Method for controlling rotation speed in centrifugal barrel polishing and centrifugal barrel polishing method

Abstract

The present invention is to reduce chipping occurring in a workpiece during acceleration of a barrel tank. The method for controlling a rotation speed includes an acceleration control step of: calculating a constant Ct based on a number Nt (rpm) of revolutions per minute during polishing, a number nt (rpm) of rotations per minute during polishing, a revolution radius R (m) of the barrel tank (12), and gravitational acceleration g (9.8 m / s2) by using the expression (1): Ct=2πNt / 602·R / g·nt defining a relative centrifugal acceleration F(G) based on a number N (rpm) of revolutions per minute of the barrel tank (12) during acceleration control, the revolution radius R (m) of the barrel tank (12), and gravitational acceleration g (9.8 m / s2) by using the expression (2): F = (2πN / 60)2 • R / g ··· (2); and changing over time the number N (rpm) of revolutions per minute of the barrel tank (12) during the acceleration control and a number n (rpm) of rotations per minute of the barrel tank (12) during the acceleration control so as to satisfy the expression (3): F / n ≥ Ct ··· (3).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for controlling a rotation speed in centrifugal barrel polishing and a centrifugal barrel polishing method.BACKGROUND ART

[0002] Patent Literature 1 discloses a centrifugal barrel polishing apparatus including a rotary table that is rotationally driven by a drive motor and a barrel tank attached to an eccentric position of the rotary table. The barrel tank revolves integrally with the rotary table and rotates relative to the rotary table, thereby rotating in a planetary manner. In the barrel tank rotating in a planetary manner, a workpiece is polished by polishing stones.CITATIONS LISTPATENT LITERATURE

[0003] Patent Literature 1: JP 2010-005712ASUMMARY OF INVENTIONTECHNICAL PROBLEMS

[0004] In the centrifugal barrel polishing, in a case where a centrifugal force acting on the barrel tank is weak with respect to a number of rotations of the barrel tank, chipping, that is, an abnormal breakage, occurs in the workpiece. Therefore, during barrel polishing, a number of revolutions (orbital rotation speed) and a number of rotations (spin rotation speed) are set to the speed in consideration of reducing chipping. However, in a technical level in the related art, reduction of occurrence of chipping has not been considered with respect to an acceleration step from a polishing stop state until the barrel tank reaches the polishing rotation speed suitable for reducing chipping. Therefore, in the barrel polishing apparatus described in the Patent Literature 1, rotation of the rotary table and rotation of the barrel tank are performed by only one drive motor, and, during an acceleration step from a rotation stop state until the number of revolutions of the rotary table and the number of rotations of the barrel tank reach the target rotation speed suitable for polishing, the number of rotations increases at the same rate as the number of revolutions. Since the centrifugal force is proportional to the square of the number of revolutions, during the acceleration step, a state in which the centrifugal force is relatively small with respect to the number of rotations continues, so that there is a concern that chipping may occur in the workpiece. Once the acceleration is completed and the target rotation speed suitable for polishing is reached, the process transitions directly to a barrel polishing step in which the target rotation speed is maintained, and thus, it has also been difficult to verify a state of chipping of the workpiece during the acceleration step.

[0005] The present invention has been completed based on the circumstances described above, and an object of the present invention is to reduce chipping occurring in a workpiece during acceleration of a barrel tank.SOLUTIONS TO PROBLEMS

[0006] According to a first disclosure, there is provided a method for controlling a rotation speed in centrifugal barrel polishing, in which polishing is performed by rotating a barrel tank, into which a workpiece is input, in a planetary manner at a predetermined number of revolutions during polishing and a predetermined number of rotations during polishing, the method accelerating and controlling the rotation speed of the barrel tank from a rotation stop state until the rotation speed reaches the number of revolutions during polishing and the number of rotations during polishing, the method including an acceleration control step of: calculating a constant Ct based on the number Nt (rpm) of revolutions per minute during polishing, the number nt (rpm) of rotations per minute during polishing, a revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s 2< ) by using the following expression (1): C t = (2πN t / 60) 2< • R / (g•nt) ····· (1); defining a relative centrifugal acceleration F(G) based on a number N (rpm) of revolutions per minute of the barrel tank during acceleration control, the revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s 2< ) by using the following expression (2) : F = 2 πN / 60 2 · R / g and changing over time the number N (rpm) of revolutions per minute of the barrel tank during the acceleration control and a number n (rpm) of rotations per minute of the barrel tank during the acceleration control so as to satisfy the following expression (3): F / n ≥ C t

