracy is improved.

  Also, by moving the yoke that constitutes the magnetic circuit, it is possible to correct the change in probe mass caused by the exchange of the probe tip and sphere, etc., and the accuracy of the pressing force is improved. As a result, the shape measurement accuracy Will improve.

  In addition, there is a step of moving the yoke by the yoke moving means to bring the probe into contact with the upper stopper to make the origin, and a step of measuring the position where the weight of the probe and the magnetic force of the magnetic circuit are balanced by the position sensor. Therefore, the probe mass and the probe position can be managed with high accuracy, and the shape measurement accuracy can be greatly improved.

  FIG. 6 shows a shape measuring apparatus according to the third embodiment, which has a magnetic circuit including a yoke 7 and permanent magnets 8 as in the apparatus of FIG. 2, and moves the yoke 7 in the Z direction parallel to the probe moving direction. A yoke driving means for adjusting the generated force of the magnetic circuit is provided.

  As shown in FIGS. 6A and 6C, the yoke 7 includes a yoke moving guide 51 that moves in the vertical direction (Z direction) along the probe shaft 4 and a support member 52 that supports the yoke movably. Is held by a yoke moving body 55 which is a yoke driving means supported by the second housing 16 and is driven by a ball screw 56 by a servo motor 53. A servo motor 53 that moves up and down the yoke 7 is connected to a servo amplifier 41, an encoder 54 is connected to the rotating shaft of the servo motor 53, and its output is connected to a position control compensation circuit 42.

  FIG. 6B is a plan view of the arrangement of the yoke 7 and the permanent magnet 8 as seen from above. The yoke 7 has a box shape, and constitutes a magnetic circuit together with the permanent magnet 8 and the iron core 9 fixed to the probe shaft 4. The inner surface shape of the yoke 7 facing the permanent magnet 8 is a curved surface having a constant curvature in the probe moving direction.

  The force generated by the magnetic circuit configured as described above is changed according to the displacement in addition to the counter balance action that generates the offset force that supports the weight of the probe as described above based on the equation (8). It also functions as a spring element.

  Further, as described above, due to the displacement of the yoke 7 in the Z direction parallel to the moving direction of the probe, the clearance between the permanent magnet 8 and the yoke 7 changes, and the force that supports the probe's own weight changes. By grasping in advance the relationship between the displacement in the direction parallel to the probe movement direction of the yoke 7 at the measurement position and the force that supports the probe's own weight, the pressing force at the time of measurement can be made variable. Further, it is possible to correct the pressing force when the weight of the probe changes due to the replacement of the tip and the tip sphere.

  The measuring shaft 15 is supported by the XY table 28 so as to be movable in the direction along the probe shaft 4, that is, in the vertical direction (Z direction), and is driven by the ball screw 36 and the servo motor 29. . The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation is performed as described later according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the mirror 26. A mounting table (not shown) for an object to be measured is provided in a lower portion of the frame 25, and the object to be measured 24 is fixed to the mounting table.

  The position sensor 23 is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor is controlled so that the output of the sensor amplifier 14 becomes constant.

  Next, a measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

First, the probe is fixed to the lower end (step S101a). That is, by moving the yoke 7 in the Z direction where the clearance between the permanent magnet 8 and the yoke 7 becomes narrow , the magnetic force acting between the permanent magnet 8 and the yoke 7 is weakened, and the probe can be lowered. In this way, the protrusion 4a of the probe shaft 4 is brought into contact with the upper stopper 10a, and the probe is fixed to the lower end.

  When the probe is fixed to the lower end, the value z1 of the position sensor 23 is read and stored in a storage device (not shown) (step S102).

  Then, the yoke 7 is moved to a preset probe mass measurement position (step S103a), the value z2 of the position sensor 23 when the probe is balanced is read, and the difference z3 (= z2−z1) between z2 and z1 is not shown. Stored by the storage device (step S104). z3 is a floating amount of the probe from the stopper 10a.

  Next, the probe mass is measured (step S105). That is, if the probe lift amount zd in the case where the probe mass is the reference mass m is known in advance, the probe tip sphere 1 can be replaced by multiplying the difference between zd and z3 by the spring coefficient in the probe moving direction. It is possible to calculate the mass m1 changed due to the above.

