Lifting drive device and measuring machine using the same

Abstract

Lifting drive device (11) of a lifting element (12) which is guided by a guide element (22) by means of an air layer, the lifting drive device comprising: a linear element (18) extending upwardly from the lifting element (12) and having an upper end held by the guide element (22); a compensating device (19) for reducing an apparent weight of the lifting element (12) suspended by the linear element (18); at least one roller (15) with which the guide element (22) is provided and which is in contact with the lifting element (12); and a rotary drive part (17) for rotating the roller (15), characterized in that the linear element (18) is a wire having a diameter of 0.3 mm to 3 mm, and the compensating device (19) is arranged to amplify a tension acting on the wire, the guide element (22) comprises a plurality of air cushions (24) which are arranged such that they face each other and surround the lifting element (12) from an X direction and a Y direction and in two stages with a distance in a lifting direction Z, and wherein the roller (15) is arranged between the two stages in the stroke direction Z.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a movement mechanism of a measuring head used in a measuring machine. BACKGROUND OF THE INVENTION

[0002] A measuring machine that has a probe attached to a measuring head and performs various measurements by bringing the probe close to a work from any direction often includes a lifting drive device for the measuring head. Probes such as a contact / non-contact probe, a high-resolution camera, and the like are selectively attached to the measuring head in accordance with various measurements, and a position (coordinate), image, shape, and the like of a work are measured with high accuracy using respective probes. Furthermore, measurements are sometimes performed using an illuminator attached to the measuring head to illuminate a part of a work to be measured using the illuminator.

[0003] Patent Literature 1 discloses a Z-direction drive mechanism, which is a stroke drive device for a conventional measuring head. As described in Fig. 5, this Z-direction drive mechanism includes a Z-axis spindle 12 having a probe 13 at a lower end and held vertically, a guide tube 22 for guiding the Z-axis spindle 12 in a vertical direction, a support shaft 28 extending upward from the inside of the Z-axis spindle 12, a pair of rollers 15, 16 with which the Z-axis spindle 12 is provided and between which a support shaft 28 is inserted, and a drive motor 17 for rotating the roller 15.

[0004] The guide tube 22 is supported by an X-sliding member 9 of an X-direction drive mechanism and moves in the X direction. The Z-axis spindle 12 is inserted into the guide tube 22, and a plurality of air cushions 24 for a plurality of air bearings are arranged in a space between the Z-axis spindle 12 and the guide tube 22. The air cushion 24 is arranged in the inner peripheral region of the guide tube 22 and forms an air bearing by expelling air to reduce frictional resistance between the guide tube 22 and the Z-axis spindle 12. Furthermore, a post 25 standing vertically upright is provided for the guide tube 22, and a horizontal support 26 provided at an upper end of this post 25 supports the upper end of the support shaft 28.

[0005] A piston is connected to a lower end of the support shaft 28, which is inserted into the interior of the Z-axis spindle 12, and a cylinder for accommodating this piston is provided in the Z-axis spindle 12. By supplying air into a cylinder chamber, a floating force acts on the cylinder. This floating force becomes a push-up force corresponding to the weight of the Z-axis spindle 12, thus reducing the apparent weight of the Z-axis spindle 12. Such a mechanism is referred to herein as an air balance mechanism.

[0006] To drive the Z-direction drive mechanism of Patent Literature 1, a motor 17 is driven to drive a drive roller 15. A support shaft 28 is inserted between the drive roller 15 and a driven roller 16, so that the rollers 15, 16 rise while rotating due to the frictional force between the rollers 15, 16 and the support shaft 28. Accordingly, the Z-axis spindle 12 moves up and down, and the probe 13 can be adjusted to a desired height. [PRIOR ART LITERATURE]PATENT LITERATURE

[0007] PATENT LITERATURE 1: JP 3 988 860 B2 DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0008] In measuring machines such as a coordinate measuring machine, performance that enables the measuring head holding the probe to be moved and positioned with high accuracy and speed in any direction of the X, Y, and Z axes is important, and maintaining such performance for a long period of time is also required. Therefore, in the linear motion drive devices for measuring heads, performance in terms of linear movement and high-speed operation of the Z-axis spindle is important. Although an air bearing, an air balance mechanism, and a friction drive mechanism in which a holding shaft is sandwiched between a pair of rollers are adopted for the Z-direction drive mechanism of Patent Literature 1 to exhibit such performance, suitability for structural simplification, weight reduction, and vibration countermeasures is also required.