[0007] According to a second disclosure, there is provided a centrifugal barrel polishing method including: the acceleration control step according to the first disclosure, in which a revolution direction and a rotation direction of the barrel tank are opposite to each other, the number nt (rpm) of rotations during polishing is represented by a positive numerical value, and the number Nt (rpm) of revolutions during polishing is represented by a negative numerical value; and a constant-speed polishing step of performing polishing by rotating the barrel tank in a planetary manner at the number Nt (rpm) of revolutions during polishing and the number nt (rpm) of rotations during polishing that are set in a range of the following expression (4): − 1 ≤ n t / N t < 0ADVANTAGEOUS EFFECTS OF INVENTION

[0008] According to this configuration, it is possible to reduce chipping occurring in a workpiece during acceleration of a barrel tank.BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a plan view of a centrifugal barrel polishing machine according to an example. Fig. 2 is a cross-sectional view of the centrifugal barrel polishing machine. Fig. 3 is a graph showing changes over time in a number of rotations and relative centrifugal acceleration in Experiment 1. Fig. 4 is a graph showing changes over time in a number of rotations and relative centrifugal acceleration in Experiment 2. Fig. 5 is a graph showing changes over time in a number of rotations and relative centrifugal acceleration in Experiment 3. Fig. 6 is a graph showing changes over time in a number of rotations and relative centrifugal acceleration in Example 10 of Experiment 4. Fig. 7 is a graph showing changes over time in a number of rotations and relative centrifugal acceleration in Example 11 of Experiment 4. DESCRIPTION OF EMBODIMENTS

[0010] First, embodiments of the present disclosure will be listed and described. Any combination of a plurality of embodiments described below within a range not causing inconsistency is also included in the embodiments for carrying out the invention.

[0011] A method for controlling a rotation speed in centrifugal barrel polishing according to the first disclosure is [1] a method for controlling the rotation speed in centrifugal barrel polishing in which polishing is performed by rotating a barrel tank, into which a workpiece is input, in a planetary manner at a predetermined number of revolutions during polishing and a predetermined number of rotations during polishing, the method accelerating and controlling the rotation speed of the barrel tank from a rotation stop state until the rotation speed reaches the number of revolutions during polishing and the number of rotations during polishing, and the method includes an acceleration control step of: calculating a constant Ct based on the number Nt (rpm) of revolutions per minute during polishing, the number nt (rpm) of rotations per minute during polishing, a revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s 2< ) by using the following expression (1): Ct = (2πN t / 60) 2< • R / (g•n t ) ····· (1); defining a relative centrifugal acceleration F(G) based on a number N (rpm) of revolutions per minute of the barrel tank during acceleration control, the revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s 2< ) by using the following expression (2): F = 2 πN / 60 2 · R / g and changing over time the number N (rpm) of revolutions per minute of the barrel tank during the acceleration control and a number n (rpm) of rotations per minute of the barrel tank during the acceleration control so as to satisfy the following expression (3): F / n ≥ C t A centrifugal force acting on the barrel tank is proportional to the relative centrifugal acceleration F. In a case where the number N of revolutions and the number n of rotations are controlled such that the expression (3) becomes an equation, a ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations during the acceleration control is maintained at the same value as the ratio of the centrifugal force (relative centrifugal acceleration F) to the number nt of rotations during polishing. In a case where the number N of revolutions and the number n of rotations are controlled such that the expression (3) becomes an inequation, a ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations during the acceleration control is maintained at a value larger than a value of the ratio of the centrifugal force (relative centrifugal acceleration F) to the number nt of rotations during polishing. According to the present disclosure, in the acceleration control step in which the number N of revolutions and the number n of rotations of the barrel tank are increased, the occurrence of chipping caused by the ratio of the centrifugal force to the number n of rotations being smaller than the ratio of the centrifugal force to the number nt of rotations during polishing, is suppressed. [2] Preferably, the acceleration control step includes a revolution-limited acceleration step of increasing the number N (rpm) of revolutions from a rotation stop state of the barrel tank without changing the number n (rpm) of rotations. According to this configuration, the ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations increases at once immediately after the start of the acceleration control, and thus, the effect of suppressing the occurrence of chipping is high. [3] In [1] or [2], preferably, a rotation center axis of the barrel tank is in a vertical direction. In a case where the rotation center axis of the barrel tank is in a horizontal direction, a direction and magnitude of a resultant force of the centrifugal force acting on the barrel tank and the gravity vary depending on a position in a revolution path of the barrel tank. Accordingly, a flow state of a mass in the barrel tank also varies depending on the position in the revolution path of the barrel tank, and as a result, the mass flows violently, which may result in a state where chipping is likely to occur. On the other hand, in a case where the rotation center axis of the barrel tank is in a vertical direction, the centrifugal force acting on the barrel tank is always in the horizontal direction and is not affected by the gravitational acceleration acting in the vertical direction, so that it is possible to maintain a state in which chipping is less likely to occur.

