Polar coordinate drive device

Abstract

To provide production means for performing machining (or measurement) that requires high roundness guarantee, capable of easily coping with mixed loading of different kinds of work-pieces and fluctuations in production quantity.SOLUTION: A table surface of a machining center is provided with: an orthogonal stage 1 movable freely in XY directions but constrained in rotation around a Z axis; and a polar coordinate drive mechanism composed of a θ axis that rotates around the Z axis, and an R-axis that determines a distance in a normal direction provided on the θ axis. Furthermore, an R-axis movable part and the orthogonal stage are rotatably connected. Thereby, driving the θ-axis causes the orthogonal stage to perform precession movement with an eccentricity quantity determined by the R-axis as a revolution radius.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polar coordinate drive device that drives a Cartesian stage in polar coordinates. [Background technology]

[0002] Traditionally, NC automatic lathes have been used for mass-produced products that require highly accurate circular machining. This allows for a fast cycle time by automatically processing and separating the finished product from the bar stock as it feeds the bar stock. However, there are problems with this method, such as the need for a long space for the bar stock feed mechanism and the time required to change the setting.

[0003] Therefore, for small-lot production, NC lathes were used to load and unload workpieces one by one into a chuck, but this was significantly less productive than NC automatic lathes. On the other hand, machining centers, which process a large number of workpieces fixed on a pallet, are able to easily accommodate fluctuations in quantity. Summary of the Invention [Problem to be solved by the invention]

[0004] However, when it comes to workpieces that require high-precision arcs or circles, it is difficult to guarantee accuracy when machining on a machining center because the roundness depends on the interpolation accuracy of the X and Y axes, so only the relevant parts are machined on an NC lathe, which increases the cost of machining, the number of workers required, and the cost of equipment. Therefore, an object of the present invention is to provide a production device for performing processing (or measurement) that requires a high degree of roundness assurance, and which can easily accommodate the mixing of different types of workpieces and fluctuations in production quantity. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides a polar coordinate drive device characterized by a polar coordinate positioning mechanism having at least two degrees of freedom, X and Y, but no rotational degree of freedom around the Z axis, which is rotatably coupled to the polar coordinate positioning mechanism having at least two degrees of freedom, Rθ, around the Z axis. In other words, the object is to provide a polar coordinate drive device characterized by connecting a polar coordinate positioning mechanism that is rotatable around the Z axis, the polar coordinate positioning mechanism being composed of an orthogonal stage that can move freely on the XY plane but is restricted from rotating around the Z axis perpendicular to the XY plane, a θ axis having a rotation plane parallel to the XY plane, and an R axis that determines the distance in the normal direction from the center of rotation of the θ axis. [Effects of the Invention]

[0006] With this configuration, the Cartesian stage 1 performs precession without tilting, and its revolution speed is determined only by the θ-axis speed, the revolution radius is determined only by the R-axis position, and the revolution trajectory accuracy is determined only by the guidance accuracy of the θ-axis guide mechanism, making it easy to confirm reproducibility and, ultimately, to guarantee processing accuracy.

[0007] For example, even if machining is divided between a machining center and an NC lathe because it includes parts that require a high degree of roundness, automatic machining can be performed with a single machine by installing this polar coordinate drive device on the table surface of the machining center to create a multi-tasking machine.In other words, movement of parts that require a high degree of roundness to a reference position and other machining feeds and positioning can be performed by driving the X and Y axes of the machining center, and round machining can be performed by driving the polar coordinate drive device of the present invention. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of a polar coordinate driving device according to a first embodiment. [Figure 2] 2 is an explanatory diagram of the main parts of the R axis and the θ axis in FIG. 1 and the position of the workpiece relative to the tool. [Figure 3] FIG. 10 is an explanatory diagram of a polar coordinate driving device according to a second embodiment. [Figure 4] FIG. 10 is an explanatory diagram of a polar coordinate driving device according to a third embodiment. [Figure 5] FIG. 10 is an explanatory diagram of a polar coordinate driving device according to a fourth embodiment. [Figure 6] FIG. 1 is an explanatory diagram of workpieces and machining tools arranged on a pallet. DETAILED DESCRIPTION OF THE INVENTION

[0009] Representative examples of the present invention are illustrated by the following examples and drawings. [Example]

[0010] Fig. 1 is an explanatory diagram of a polar coordinate drive device according to a first embodiment, and Fig. 2 is an explanatory diagram of the main parts of the R-axis and θ-axis in Fig. 1 and the position of the workpiece relative to the tool. The right-hand diagram (b) in Fig. 2 shows the outer ring of the small diameter bearing 40 in (a) rotated 180°. 2 shows the configuration of the concentrically arranged large diameter bearing 10 which is the θ-axis guide, the small diameter bearing 40 which is the R-axis output end, and the large diameter eccentric shaft 20 and small diameter eccentric shaft 30 which fill the gap between them. The axis of the large diameter bearing 10 is indicated by a, the axis of the small diameter bearing 40 by b, the sliding surfaces where the large diameter eccentric shaft 20 and the small diameter eccentric shaft 30 fit together are indicated by 25a, and the axis of 25a is indicated by c.