[0009] For example, the Z-direction drive mechanism of Patent Literature 1 includes a pair of rollers between which a support shaft extending in a vertical direction is sandwiched. It moves the Z-axis spindle along the support shaft through the driving force of the rollers. To generate a predetermined amount of friction between the rollers and the support shaft, a contact area between the support shaft and each roller had to be ensured, and a support shaft with a very large cross-section was used. Therefore, the size reduction of the support shaft was limited.

[0010] Furthermore, as a countermeasure against the Z-axis spindle vibrating even slightly when the measuring head is moved in different directions, the Z-direction drive mechanism of Patent Literature 1 includes a thrust bearing provided at an upper end of the support shaft on which the Z-axis spindle is suspended, to actively dampen vibrations of the Z-axis spindle in many cases. However, providing the thrust bearing at the upper end of the support shaft is necessary as a countermeasure against vibrations, but it complicates the structure of the Z-direction drive mechanism.

[0011] The object of the present invention is to provide a lifting drive device for a measuring head that can achieve highly accurate linear movement and fast lifting of a lifting element (Z-axis spindle) guided by an air bearing, and is suitable for structural simplification, weight reduction, and vibration countermeasures. MEANS TO SOLVE THE PROBLEM

[0012] In order to achieve the above-mentioned object, a lifting drive device according to the present invention is a lifting drive device of a lifting member guided by a guide member by means of an air layer, and comprises: a linear member extending upwardly from the lifting member and having an upper end supported by the guide member; a balancing device for amplifying a tension acting on the linear member to reduce an apparent weight of the lifting member suspended by means of the linear member; at least one roller with which the guide element is provided and which is in contact with the lifting element; and a rotary drive part for rotating the roller.

[0013] According to this configuration, the balancer of the lifting drive device increases tension of the linear member by which the lifting member is suspended, and pulls the lifting member upward with the increased tension, so that the apparent weight of the lifting member can be reduced. Specific examples of the balancer include an air balancer mechanism using an air cylinder, a mechanism using a winch to wind the wire that is the linear member, and the like. The dead weight of the lifting member is canceled by the balancer, and the driving force required to lift the lifting member becomes small, making the configuration advantageous for high-speed lifting.Furthermore, the lifting drive device of the present invention forms an air layer between the lifting element and the guide element, and guides the lifting element up and down using the so-called air bearing. Since a friction section between the lifting element and the guide element is eliminated, a highly accurate linear movement of the lifting element can be maintained over a long period of time.

[0014] Furthermore, the lifting drive device of the present invention includes a roller in direct contact with the surface of the lifting member, which lifts the lifting member using its frictional force. This is not a conventional friction drive mechanism for a suspension member, but a friction drive mechanism for the lifting member. As a result, the linear member for suspending the lifting member can be slimmed down to the minimum required slenderness, and a linear member having flexibility has become selectable. It was necessary to provide a thrust bearing at an upper end of a support shaft for a relatively large rigid suspension member such as the conventional support shaft, however, the thrust bearing can be omitted when a linear member flexible in terms of bending and twisting, such as the present invention, is used as the suspension member.Examples of the linear element include a wire, a piano wire, a rope, a thin rod, and the like. In particular, the linear element is preferably a flexible wire or a thin rod.

[0015] On the other hand, in a configuration in which the linear element is selected as the suspension element of the lifting element merely to eliminate the thrust bearing at the upper end, the natural frequency of the lifting element becomes low, and the lifting element is easily vibrated compared to conventional configurations. In contrast, in the lifting drive device of the present invention, the linear element and at least one roller are simultaneously selected, which directly frictionally drives the lifting element. The roller is in contact with the lifting element at all times, so the natural frequency of the lifting element is not lowered, and its vibration can be suppressed. Even if vibration is generated, the vibration can be easily damped because contact with the roller is maintained.

[0016] Preferably, the at least one roller is provided in a pair and arranged such that the lifting element is interposed therebetween. To generate a frictional force between the lifting element and the roller, a force is required to press the drive roller against the lifting element. However, in the lifting drive device of the present invention, the lifting element is guided by the air bearing, so that a pushing-back force on the drive roller can be obtained by adjusting the air pressure of the air bearing. To securely generate a stable pushing-back force, the lifting element is preferably interposed between a pair of rollers.

[0017] Furthermore, the compensation scheme preferably includes: a piston connected to a lower end of the linear element and located in the lifting element; and a cylinder provided with the lifting member, for accommodating the piston therein, and moving up and down relative to the piston by means of air supplied to a cylinder chamber divided by the piston.

[0018] According to such a design, the piston and cylinder generate a push-up force equal to the weight of the lifting element by supplying air to the cylinder chamber divided by the piston. This is a so-called air balance mechanism using air cylinders. This air balance mechanism has a simple design, is easy to handle, and is suitable for weight reduction.