[0012] A centrifugal barrel polishing method according to a second disclosure includes: [4] the acceleration control step described in [1] to [3], in which a revolution direction and a rotation direction of the barrel tank are opposite to each other, the number nt (rpm) of rotations during polishing is represented by a positive numerical value, and the number Nt (rpm) of revolutions during polishing is represented by a negative numerical value; and a constant-speed polishing step of performing polishing by rotating the barrel tank in a planetary manner at the number Nt (rpm) of revolutions during polishing and the number nt (rpm) of rotations during polishing that are set in a range of the following expression (4): − 1 ≤ n t / N t < 0 According to this configuration, occurrence of chipping of the workpiece is suppressed in the step of performing centrifugal barrel polishing by rotating the barrel tank in a planetary manner at a constant rotation speed. Therefore, it is possible to consistently suppress the occurrence of chipping during a period from the start of the acceleration control step to the end of the polishing step. <Embodiment 1>

[0013] Hereinafter, Embodiment 1 for implementing the present invention will be described with reference to Fig. 1 to Fig. 7. Fig. 1 and Fig. 2 illustrate a centrifugal barrel polishing machine 10 for executing a centrifugal barrel polishing method according to Embodiment 1. The centrifugal barrel polishing method is a method of performing polishing of a workpiece (not illustrated) in a barrel tank 12 by rotating the barrel tank 12 attached to a turret 11 in a planetary manner. The centrifugal barrel polishing method is a method of sequentially executing an acceleration control step, a constant-speed polishing step, and a deceleration control step.

[0014] As illustrated in Fig. 1 and Fig. 2, the centrifugal barrel polishing machine 10 includes a revolution shaft 13 of which the axial line is directed in a vertical direction and which rotates integrally with a turret 11, and a revolution motor 15 which transmits a rotational force to the revolution shaft 13 via a revolution belt 14. The revolution motor 15 is a motor capable of changing an output rotation speed by inverter control. The revolution shaft 13 and the turret 11 are rotationally driven by the revolution motor 15.

[0015] A plurality of barrel tanks 12 (in the present embodiment, four barrel tanks) is attached to the turret 11. The barrel tanks 12 are disposed at equal angular intervals in a circumferential direction at positions which are eccentric in a radially outward direction from a rotation center of the turret 11 (a center of the revolution shaft 13). Each barrel tank 12 can rotate integrally with a rotation shaft 16 of which the axial line is directed in the vertical direction. A rotation force of a rotation motor 18 is transmitted to the rotation shaft 16 via a rotation belt 17. The rotation motor 18 is a motor capable of changing a rotation speed by inverter control. The barrel tank 12 and the rotation shaft 16 are rotationally driven by the rotation motor 18. Each barrel tank 12 can be relatively rotated with respect to the turret 11. In a plan view when the barrel tank 12 is viewed in parallel with the revolution shaft 13 and the rotation shaft 16, an inner surface (not illustrated) of the barrel tank 12 has a regular polygon shape.