  For example, it is assumed that the lifting amount zd when the spring coefficient is 30 [mN / mm] and the reference mass m is 80 mN is 1 [mm]. At this time, if the measured lifting amount z3 is, for example, 0.95 mm, the changed mass m1 is m1 = (zd−z3) × 30 = 1.5 mN. That is, it can be seen that the probe is heavier than the reference mass m by 1.5 mN.

  If the calculated m1 does not exceed the allowable value Δm, it is considered that the ball has been exchanged normally, and the measurement operation is continued. If m1 exceeds Δm, it is determined that the ball exchange was not successful and the measurement is terminated.

  Thus, the preparation of the probe is completed, and the shape measurement process starts. First, the control system switching device 33 is set to the position control system, that is, the feedback control system is selected so that the position of the measurement shaft 15 is constant, and the safe position, that is, the probe is the most from the object to be measured 24. The measuring shaft 15 is retracted in the direction of leaving (step S106). Next, the probe is fixed to the lower end in the same manner as in step S101a (step S107a). Then, the XY axis 28 is moved so as to be above the first measurement point, the measurement axis 15 is lowered, the probe and the object 24 are brought into contact, and the measurement axis is lowered until the position sensor 23 reaches a predetermined position. (Step S109).

  Here, when the ball 1 at the tip contacts the object to be measured 24 and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the above formula (8) increases to the plus side. Then, since the generated force of the magnetic circuit is weakened, the force with which the sphere 1 at the tip of the probe presses the object to be measured 24 gradually increases accordingly. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the pressing force of the probe.

  The contact between the probe tip sphere 1 and the object 24 to be measured can be determined by monitoring the probe displacement measurement signal, that is, the sensor amplifier 14 signal. Since the probe is in contact with the protrusion 4a of the probe shaft 4 and the protruding upper stopper 10a of the housing 10, the probe does not move even if the measurement shaft 15 moves and there is disturbance vibration. Therefore, the signal of the sensor amplifier 14 is not swayed by disturbance vibration, and contact determination can be easily performed. That is, since it is only necessary to monitor whether or not a predetermined signal level is reached, the presence or absence of contact can be determined at a very high speed, for example, 1 ms.

  Next, the yoke 7 is moved so that the pressing force becomes a set value (step S110a). As described above, when the yoke 7 is moved in the probe moving direction, the clearance between the permanent magnet 8 and the yoke 7 changes, and the constant force that supports the weight of the probe of the formula (8) changes. In advance, in the probe of the reference mass m, the relationship between the position y of the yoke 7 and the pressing force f is grasped as y = G (f), and the position of the yoke 7 corresponding to the set value of the pressing force is determined accordingly. The yoke 7 is moved. However, if the sphere 1 etc. at the tip of the probe is replaced, the probe mass will shift. This is corrected using the probe mass deviation m1 obtained in step S105. That is, when the setting value of the pressing force is f0, the setting value is corrected to f0-m1 and the yoke position y is obtained, so that the displacement amount of the probe mass is canceled and the pressing force is accurately set. be able to. For example, when f0 is 100 mg and m1 is 40 mg, if the pressing force is corrected to 100−40 = 60 mg and the yoke position y is obtained, the displacement amount of the probe mass due to ball exchange or the like can be corrected.

  Then, the control system changeover switch 33 is switched to the needle pressure control system to control the value of the position sensor 23 to be constant (step S111). As it is, the measurement area of the DUT 24 is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis 15 is measured by a coordinate measuring device (not shown) (step S112). Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched to the position control system again, the measurement axis is retracted to the safe position (step S113), and the measurement is terminated.

  Since other points are the same as those of the second embodiment, description thereof is omitted.

  In this embodiment, as shown in FIG. 8, the probe is lowered against the magnetic force of the magnetic circuit by the yoke 7 and the permanent magnet 8, etc., and the current for bringing the protrusion 4a of the probe shaft 4 into contact with the upper stopper 10a. A probe driving means comprising a control device 71, a permanent magnet 72, and a coil 73 is provided, and the displacement history of the probe can be reset to remove the hysteresis of the generated force of the magnetic circuit by the yoke 7 and the permanent magnet 8. It is configured to be able to. As a result, the pressing force of the probe can be stabilized and more accurate shape measurement can be performed.