[0019] The measuring machine according to the present invention comprises a moving mechanism for moving a probe, the measuring machine having the lifting drive device and the probe mounted on the lifting member for measuring at least one of a position, an image and a shape of an object to be measured.

[0020] According to the lifting drive device of the present invention and the measuring machine comprising the same, the lifting member guided by the air bearing can be linearly moved with high accuracy to achieve a fast lifting movement, and those suitable for structural simplification, weight reduction, and vibration countermeasures can be provided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an external appearance of the measuring machine according to a first embodiment of the present invention. Fig. 2 is a partial sectional view showing the internal structure of the Z-axis moving device of the first embodiment. Fig. 3 schematically shows a direct friction drive mechanism of the first embodiment. Fig. Figure 4 shows schematically a modified example of the direct friction drive mechanism. Fig. Figure 5 shows a structure of the Z-direction drive mechanism for conventional measuring heads. BEST WAY TO CARRY OUT THE INVENTION

[0021] Hereinafter, embodiments of a Z-axis moving device which is a stroke driving device and a measuring machine using the same according to the present invention will be described with reference to figures.

[0022] Fig. 1 shows a three-dimensional measuring machine according to the present embodiment. This three-dimensional measuring machine 1 includes a base 2 for placing an object to be measured and a moving mechanism for moving a probe 13. As this moving mechanism, the three-dimensional measuring machine 1 includes a Y-axis moving device 3 for moving the probe 13 in the Y direction, an X-axis moving device 7 for moving the probe 13 in the X direction, and a Z-axis moving device 11 of the present embodiment for moving the probe 13 in the Z direction.

[0023] The base 2 is quadrangular, columnar, and includes a precisely flattened top for placing the object to be measured. Two directions that perpendicularly intersect each other on the top of the base 2 are referred to as the X direction and the Y direction, respectively, and the direction vertical to the top of the base 2 is referred to as the Z direction for the sake of explanation. The Y-axis moving device 3 includes a Y guide rail 4 provided on the base 2 in the Y direction, a left-side part 5L of a Y slide member provided to be movable along the Y guide rail 4, and a right-side part 6R of the Y slide member that moves on the base 2 in the Y direction in pairs with the left-side part 5L of the Y slide member. Air bearings are provided between the Y-guide rail 4 and the left-hand part 5L of the Y-sliding element and between the base 2 and the right-hand part 6R of the Y-sliding element.

[0024] The X-axis moving device 7 includes an X-beam 8, which is a longitudinally extending guide member whose two ends are supported by the left-side portion 5L and the right-side portion 6R of the Y-sliding member, an X-sliding member 9, which is a movable member provided to be movable along the longitudinal direction of the X-beam 8, and an X-sliding member driving part 10 for moving the X-sliding member 9. The X-beam 8 is a long beam-shaped member, and its two ends are supported over the left-side portion 5L and the right-side portion 6R of the Y-sliding member. When the Y-direction moving mechanism (Y-axis moving device 3) is pushed in the Y direction, the X-beam 8 is also moved in the Y direction. The X-sliding element 9 is designed to be movable along the X-beam 8. An air bearing is provided between the X-sliding element 9 and the X-beam 8.

[0025] Fig. Figure 2 shows the internal structure of the Z-axis moving device 11. The Z-axis moving device 11 includes a guide tube 22 as a guide member supported by the X-slider 9, and a Z-axis spindle 12 inserted in a vertical direction (Z direction) relative to the guide tube 22 as a lifting member. The central axis of the guide tube 22 is provided along the Z axis. Specific configurations of the Z-axis moving device 11 for each function will be explained below. <luftlager>

[0026] The guide surface in the guide tube 22 is formed by an air jet surface of a plurality of air cushions 24 arranged to surround the Z-axis spindle 12 from all directions (see Fig. 3). Compressed air from the air cushions 24 is expelled toward the Z-axis spindle 12, thereby forming an air layer between the Z-axis spindle 12 and the air cushions 24. The air cushions 24 are arranged facing each other and surround the Z-axis spindle 12 from the X and Y directions, respectively, and in two stages with a gap in the Z direction. Such a configuration of the air bearing makes it possible to maintain the non-contact state of the Z-axis spindle with respect to the guide tube 22. <luft-ausgleichsmechanismus>

[0027] Three posts 25 project above the guide tube 22 and support a horizontal support 26 located thereabove. The horizontal support 26 supports an upper end of a wire 18, and the Z-axis spindle 12 is suspended from the wire 18. The diameter of the wire is preferably from about 0.3 mm to about 10 mm, and more preferably from about 0.5 mm to about 3 mm. A wire having a diameter of about 1 mm is used in the present embodiment. The Z-axis spindle 12 is hollow, and a cylinder 20 is mounted therein. The central axis of the wire 18 and the center of the cylindrical part of the cylinder 20 lie approximately on a straight line. The lower end of the wire 18 is coupled to the piston 29 within the cylinder 20. An insertion opening for the wire 18 is provided in the top of the cylinder 20, and airtightness within the cylinder 20 is maintained by a sealing member 30.