[0016] The rotation speed of the revolution motor 15 and the rotation speed of the rotation motor 18 are individually controlled by a control device 19. By rotationally driving the revolution motor 15 and the rotation motor 18 individually, the barrel tank 12 revolves integrally with the turret 11, and rotates (relatively rotates) with respect to the turret 11, thereby rotating in a planetary manner. In the plan view, a revolution direction of the barrel tank 12 (a rotation direction of the turret 11) and a rotation direction of the barrel tank 12 are opposite to each other.

[0017] In the barrel tank 12 rotating in a planetary manner, a flow layer on a surface of a mass (not illustrated) including a workpiece and polishing stones (not illustrated) flows in an avalanche-like manner, and the workpiece is polished by the polishing stones. When the flow layer of the mass is thick, chipping is likely to occur in the workpiece, and when the flow layer is thin, occurrence of chipping in the workpiece is suppressed. Therefore, in a constant-speed polishing step in which the barrel tank 12 is rotated in a planetary manner at a constant rotation speed, a number of revolutions (hereinafter, referred to as a "number Nt (rpm) of revolutions during polishing") and a number of rotations (hereinafter, referred to as a "number nt (rpm) of rotations during polishing") are set in consideration of suppression of occurrence of chipping. Specifically, the number Nt of revolutions during polishing and the number nt of rotations during polishing are set so as to satisfy the following expression (4). − 1 ≤ n t / N t < 0 Since the revolution direction and the rotation direction of the barrel tank 12 are opposite to each other, the number nt of rotations during polishing is expressed by a positive numerical value, and the number Nt of revolutions during polishing is expressed by a negative numerical value. Therefore, nt / Nt is a negative value.

[0018] The inventors of the present application have invented an acceleration control method capable of suppressing occurrence of chipping in the acceleration step from a state where rotation of the barrel tank 12 is stopped until the rotation speed of the barrel tank 12 reaches the number Nt of revolutions during polishing and the number nt of rotations during polishing. This acceleration control method has been invented based on a finding that, when a centrifugal force acting on the barrel tank 12 is weak with respect to the number of rotations of the barrel tank 12, the flow layer of the mass becomes thick and chipping is likely to occur in the workpiece, and based on experiments to be described later.[Experiment 1]

[0019] In Experiment 1, the centrifugal barrel polishing machine 10 in which the revolution radius R of the barrel tank 12 is 0.18 m was used. In the barrel tank 12, polishing stones HS-3 (not illustrated), each having a ball shape with a diameter of 3 mm and manufactured by Tipton Corp. were input, and one magnet workpiece (not illustrated) having a rectangular shape of 10 mm × 5 mm × 2 mm was input. The amount of the polishing stones input is an amount such that a volume including voids between the polishing stones is 50% of the volume of the barrel tank 12.

[0020] In Experiment 1, the number N of revolutions of the barrel tank 12 was increased (accelerated) at a constant rate so as to reach the number Nt (446 rpm) of revolutions during polishing in 30 seconds from a rotation stop state. The number Nt of revolutions during polishing is a target rotation speed to be reached for the number N (rpm) of revolutions in the acceleration control step in Examples 1 to 4. In the following description, "increasing the rotation number of the barrel tank 12" and "accelerating the rotation speed of the barrel tank 12" are used with the same meaning. A relative centrifugal acceleration F (G) based on the number N of revolutions per minute of the barrel tank 12, a revolution radius R (m) of the barrel tank 12, and gravitational acceleration g (9.8 m / s 2< ) is represented by the following expression (2). F = 2 πN / 60 2 · R / g The relative centrifugal acceleration F is proportional to the square of the number N of revolutions. In Experiment 1, the relative centrifugal acceleration F becomes 40 G after 30 seconds from the rotation stop state.

[0021] In Experiment 1, the acceleration control was performed in four examples in which the manner of increasing the number n of rotations of the barrel tank 12 was different while the manner of increasing the number N of revolutions was common. In all of these four examples, the number n (rpm) of rotations was increased so as to reach the number nt (300 rpm) of rotations during polishing in 30 seconds from the rotation stop state. The number nt of rotations during polishing is a target rotation speed to be reached for the number n of rotations in the acceleration control step in Examples 1 to 4. The results of Experiment 1 are shown in Table 1 and Fig. 3. [Table 1]Experimental Example 1Conventional Example 1Example 1Example 2Example 3Elapsed time t (sec)Number N of revolutions (rpm)Centrifugal acceleration F (G)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)0.000.000002.5-370.3252025.0-741.1508037.5-1122.575180410.0-1494.4100330712.5-1866.91255201115.0-22310.01507501717.5-26013.617510202820.0-29717.820013304522.5-33522.522516807225.0-37227.825020810011627.5-40933.627525220018730.0-44640.0300300300300Chipping occurrence rateBAAAAAAA: very low A: low B: medium

[0022] In Conventional Example 1, the number n of rotations was increased from the rotation stop state at constant acceleration, as with the number N of revolutions.