  Since the permanent magnet 8 and the yoke 7 have hysteresis in their magnetic characteristics, there is hysteresis between the displacement and the generated force even when the magnetic force is used as a spring element. That is, even if the probe displacement is the same, the generated force varies depending on the displacement history of the probe so far. When the generated force changes in this way, the probe is suspended by the spring element, so the position where the probe is waiting changes. Even in that case, if the pressing force during measurement is always made constant, the probe constant during measurement changes because the spring constant is constant. The change in probe position at the time of measurement means that the three-dimensional position and orientation of the probe also change, leading to a measurement error. Moreover, since it changes due to an uncertain probe displacement history, a measurement error that changes every time is generated. Conversely, if the probe position at the time of measurement is always made constant, the spring constant is constant, and the pressing force at the time of measurement changes. The change in the pressing force at the time of measurement means that the deformation amount of the object to be measured 24 or the probe changes, which leads to a measurement error. Moreover, since it changes due to an uncertain probe displacement history, a measurement error that changes every time is generated. Therefore, in order to remove the hysteresis of the force generated by the magnetic circuit of the yoke 7 and the permanent magnet 8, a magnetic means comprising a permanent magnet 72 and a coil 73 for generating a Lorentz force is provided.

  In FIG. 8A, the probe tip 2 having a conical tip for attaching the sphere 1 is screwed and fixed to the lower side of the probe shaft 4 with the spacer 3 interposed therebetween as in FIG. To do. A mirror 6 is bonded and fixed on the holder 5 via a mirror fixing piece, and an iron core 9 having two permanent magnets 8 bonded to both ends is inserted into the hollow portion of the holder 5, and the holder 5 is a probe shaft. 4 is fixed by screwing.

  The probe shaft 4 is supported so as to be movable in the vertical direction with respect to the housing 10 via a so-called air bearing 11 that supports the probe shaft 4 in a non-contact manner through a thin air film. A compressed air hole 12 is formed to guide the compressed air. These compressed air holes 12 can be freely drawn around the inside of the housing 10 by drilling from one side with a drill and closing the surface portion of the hole with screws or an adhesive as necessary. The compressed air hole 12 is connected to a compressed air pipe 13 and further connected to a compressed air source (not shown). With this configuration, the probe shaft 4 can freely move in the vertical direction without friction.

  The housing 10 is provided with a protruding lower stopper 10 b on the lower surface thereof, and restricts excessive movement of the probe shaft 4 in the upward direction by colliding with the spacer 3. Similarly, a projection-like upper stopper 10a is provided on the upper surface portion of the housing 10 so as to abut against the projection 4a provided on the probe shaft 4 for excessive downward movement. The housing 10 is fixed and supported by a second housing 16 fixed to the measurement shaft 15.

  The probe shaft 4 is provided with a permanent magnet 72, and the housing 10 is provided with a coil 73. The coil 73 is connected to the current control device 71, and can generate a Lorentz force that drives the probe shaft 4 in the Z direction by energizing the coil 73.

  The yoke 7 is fixed to the second housing 16 via a yoke connecting jig 17. FIG. 8B shows the arrangement of the yoke 7 and the permanent magnet 8 from below. The yoke 7 has a box shape, and constitutes a magnetic circuit together with the permanent magnet 8 and the iron core 9 fixed to the probe shaft 4. A constant curvature is provided on the inner surface of the yoke 7 facing the permanent magnet 8 in the probe moving direction.

  The generated force of the magnetic circuit configured as described above is not limited to the counterbalance function that generates a constant offset force that supports the weight of the probe, as described based on the above-described equation (8). It also functions as a changing spring element.

  The measurement shaft 15 is supported by the XY table 28 so as to be movable in the vertical direction (Z direction) along the probe shaft 4 using a guide 31, and is driven by a ball screw 36 and a servo motor 29. The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation described later is performed according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the reference mirror 26. A mounting table on which the object to be measured 24 is mounted is provided below the frame 25.

  The position sensor 23 is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor is controlled so that the output of the sensor amplifier 14 becomes constant.

  Next, a measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

  First, the probe is fixed to the lower end by the probe driving means (step S201). That is, the current controller 71 energizes the coil 73 and applies a negative Z force to the probe. As a result, the probe shaft 4 moves downward, the protrusion 4a of the probe shaft 4 contacts the upper stopper 10a, and the probe is fixed to the lower end.

  Next, the control system switching device 33 is set to the position control system, that is, the feedback control system is selected so that the position of the measurement shaft 15 is constant, and the safe position, that is, the probe is the object to be measured 24 most. The measuring shaft 15 is retracted in the direction away from the center (step S202).