[0011] The large diameter bearing 10 and the small diameter bearing 40 are each configured as a pair of back-to-back preload bearings in which the internal clearance is eliminated by adjusting the difference width. The large diameter eccentric shaft has an inner diameter sliding surface eccentric by ΔY relative to its outer diameter, and the small diameter eccentric shaft has an outer diameter sliding surface eccentric by ΔY relative to its inner diameter.

[0012] In Figure (a), the eccentric directions of the large-diameter eccentric shaft 20 and the small-diameter eccentric shaft 30 are in opposite phases, resulting in the large-diameter bearing 10 and the small-diameter bearing 40 being concentric. In Figure (b), the eccentric directions are in the same phase, resulting in the amount of eccentricity of the axis of the small-diameter bearing 40 relative to the axis of the large-diameter bearing 10 being twice ΔY.

[0013] The outer diameter surface of the large diameter eccentric shaft 20 is fitted and fixed to the inner ring of the large diameter bearing 10, and the inner diameter surface of the small diameter eccentric shaft 30 is fitted and fixed to the outer ring of the small diameter bearing 40. Furthermore, the sliding contact surface 25a between the large diameter eccentric shaft 20 and the small diameter eccentric shaft 30 constitutes a sliding bearing, and in addition, a rolling guide is also used by numerous spheres 25b in a V-groove to suppress the upper limit of friction.

[0014] The outer ring of the large diameter bearing 10, which is a main part configured as described above, is mounted on a base 9 and fastened to a table surface 91 of the machining center. The large diameter eccentric shaft 20 extends downward and is connected to the rotor of a θ-axis motor 23, and the stator of the θ-axis motor 23 is connected to the base 9 by a channel member 8.

[0015] 2(a)-2(b), the R-axis motor controls the eccentricity of the axis of the small-diameter bearing 40 relative to the axis of the large-diameter bearing 10. The lower end of a connecting pin 41 is fitted into the inner ring of the small-diameter bearing 40 and is rotatably supported, and the upper end is fixed to the orthogonal stage 1 with a fastener 42.

[0016] In other words, the R axis, which is made up of the large diameter eccentric shaft 20 and its internal parts, is mounted on the rotating part of the θ axis, which is made up of the large diameter bearing 10 and the θ axis motor 23 . Furthermore, the orthogonal stage 1 is fastened to a base 9 via orthogonal guides 2 and 3. Reference numerals 90 and 92 denote the Y-axis base and Y-axis linear guide of the machining center. A workpiece 4 to be machined is fixed to the orthogonal stage 1 by a fixture (not shown), and a machining tool 5 accesses the workpiece from above the orthogonal stage 1.

[0017] Next, we will explain the operation when machining the inner diameter surface of the workpiece 4 of this embodiment with the machining tool 5. In the figure, it is assumed that the workpiece is the outer ring of a rolling bearing, and its raceway surface is to be machined with high circularity. First, the R-axis motor (not shown) drives the worm wheel 24 to set the bearing arrangement as shown in Figure 2(a), then the XY axes of the machining center are used to align the center of the workpiece 4 with the center of the spindle (not shown), and the Z-axis (not shown) of the machining center is lowered to align the machining tool 5 to the machining height.

[0018] After starting the spindle, the θ-axis motor 23 is started to rotate the inner ring of the large-diameter bearing 10, and then the small-diameter eccentric shaft 30 is rotated by the R-axis motor to move from the state in Figure 2(a) to the state in Figure 2(b). As a result, the orthogonal stage 1 and workpiece 4 move to the left and simultaneously begin precession with the eccentricity determined by the R-axis as the orbital radius, causing interference with the machining tool, and the interfering portion is removed by the rotation of the machining tool 5 by the spindle.

[0019] When the cutting allowance reaches the specified amount ΔR, the revolution radius is fixed by stopping the R axis, and the cutting process to achieve roundness that matches the rotational accuracy of the large diameter bearing that is the θ axis guide is completed. After that, the R axis is reversed to return to the state shown in Figure 2(a), and then the Z axis of the machining center is raised to move the cutting tool 5 away from the workpiece, completing the process. This machining does not use the XY axes of the machining center for machining feed; instead, only the R axis performs the cutting operation and only the θ axis performs the feed operation, achieving high-precision circularity machining comparable to that of a lathe while retaining the functionality of a machining center. [Example]

[0020] FIG. 3 is an explanatory diagram of a polar coordinate driving device according to a second embodiment, and the differences from the first embodiment will be explained. In this example, the R-axis 26 is mounted on top of the θ-axis motor 23. The lower end of a connecting pin 41 is fixed to the slider, which is the movable part of the R-axis, by a fastener 42. The upper end of the connecting pin 41 is fixed to the orthogonal stage by a bearing 40 so as to be freely rotatable. One end of the operating range of the R-axis slider is set at a position where the center of the connecting pin 41 roughly coincides with the center of rotation of the θ-axis, and the other end is set so that the distance between the center of the connecting pin 41 and the center of rotation of the θ-axis is ΔX.