[0023] In Examples 1 to 3, the number Nt of revolutions during polishing was set to 446 rpm, the revolution radius of the barrel tank 12 was set to 0.18 m, and the number nt of rotations during polishing was set to 300 rpm. Under these conditions, a constant Ct obtained by dividing the relative centrifugal acceleration Ft during polishing by the number nt of rotations during polishing was calculated by using the following expressions (2-1) and (3'), thereby obtaining the constant Ct = 0.1334. F t = 2 πN t / 60 2 · R / g C t = F t / n t The number N of revolutions and the number n of rotations in the acceleration control step were changed over time so as to satisfy the following expressions (2) and (3-1). F = 2 πN / 60 2 · R / g F / n ≥ 0.1334

[0024] In Example 1, the number n of rotations was changed for each elapsed time so as to satisfy the following expression (5-1). n = F / 0.1334

[0025] In Example 2, from the rotation stop state to 22.5 seconds, rotation of the barrel tank 12 was stopped (a state where the number n of rotations was not increased), and for 7.5 seconds from 22.5 seconds to 30 seconds, the number n of rotations was increased at a constant rate (constant acceleration) from 0 rpm to 300 rpm. In Example 3, the number n of rotations at each elapsed time was set to a value calculated by an exponential function exp (0.1901 × each elapsed time).

[0026] The experiment of performing the acceleration control for 30 seconds as described above and then stopping the revolution and the rotation of the barrel tank 12 was repeated 40 times in each example, and the occurrence rate of chipping in the workpiece was evaluated. Among the four examples, Conventional Example 1 had the highest chipping occurrence rate, and Example 1 had the second lowest chipping occurrence rate after Conventional Example 1. The chipping occurrence rates of Example 2 and Example 3 were at the same level, and were lower than that of Example 1. The chipping occurrence rates of Conventional Example 1, Example 1, and Examples 2 and 3 were respectively evaluated as "B: medium", "A: low", and "AA: very low".

[0027] The reason why the chipping occurrence rates in Examples 1 to 3 are lower than that in Conventional Example 1 can be inferred as follows. In Conventional Example 1, since the number n of rotations was increased at a constant rate (acceleration) as with the number N of revolutions, the centrifugal force was low with respect to the number n of rotations, so that occurrence of chipping was increased. On the other hand, in Examples 1 to 3, focusing on the relative centrifugal acceleration F proportional to the square of the number N of revolutions, a constant Ct based on the number Nt of revolutions during polishing, the number nt of rotations during polishing, and the revolution radius R was calculated, and the number N of revolutions (relative centrifugal acceleration F) in the acceleration control step and the number n of rotations in the acceleration control step were changed so as to satisfy the expression: F / C t ≥ n In the graph of Fig. 3, a region on a straight line representing Example 1 and a region above the straight line of Example 1 are chipping occurrence reduction regions in which the number N of revolutions and the number n of rotations change so as to satisfy the expression including the above-described constant C t . In Fig. 3, the more the graph representing changes in the number N of revolutions and the number n of rotations bulges to the upper left, the less chipping occurs in the workpiece.[Experiment 2]