  Then, the XY axis 28 is moved so as to be above the first measurement point (step S203), the measurement axis 15 is lowered, the probe and the object 24 are brought into contact, and the position sensor 23 is in a predetermined position. The measuring shaft 15 is lowered (step S204).

  Here, when the ball 1 at the tip contacts the object to be measured 24 and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the above formula (8) increases to the plus side. Then, since the force generated by the magnetic circuit is weakened, the force with which the sphere 1 at the tip of the probe presses the object to be measured 24 gradually increases accordingly. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the pressing force of the probe.

  The contact between the probe tip sphere 1 and the object 24 to be measured can be determined by monitoring the probe displacement measurement signal, that is, the sensor amplifier 14 signal. Since the probe is in contact with the protrusion 4a of the probe shaft 4 and the protruding upper stopper 10a of the housing 10, the probe does not move even if the measurement shaft 15 moves and there is disturbance vibration. Therefore, the signal of the sensor amplifier 14 is not swayed by disturbance vibration, and contact determination can be easily performed. That is, since it is only necessary to monitor whether or not a predetermined signal level is reached, the presence or absence of contact can be determined at a very high speed, for example, 1 ms.

  Next, the probe is freed (step S205). That is, the current controller 71 stops energization of the coil 73, and the probe moves freely.

  Then, the control system switching device 33 is switched to the needle pressure control system, and control is performed so that the value of the position sensor 23 becomes constant (step S206). As it is, the measurement area of the object to be measured 24 is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis 15 is measured by a coordinate position measuring means (not shown) (step S207). Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched to the position control system again, the measurement axis 15 is retracted to the safe position (step S208), and the measurement is terminated.

  As described above, according to this embodiment, the gravity applied to the probe tip sphere 1, probe tip 2, spacer 3, probe shaft 4, holder 5, mirror 6, etc. Cancel by the magnetic force generated. Therefore, it is not necessary to use a large spring as in the conventional example. For this reason, a small probe is realizable.

  Furthermore, since a spring whose generated force changes with respect to environmental changes such as temperature changes is not used, the accuracy of the pressing force of the probe is improved, and as a result, the shape measurement accuracy is improved.

  In addition, by energizing the coil 73 before bringing the probe into contact with the object to be measured 24, a force that lowers the probe shaft 4 works, and the protrusion 4a can be brought into contact with the stopper 10a. Thereby, since the displacement history of the probe is reset, there is no hysteresis of the force generated by the magnetic circuit composed of the yoke 7, the permanent magnet 8, and the iron core 9, and the accuracy of the pressing force of the probe is improved. As a result, the shape measurement accuracy is improved.

FIG. 10 is a schematic diagram for explaining the relationship between the probe displacement and the generated force of the magnetic circuit. The horizontal axis is the relative displacement between the probe and the housing 10, and the vertical axis is the generated force of the magnetic circuit. Since the magnetic circuit acts as a spring element as described above, the generated force changes when the relative displacement between the probe and the housing 10 changes. Here, with an ideal spring element, when the displacement is initially Z ₁ and the generated force is P ₀ , the generated force when the displacement once changes to Z ₂ and then becomes Z ₁ again is the first. When similarly becomes a P _0, since the hysteresis between the forces magnetic circuit generates the displacement by the magnetic properties of the permanent magnet 8 generated force is present, also generated force to return the displacement Z ₀ and P ₀ Don't be. That is, the generated force in the case of the displacement history of Z ₁ → Z ₂ → Z ₁ → Z ₀ → Z ₁ changes as P ₀ → P ₁ → P ₂ → P ₃ → P ₄ . Since the probe is structured to be supported by the housing 10 by the spring element of the magnetic circuit, the displacement history is indeterminate considering that vibration is always generated, and the generated force is indeterminate as the displacement history. There is a problem that the pressing force cannot be set accurately because it depends on the object.

Therefore, the housing 10 is provided with stoppers 10a and 10b that limit the movement range in the probe moving direction, and is fixed to the housing 10 and provided with a coil 73, and fixed to the probe shaft 4 with a permanent magnet 72, and flows through the coil 73. A current control device 71 for controlling the current is provided. By passing a current through the coil 73, the probe shaft 4 comes into contact with the stopper 10a and cancels the displacement history. That is, in FIG. 10, if P ₅ , P ₆ , and P ₀ are set as start points, the probe displacement is returned to Z ₁ after the probe displacement is set to Z ₂ , the generated force is always P ₃ .