[0021] The operation of this embodiment is the same as in embodiment 1, in that the orbital radius of the precession is determined by the position of the R-axis slider, and the precession is driven by the θ-axis motor 23. Unlike embodiment 1, the bearing that guides the θ-axis is built into the motor and does not interfere with the axial direction of the R-axis, making it easy to lengthen the stroke of the R-axis, making it suitable for machining and measuring outer diameter surfaces. The radius of precession in machining the inner diameter surface is the radius of the workpiece minus the tool radius, The radius of revolution of the precession during machining of the outer diameter surface is the sum of the radius of the workpiece to be machined and the radius of the tool, so a large radius of revolution is required. [Example]

[0022] Figure 4 is an explanatory diagram of Example 3 of a polar coordinate drive device. The difference from Example 1 is that Example 1 uses a worm and wheel for the R-axis drive mechanism, whereas this example uses spur gears 35 and 36. Since the R-axis is responsible for the infeed operation in high-roundness machining, it is most important that it does not move when stopped. Also, since the θ-axis is responsible for the feed operation in high-roundness machining, high-speed operation is not necessary. Therefore, this is an example in which ultrasonic motors are used for the R-axis and θ-axis motors. [Example]

[0023] FIG. 5 is an explanatory diagram of a fourth embodiment of the polar coordinate drive device. To further reduce the size of the third embodiment, an ultrasonic motor 28 is incorporated into the eccentric shaft to form the R-axis. Specifically, an ultrasonic linear motor as disclosed in Japanese Utility Model Laid-Open Publication No. 2-136487 is incorporated into the space provided in the large-diameter eccentric shaft 20, and a ball plunger 29 is pressed and fixed against the sliding surface 25a of the small-diameter eccentric shaft 30. The elliptical vibration of the legs excited by the two piezoelectric elements 28a drives the sliding surface of the small-diameter eccentric shaft 30 in the circumferential direction. Since the process that determines the accuracy of the present invention is when the R-axis is not driven, the ultrasonic motor's characteristic of providing a braking force due to friction when not driven is advantageous.

[0024] However, ultrasonic motors are not limited to this type, and other methods such as the inchworm method, which directly utilizes the expansion and contraction of piezoelectric or magnetostrictive elements (Micromechatronics Journal, Horological Society of Japan Vol. 62, No. 218), are also possible. In general production equipment, the process of bringing an end effector such as a tool or measuring probe close to the workpiece is very slow, so this mechanism, which is unable to move at high speeds, is actually an added value.

[0025] Although the above description is based on an embodiment, the present invention is not limited to this. For example, the polar coordinate drive mechanism may use hydraulic pressure, or manual screw adjustment is also possible. The guide for the rotating and linear moving parts may be air or oil hydrostatic guides or magnetic force. Furthermore, as shown in Figure 6, by loading a pallet with a large number of workpieces onto this device and installing it in a machining center, workpiece processing including high roundness processes can be performed in a manner that makes it easy to respond to fluctuations in quantity. [Industrial Applicability]

[0026] It can be widely used as a drive unit for production equipment that forms highly accurate roundness. Specifically, in mechanical processing applications, adding the drive unit of the present invention to a machining center adds functionality equivalent to that of a lathe. In laser thin plate processing machines, it enables faster arc cutting of parts, and is also suitable for direct electron beam or laser writing in the production of MEMS devices. Furthermore, adding the drive unit of the present invention to the workpiece mounting table of a three-dimensional measuring machine can add a roundness meter. [Explanation of symbols]

[0027] 1 Orthogonal stage 2,3 Orthogonal guide 10 Large diameter bearing (θ axis guide) 40 Small diameter bearing (R shaft output end)

Claims

1. A polar coordinate drive device characterized by the fact that a polar coordinate positioning mechanism is composed of an orthogonal stage that can move freely on the XY plane but is restricted in rotation around the Z axis perpendicular to the XY plane, a θ axis having a rotation plane parallel to the XY plane, and an R axis that determines the distance in the normal direction from the center of rotation of the θ axis, and the polar coordinate positioning mechanism is connected so that it can rotate freely around the Z axis.

2. A polar coordinate drive device characterized in that the R axis is driven by contact pressure using a piezoelectric element.

Images