[0028] The centrifugal barrel polishing machine 10, the polishing stones, the workpiece, and the manner of increasing the number N of revolutions that are used in Experiment 2 are the same as those in Experiment 1. In Experiment 2, the acceleration control was performed in four examples in which the manner of increasing the number n of rotations of the barrel tank 12 was different while the manner of increasing the number N of revolutions was common. In all of these four examples, the number n of rotations was increased so as to reach 100 rpm in 30 seconds from the rotation stop state. The results of Experiment 2 are shown in Table 2 and Fig. 4. [Table 2]Experimental Example 2Conventional Example 2Example 4Example 5Example 6Elapsed time t (sec)Number N of revolutions (rpm)Centrifugal acceleration F (G)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)0.000.000002.5-370.380005.0-741.1172027.5-1122.52560310.0-1494.433110512.5-1866.942170715.0-22310.0502501017.5-26013.6583401520.0-29717.8674402222.5-33522.57556253225.0-37227.88369504627.5-40933.69284756830.0-44640.0100100100100Chipping occurrence rateAAAAAAAAAAAA: extremely low AA: very low A: low

[0029] In Conventional Example 2, the number n of rotations was increased from the rotation stop state at constant acceleration, as with the number N of revolutions.

[0030] In Examples 4 to 6, the number Nt of revolutions during polishing was set to 446 rpm, the revolution radius of the barrel tank 12 was set to 0.18 m, and the number nt of rotations during polishing aw set to 100 rpm. Under these conditions, a constant Ct obtained by dividing the relative centrifugal acceleration Ft during polishing by the number nt of rotations during polishing was calculated by using the following expressions (2-1) and (3'), thereby obtaining the constant Ct = 0.40003. F t = 2 πN t / 60 2 · R / g C t = F t / n t The number N of revolutions and the number n of rotations in the acceleration control step were changed over time so as to satisfy the following expressions (2) and (3-2). F = 2 πN / 60 2 · R / g F / n ≥ 0.4003

[0031] In Example 4, the number n of rotations was changed for each elapsed time so as to satisfy the following expression (5-2). n = F / 0.4003

[0032] The acceleration control step according to Example 5 includes a revolution-limited acceleration step of increasing only the number N of revolutions without changing the number n of rotations. In Example 5, from the rotation stop state up to 20 seconds, rotation of the barrel tank 12 was stopped (a state where the number n of rotations was not increased), and for 10 seconds from 20 seconds to 30 seconds, the number n of rotations was increased at a constant rate (constant acceleration) from 0 rpm to 100 rpm. In Example 6, the number n of rotations at each elapsed time was set to a value calculated by an exponential function exp (0.1535 × each elapsed time).

[0033] The experiment of performing the acceleration control for 30 seconds as described above and then stopping the revolution and the rotation of the barrel tank 12 was repeated 40 times in each example, and the occurrence rate of chipping in the workpiece was evaluated. Among the four examples, Conventional Example 2 had the highest chipping occurrence rate and was at the same level as Example 1 of Experiment 1. Example 4 had the second lowest chipping occurrence rate after Conventional Example 2, and was at the same level as Examples 2 and 3. The chipping occurrence rates of Example 5 and Example 6 were at the same level, and were lower than that of Example 4. The chipping occurrence rates of Conventional Example 2, Example 4, and Examples 5 and 6 were respectively evaluated as "A: low", "AA: very low", and "AAA: extremely low".

[0034] In Conventional Example 2 and Examples 4 to 6 of Experiment 2, the chipping occurrence rate is lower than that in Conventional Example 1 and Examples 1 to 3 of Experiment 1. The reason for this is considered to be that, while the number N of revolutions in Experiment 1 and Experiment 2 was the same, since the number nt (100 rpm) of rotations during polishing in Experiment 1 was lower than the number nt (300 rpm) of rotations during polishing in Experiment 2, a flow of the mass was more stable. Further, in the graph of Fig. 4, a region on a straight line representing Example 4 and a region above the straight line of Example 4 are a chipping occurrence reduction region in which the number N of revolutions and the number n of rotations change so as to satisfy the expression (3-2) including the above-described constant Ct.[Experiment 3]

[0035] The centrifugal barrel polishing machine 10, the polishing stones, and the workpiece that are used in Experiment 3 are the same as those in Experiments 1 and 2. Unlike Experiments 1 and 2, regarding the manner of increasing the number N of revolutions, the number N of revolutions was increased (accelerated) at a constant rate so as to reach 300 rpm in 30 seconds from the rotation stop state. In Experiment 3, the relative centrifugal acceleration F becomes 18 G after 30 seconds from the rotation stop state.