  Thus, once the probe is brought into contact with the stopper 10a, the hysteresis of the magnetic circuit is eliminated and the pressing force can be set with high accuracy.

  FIG. 11 shows a shape measuring apparatus according to the fifth embodiment for lowering the probe against the magnetic force of the magnetic circuit by the yoke 7 and the permanent magnet 8, etc., so that the protrusion 4a of the probe shaft 4 contacts the upper stopper 10a. The probe displacement history is reset by the probe driving means comprising the nozzle 81, the air valve 82, and the pipe 83. By providing a step of fixing the probe to the stopper 10a, the hysteresis of the generated force is removed, the pressing force is stabilized, and precise shape measurement can be performed.

  In FIG. 11A, as in FIG. 2A, the probe tip 2 having a conical tip for attaching the sphere 1 is screwed into the lower side of the probe shaft 4 with the spacer 3 interposed therebetween. Fix it. A mirror 6 is bonded and fixed on the holder 5 via a mirror fixing piece, and an iron core 9 having two permanent magnets 8 bonded to both ends is inserted into the hollow portion of the holder 5. The holder 5 is connected to the probe shaft 4. It is fixed to the upper side of the screw.

  The probe shaft 4 is supported so as to be movable in the vertical direction with respect to the housing 10 via a so-called air bearing 11 that supports the probe shaft 4 in a non-contact manner through a thin air film. A compressed air hole 12 is formed to guide the compressed air. These compressed air holes 12 can be freely drawn around the inside of the housing 10 by drilling from one side with a drill and closing the surface portion of the hole with screws or an adhesive as necessary. The compressed air hole 12 is connected to a compressed air pipe 13 and further connected to a compressed air source (not shown). With this configuration, the probe shaft 4 can freely move in the vertical direction without friction.

  The housing 10 is provided with a protruding lower stopper 10 b on the lower surface thereof, and restricts excessive movement of the probe shaft 4 in the upward direction by colliding with the spacer 3. Similarly, a projection-like upper stopper 10a is provided on the upper surface portion of the housing 10 so as to abut against the projection 4a provided on the probe shaft 4 for excessive downward movement. The housing 10 is fixed and supported by a second housing 16 fixed to the measurement shaft 15.

  The second housing 16 is provided with a nozzle 81 that blows air in a direction to push down the probe, and a pipe 83 connected to the nozzle 81 is connected to a compressed air source (not shown) through an air valve 82. Therefore, by opening the air valve 82, compressed air is blown out from the nozzle 81, the probe is moved downward, and the stopper 10a and the protrusion 4a of the probe shaft 4 can be brought into contact with each other.

  The yoke 7 is fixed to the second housing 16 via a yoke connecting jig 17. FIG. 11B is a plan view of the arrangement of the yoke 7 and the permanent magnet 8 as seen from below. The yoke 7 has a box shape, and constitutes a magnetic circuit together with the permanent magnet 8 and the iron core 9 fixed to the probe shaft 4. A constant curvature is provided on the inner surface of the yoke 7 facing the permanent magnet 8 in the probe moving direction.

  The force generated by the magnetic circuit configured as described above is based on the displacement according to the displacement in addition to the counterbalance action that generates a constant offset force that supports the weight of the probe, as described above based on the equation (8). It also functions as a spring element that changes.

  The measurement shaft 15 is supported by the XY table 28 so as to be movable in the vertical direction (Z direction) along the probe shaft 4 using a guide 31, and is driven by a ball screw 36 and a servo motor 29. The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation described later is performed according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the mirror 26. A mounting table on which the object to be measured 24 is mounted is provided below the frame 25.

  The position sensor 23 is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor is controlled so that the output of the sensor amplifier 14 becomes constant.

  Next, a measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

  First, the probe is fixed to the lower end (step S201a). That is, the air valve 82 is opened, compressed air is blown out from the nozzle 81, the probe is moved downward, and the stopper 10a and the protrusion 4a of the probe shaft 4 are brought into contact with each other.

  Next, the control system switching device 33 is set to the position control system, that is, the feedback control system is selected so that the position of the measurement shaft 15 is constant, and the safe position, that is, the probe is the object to be measured 24 most. The measuring shaft 15 is retracted in the direction away from the center (step S202).

  Then, the XY axis 28 is moved so as to be above the first measurement point (step S203), the measurement axis 15 is lowered, the probe and the work are brought into contact, and the measurement axis is moved until the position sensor 23 reaches a predetermined position. Reduce (step S204).