[0028] The air balance mechanism 19 having such a configuration causes the cylinder 20 to levitate when compressed air is supplied to a pressure chamber inside the cylinder 20. This levitate acts in a direction that cancels the dead weight of the Z-axis spindle 12, so that a spindle drive mechanism, described below, can lift the Z-axis spindle 12 using a small driving force.

[0029] The air bearing and air balance mechanism have sections common to conventional designs. However, the present embodiment differs significantly from conventional designs in that the member for suspending the Z-axis spindle 12 has been changed from conventional support shafts to a wire. <Mechanismus für direkten Reibantrieb>

[0030] A direct friction drive mechanism 14 is adopted as a spindle drive mechanism in the present embodiment. Fig. Figure 2 shows the partially disassembled mechanism. The drive roller 15 is arranged such that it is in contact with the surface of the Z-axis spindle 12, as viewed from the Y direction. The drive roller 15 and its drive motor 17 are held by the guide tube 22 by means of a mounting element 32.

[0031] The drive roller 15 is designed to press against the surface of the Z-axis spindle 12 with a desired pressing force. Accordingly, the mounting member 32 includes a holding member 34 that holds the drive roller 15 and the motor 17, and a Y-direction guide member 36 provided on the guide tube 22 so that the holding member 34 is slightly displaced in the Y direction by the guide member 36. Furthermore, an elastic member 38 such as a spring is interposed between the holding member 34 and the guide member 36 so that the holding member 34 is biased in the Y direction. Consequently, the drive roller 15 presses against the surface of the Z-axis spindle 12 with the set pressing force. The power of the motor 17 is transmitted to the rotational axis of the drive roller 15 through the transmission belt to rotate the drive roller 15.

[0032] As shown schematically in Fig. As shown in Figure 3, the Z-axis spindle 12 receives further pressing force from the driven roller 16 provided on the side opposite to the drive roller 15. The pressing direction by the driven roller 16 is opposite to the pressing direction by the drive roller 15. By balancing the pressing forces of the pair of rollers 15, 16 between which the spindle 12 is sandwiched and generating the frictional force between the rollers 15, 16 and the surface of the spindle 12 caused by driving the drive roller 15, the Z-axis spindle 12 can be moved up and down. For example, the spring length of each roller 15, 16 and / or the air pressure of each air cushion 24 can be finely adjusted to balance the sum of the pressure force A of the drive roller 15 and the air pressure forces B on the upper and lower sides, as well as the sum of the pressure force A' of the driven roller 16 and the pressure forces C of the opposing air cushions 24.

[0033] In the modified example of the Fig. In the direct friction drive mechanism shown in Figure 4, the driven roller may not be provided, and only the air cushions 24 on the opposite side of the drive roller 15 may be arranged around the Z-axis spindle. In this case, the spring length of the roller 15 and / or the air pressure of each air cushion 24 can be finely adjusted to balance the sum of the activating force A of the drive roller 15 and the air pressure forces B on the upper and lower sides, as well as the sum of the pressure forces C of the opposite air cushions 24.

[0034] Now, effects of the Z-axis moving device 11 and the three-dimensional measuring machine incorporating the same of the present embodiment will be described. (1) The air bearing eliminates the abrasion between the Z-axis spindle 12 and the guide tube 22, allowing highly accurate linear movement of the guide tube 22 to be maintained for a long period of time. Furthermore, since the air balance mechanism 19 is incorporated therein, the driving force required for lifting is reduced by an amount equal to the weight of the Z-axis spindle 12 being offset. Consequently, stable linear movement and rapid positioning can be maintained. (2) As the spindle drive mechanism, the drive roller 15 is selected to move the spindle up and down by causing a friction force to act directly on the Z-axis spindle 12.