[0036] In Experiment 3, the acceleration control was performed in four examples in which the manner of increasing the number n of rotations of the barrel tank 12 was different while the manner of increasing the number N of revolutions was common. In all of these four examples, the number n of rotations was increased so as to reach 300 rpm in 30 seconds from the rotation stop state. The results of Experiment 3 are shown in Table 3 and Fig. 5. [Table 3]Experimental Example 3Conventional Example 3Example 7Example 8Example 9Elapsed time t (sec)Number N of revolutions (rpm)Centrifugal acceleration F (G)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)Number n of rotations (rpm)0.000.000002.5-250.1252025.0-500.5508037.5-751.175180410.0-1002.0100330712.5-1253.11255201115.0-1504.51507501717.5-1756.217510202820.0-2008.020013304522.5-22510.222516807225.0-25012.625020810011627.5-27515.227525220018730.0-30018.1300300300300Chipping occurrence rateCBAAA: low B: medium C: high

[0037] In Conventional Example 3, the number n of rotations was increased from the rotation stop state at constant acceleration, as with the number N of revolutions.

[0038] In Examples 7 to 9, the number Nt of revolutions during polishing was set to 300 rpm, the revolution radius of the barrel tank 12 was set to 0.18 m, and the number nt of rotations during polishing was set to 300 rpm. Under these conditions, a constant Ct obtained by dividing the relative centrifugal acceleration Ft during polishing by the number nt of rotations during polishing was calculated by using the following expressions (2-1) and (3') , thereby obtaining the constant Ct = 0.0604. F t = 2 πN t / 60 2 · R / g C t = F t / n t The number N of revolutions and the number n of rotations in the acceleration control step were changed over time so as to satisfy the following expressions (2) and (3-3). F = 2 πN / 60 2 · R / g F / n ≥ 0.0604

[0039] In Example 7, the number n of rotations was changed for each elapsed time so as to satisfy the following expression (5-3). n = F / 0.0604

[0040] The acceleration control step according to Example 10 includes a revolution-limited acceleration step of increasing only the number N of revolutions without changing the number n of rotations. In Example 8, from the rotation stop state to 22.5 seconds, rotation of the barrel tank 12 was stopped (a state where the number n of rotations was not increased), and for 7.5 seconds from 22.5 seconds to 30 seconds, the number n of rotations was increased at a constant rate (constant acceleration) from 0 rpm to 300 rpm. In Example 9, the number n of rotations at each elapsed time was set to a value calculated by an exponential function exp (0.1901 × each elapsed time).

[0041] The experiment of performing the acceleration control for 30 seconds as described above and then stopping the revolution and the rotation of the barrel tank 12 was repeated 40 times in each example, and the occurrence rate of chipping in the workpiece was evaluated. The chipping occurrence rate was the highest in Conventional Example 3 among the four examples. Example 7 had the second lowest chipping occurrence rate after Conventional Example 3, and was at the same level as Conventional Example 1. The chipping occurrence rates of Example 8 and Example 9 were at the same level, were lower than that in Example 7, and were at the same level as those in Example 1 and Conventional Example 2. The chipping occurrence rates of Conventional Example 3, Example 7, and Examples 8 and 9 were respectively evaluated as "C: high", "B: medium", and "A: low".

[0042] In Conventional Example 3 and Examples 7 to 9 of Experiment 3, the chipping occurrence rates were overall higher than those in Conventional Example 1 and Examples 1 to 3 of Experiment 1. The reason for this is considered to be that, the flow of the mass was unstable since the number Nt (300 rpm) of revolutions during polishing in Experiment 3 was lower than the number Nt (446 rpm) of revolutions during polishing in Experiment 1 and the relative centrifugal acceleration F (18.1 G) in Experiment 3 was also lower than the relative centrifugal acceleration F (40 G) in Experiment 1,.

[0043] In the graph of Fig. 5, a region on a straight line representing Example 7 and a region above the straight line of Example 4 are a chipping occurrence reduction region in which the number N of revolutions and the number n of rotations change so as to satisfy the expression (3-3) including the above-described constant C t . In Examples 7 to 9, since the number N of revolutions and the number n of rotations were changed in the chipping occurrence reduction region, the chipping occurrence rate is lower than that in Example 3.[Experiment 4]

[0044] The centrifugal barrel polishing machine 10, the polishing stones, and the workpiece that are used in Experiment 4 are the same as those in Experiments 1 to 3. Unlike Experiments 1 to 3, regarding the manner of increasing the number N of revolutions, the number N of revolutions was increased (accelerated) at a constant rate so as to reach the number Nt (446 rpm) of revolutions during polishing in 15 seconds from the rotation stop state, and thereafter, the number Nt of revolutions during polishing was maintained from 15 seconds to 30 seconds.