  Here, when the sphere 1 at the tip of the probe contacts the object to be measured 24 and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the above formula (8) increases to the plus side. Then, since the force generated by the magnetic circuit is weakened, the force with which the sphere 1 at the tip of the probe presses the object to be measured 24 gradually increases accordingly. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the pressing force of the probe.

  The contact between the probe tip sphere 1 and the object 24 to be measured can be determined by monitoring the probe displacement measurement signal, that is, the sensor amplifier 14 signal. Since the probe is in contact with the protrusion 4a of the probe shaft 4 and the protrusion-like stopper 10a of the housing 10, the probe does not move even if the measurement shaft 15 moves and there is disturbance vibration. Therefore, the signal of the sensor amplifier 14 is not swayed by disturbance vibration, and contact determination can be easily performed. That is, since it is only necessary to monitor whether or not a predetermined signal level is reached, the presence or absence of contact can be determined at a very high speed, for example, 1 ms.

  Next, the probe is freed (step S205a). That is, the air valve 82 is closed to stop the supply of compressed air to the nozzle 81, thereby freeing the probe movement.

  Then, the control system switching device 33 is switched to the needle pressure control system, and control is performed so that the value of the position sensor 23 becomes constant (step S206). As it is, the measurement area of the object to be measured 24 is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis is measured by a coordinate position measuring means (not shown) (step S207). Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched to the position control system again, the measurement axis 15 is retracted to the safe position (step S208), and the measurement is terminated.

  As described above, according to the present embodiment, the gravity applied to the probe tip sphere 1, probe tip 2, spacer 3, probe shaft 4, holder 5, mirror 6, etc. is canceled by the magnetic force generated by the magnetic circuit. . Therefore, it is not necessary to use a large spring as in the conventional example. For this reason, a small probe is realizable.

  Furthermore, since a spring whose generated force changes with respect to environmental changes such as temperature changes is not used, the accuracy of the pressing force of the probe is improved, and as a result, the shape measurement accuracy is improved.

  Further, before the probe is brought into contact with the object to be measured 24, the air valve 82 is opened and the compressed air is blown out from the nozzle 81, so that the force for lowering the probe shaft 4 works and the protrusion 4a is brought into contact with the stopper 10a. Can do. Thereby, since the displacement history of the probe is reset, the hysteresis of the force generated by the magnetic circuit composed of the yoke 7, the permanent magnet 8, and the iron core 9 is eliminated, and the accuracy of the pressing force is improved. As a result, the shape measurement accuracy is improved.

1 shows an embodiment, (a) is a schematic diagram showing a relationship between a probe, a yoke and a permanent magnet, (b) is a plan view showing only the yoke and the permanent magnet, (c) is a yoke and the permanent magnet, FIG. 6D is a partial cross-sectional view showing a positional relationship between a yoke and a permanent magnet, and FIG. 5E is a view explaining a contact type probe according to a conventional example. The shape measuring apparatus by Example 1 is shown, (a) is a schematic cross section which shows the principal part, (b) is the top view which looked at the yoke and the permanent magnet from the bottom, (c) is C of (b) It is sectional drawing taken along the -C line. 3 is a flowchart illustrating a shape measurement process according to the first embodiment. The shape measuring apparatus by Example 2 is shown, (a) is a schematic cross section which shows the principal part, (b) is a top view which shows arrangement | positioning of a yoke and a permanent magnet, (c) is C of (b). It is sectional drawing taken along the -C line. 10 is a flowchart illustrating a shape measurement process according to a second embodiment. The shape measuring apparatus by Example 3 is shown, (a) is a schematic cross section which shows the principal part, (b) is a top view which shows arrangement | positioning of a yoke and a permanent magnet, (c) is C of (b). It is sectional drawing taken along the -C line. 10 is a flowchart illustrating a shape measurement process according to a third embodiment. The shape measuring apparatus by Example 4 is shown, (a) is a schematic cross section which shows the principal part, (b) is a top view which shows arrangement | positioning of a yoke and a permanent magnet, (c) is C of (b). It is sectional drawing taken along the -C line. 10 is a flowchart showing a shape measurement process according to Example 4; It is a graph explaining the hysteresis of the magnetic circuit by a yoke and a permanent magnet. The shape measuring apparatus by Example 5 is shown, (a) is a schematic cross section which shows the principal part, (b) is a top view which shows arrangement | positioning of a yoke and a permanent magnet, (c) is C of (b). It is sectional drawing taken along the -C line. 10 is a flowchart illustrating a shape measurement process according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sphere 2 Probe tip 3 Spacer 4 Probe shaft 4a Protrusion 5 Holder 6 Mirror 7, 37 Yoke 8, 72 Permanent magnet 9 Iron core 10, 16 Housing 10 a, 10 b Stopper 11 Air bearing 12 Compressed air hole 13 Compressed pipe 14 Position sensor amplifier 15 Measurement axis 21, 51 Yoke movement guide 22 Yoke guide connecting member 23 Position sensor 24 Object 25 Frame 26 Reference mirror 27 Interferometer 28 XY axis 29 Motor 30 Encoder 31 Guide 32 Motor amplifier 33 Control system switching device 34 Needle pressure control compensation Circuit 35 Position control compensation circuit 36, 56 Ball screw 38, 53 Servo motor 39 Servo motor jig 40 Pinion rack mechanism 41 Servo amplifier 42 Position control compensation circuit 54 Encoder 55 Yoke moving body 71 Current control device 73 Coil 81 Nozzle 82 Air valve 83 Piping