[0035] As an effect of this, first, a limitation on the size of the support member for the Z-axis spindle 12 is eliminated, so that the flexible wire 18, which has a relatively small cross-section, could be selected instead of a conventional rod with a very large cross-section. Furthermore, with conventional rods, it was necessary to provide a thrust bearing at the upper end of the rod. This is because conventionally, when the Z-axis spindle 12 is displaced in the X, Y directions, the upper end of the hollow rod had to be displaceable accordingly, otherwise vibrations generated in the Z-axis spindle 12 would be transmitted to the fixed side (the guide tube 22) and effects of the vibration would spread. However, by selecting the wire 18 as in the present invention, displacement of the Z-axis spindle 12 in the X, Y directions is absorbed by the flexibility of the wire 18.Therefore, the upper end of the wire 18 can be held using a simple method. The thrust bearing is no longer required, and the number of components can be reduced accordingly.

[0036] Next, the Z-axis spindle 12 on the moving side does not hold the roller 15 and the drive motor 17, but the guide tube 22 on the fixed side (ie, the X-slider side) holds the roller 15 and the drive motor 17. Therefore, the weight of the Z-axis spindle 12 can be reduced.

[0037] Furthermore, a disadvantage when only the wire 18 is selected is that the natural frequency of the Z-axis spindle 12 is lowered (generally: easily vibrated). If the wire is selected as a coupling element 18 of the Z-axis spindle 12 on the moving side with the guide tube 22 on the fixed side, a rigidity of the Z-axis spindle 12 is lowered, and the Z-axis spindle 12 is easily vibrated in all directions, X, Y, Z, compared to conventional rods. Moreover, in conventional rods, the upper end of the rod is supported by the thrust bearing, so vibrations of the Z-axis spindle in the X and Y directions were damped by the thrust bearing. If the wire 18 is selected merely to allow the thrust bearing to be omitted, the damping characteristics of such a Z-axis spindle 12 are deteriorated.However, in the present invention, the drive roller 15 is selected for direct frictional drive of the Z-axis spindle 12 together with the wire 18, so that the drive roller 15 is kept in contact with the Z-axis spindle 12 at all times. Accordingly, generation of vibrations is suppressed, and a vibration-damping effect is also expected.

[0038] A rod with a smaller diameter (about 3 mm in diameter) than conventional rods can be chosen as an alternative to the wire. In this case, the thrust bearing at the upper end of the rod is not required due to elastic deformation of the small-diameter rod. Furthermore, effects similar to those mentioned above (1) and (2) can be achieved. INDUSTRIAL APPLICABILITY

[0039] In addition to coordinate measuring machines, the present invention can be preferably used as other measuring machines such as an image measuring machine and a shape measuring machine, as well as vertical axis moving devices in optical devices such as microscope measuring machines. DESCRIPTION OF REFERENCE SYMBOLS 1 Three-dimensional measuring machine (measuring machine) 11 Z-axis movement device (lifting drive device) 12 Z-axis spindle (lifting element) 13 probe 14 Direct friction drive mechanism 15 Drive roller (roller) 16 Driven roller 17 Motor (rotary drive part) 18 wire (linear element) 19 Air balancing mechanism (balancing device) 20 cylinders 22 Guide tube (guide element) 24 air cushions for air bearings 29 pistons < / luftlager>

Claims

[1] Lifting drive device (11) of a lifting element (12) guided by a guide element (22) by means of an air layer, the lifting drive device comprising: a linear element (18) extending upwardly from the lifting element (12) and having an upper end held by the guide element (22); a compensating device (19) for reducing an apparent weight of the lifting element (12) suspended by the linear element (18); at least one roller (15) with which the guide element (22) is provided and which is in contact with the lifting element (12); and a rotary drive part (17) for rotating the roller (15), characterized by , that the linear element (18) is a wire having a diameter of 0.3 mm to 3 mm, and the compensating device (19) is arranged to amplify a tension acting on the wire, the guide element (22) comprises a plurality of air cushions (24) which are arranged such that they face each other and surround the lifting element (12) from an X direction and a Y direction and in two stages with a distance in a lifting direction Z, and wherein the roller (15) is arranged between the two stages in the stroke direction Z. [2] Lifting drive device (11) according to claim 1, wherein the at least one roller (15) is present in a pair and is arranged such that the lifting element (12) is inserted therebetween. [3] Lifting drive device (11) according to claim 1 or 2, wherein the compensating device (19) comprises: a piston (29) connected to a lower end of the linear element (18) and located in the lifting element (12); and a cylinder (20) provided with the lifting member (12) for accommodating the piston (29) therein, and moving up and down relative to the piston (29) by means of air supplied to a cylinder chamber divided by the piston (29). [4] A measuring machine (1) comprising a moving mechanism for moving a probe (13), the measuring machine comprising the lifting drive device (11) according to any one of claims 1 to 3, and the probe (13) is mounted on the lifting member (12) for measuring at least one of a position, an image and a shape of an object to be measured.

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