Claims (9)

A contact-type probe that measures a coordinate position by scanning a movable member that is movable in three dimensions with a probe held in a gravitational direction in contact with an object to be measured.
The probe consists of a tip sphere and a probe shaft,
A permanent magnet fixed to the probe shaft;
A box-shaped yoke made of a magnetic body having an inner surface facing the permanent magnet and having a gap that increases in distance downward from the permanent magnet;
The yoke is held by the moving member, and a force that cancels gravity applied to the probe by a magnetic force generated by the magnetic flux flowing through the permanent magnet and the yoke, and a spring element that changes according to the displacement of the probe with respect to the yoke A contact-type probe that generates force. A contact-type probe that measures a coordinate position by scanning a movable member that is movable in three dimensions with a probe held in a gravitational direction in contact with an object to be measured.
The probe consists of a tip sphere and a probe shaft,
A permanent magnet fixed to the probe shaft;
A box shape made of a magnetic body that surrounds the permanent magnet and has an inner surface facing the gap with a gap that increases in a downward direction between the permanent magnet and changes in a direction perpendicular to the direction of gravity. A yoke driving means for moving the yoke in a direction perpendicular to the direction of gravity with respect to the probe,
The yoke is held by the moving member via the yoke driving means, and the force that cancels the gravity applied to the probe by the magnetic force generated by the magnetic flux flowing through the permanent magnet and the yoke, and the displacement of the probe with respect to the yoke A contact probe characterized by generating a force as a spring element that changes according to the above. A contact-type probe that measures a coordinate position by scanning a movable member that is movable in three dimensions with a probe held in a gravitational direction in contact with an object to be measured.
The probe consists of a tip sphere and a probe shaft,
A permanent magnet fixed to the probe shaft;
A box-shaped yoke made of a magnetic material that surrounds the permanent magnet and has an inner surface facing the permanent magnet with a gap that increases in distance downward .
Yoke driving means for moving the yoke in the direction of gravity with respect to the probe;
The yoke is held by the moving member via the yoke driving means, and the force that cancels the gravity applied to the probe by the magnetic force generated by the magnetic flux flowing through the permanent magnet and the yoke, and the displacement of the probe with respect to the yoke A contact probe characterized by generating a force as a spring element that changes according to the above.   The contact probe according to any one of claims 1 to 3, wherein the box-shaped yoke has a curved inner surface curved with a constant curvature in the direction of gravity.   The detection means which detects the relative position of a probe and a moving member is provided, The mass of the said probe is calculated based on the output of the said detection means, The Claim 1 thru | or 4 characterized by the above-mentioned. Contact probe. The moving member has a stopper that restricts the movement of the probe in the direction of gravity, and is provided with probe driving means for moving the probe in the direction of gravity and coming into contact with the stopper. Item 6. The contact probe according to any one of Items 1 to 5 . The contact probe according to claim 6 , wherein the probe driving means includes magnetic means for generating a Lorentz force on the probe. 7. The contact probe according to claim 6 , wherein the probe driving means is configured to move the probe by blowing or sucking air. A contact probe of claims 1 to 8 to any one of claims, and scanning means for scanning said contact probe on the test object measurement, the coordinate position measuring means for measuring the three-dimensional coordinate position of the probe A shape measuring apparatus characterized by comprising.

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