[0045] In Experiment 4, the acceleration control was performed in two examples in which the manner of increasing the number n of rotations of the barrel tank 12 was different while the manner of increasing the number N of revolutions was common. In all of these two examples, the number n of rotations was increased so as to reach 300 rpm in 30 seconds from the rotation stop state. The results of Experiment 4 are shown in Table 4 and Fig. 6 and Fig. 7. [Table 4]Experimental Example 4Example 10Example 11Elapsed time t (sec)Number N of revolutions (rpm)Centrifugal acceleration F (G)Number n of rotations (rpm)Number n of rotations (rpm)0.000.0002.5-741.1035.0-1494.40137.5-22310.002810.0-29717.805012.5-37227.807815.0-44640.0011317.5-44640.05015320.0-44640.010020022.5-44640.015022525.0-44640.020025027.5-44640.025027530.0-44640.0300300Chipping occurrence rateAAAAAA: very low

[0046] The acceleration control step according to Example 10 includes a revolution-limited acceleration step of increasing only the number N of revolutions without changing the number n of rotations. In Example 10, for 15 seconds from the rotation stop state until the number N of revolutions reached the number Nt of revolutions during polishing, rotation of the barrel tank 12 was stopped (a state where the number n of rotations was not increased), and for 15 seconds from 15 seconds to 30 seconds, the number n of rotations was increased at a constant rate (constant acceleration) from 0 rpm to 300 rpm. Fig. 6 illustrates a pattern of changes in the number N of revolutions and the number n of rotations in Example 10. The chipping occurrence rate of Example 10 was "AA: very low".

[0047] In Example 11, for 15 seconds from the rotation stop state until the number N of revolutions reaches the number Nt (446 rpm) of revolutions during polishing, the number N of revolutions and the number n of rotations are changed so as to satisfy the following expression (3-4) using a constant Ca larger than the constant Ct (0.1334) of Example 1. F / n = Ca From 15 seconds to 30 seconds, the number n of rotations was increased while maintaining the number Nt of revolutions during polishing. Fig. 7 illustrates a pattern of changes in the number N of revolutions and the number n of rotations in Example 11. The chipping occurrence rate of Example 11 was "AA: very low".[Experiment 5]

[0048] In Experiment 5, barrel polishing was performed by using the same centrifugal barrel polishing machine 10 as in Experiments 1 to 4. In the barrel polishing, the same polishing stones HS-3 as those in Experiments 1 to 4 were input into the barrel tank 12 in an amount of 50 vol%, and ten of the same magnet workpieces as those in Experiments 1 to 4 were input into the barrel tank 12.

[0049] In Example 12, after the acceleration control of the number N of revolutions and the number n of rotations of the barrel tank 12 was performed in the same manner as in Conventional Example 1, polishing was performed for 5 minutes at the number Nt of revolutions during polishing and the number nt of rotations during polishing that were the same as those in Conventional Example 1. In Example 13, after the acceleration control of the number N of revolutions and the number n of rotations of the barrel tank 12 was performed in the same manner as in Conventional Example 2, polishing was performed for 5 minutes at the number Nt of revolutions during polishing and the number nt of rotations during polishing that were the same as those in Conventional Example 2. In Example 14, after the acceleration control of the number N of revolutions and the number n of rotations of the barrel tank 12 was performed in the same manner as in Conventional Example 3, polishing was performed for 5 minutes at the number Nt of revolutions during polishing and the number nt of rotations during polishing that were the same as those in Conventional Example 3.

[0050] In each of Examples 12 to 14, work of measuring the chipping occurrence rate and the edge roundness amount after performing polishing for five minutes was repeated ten times. The edge roundness amount is a radius at the center of a corner edge having a length of 10 mm in the length direction, among corner edges of an outer surface of the magnet workpiece. The numerical values of the chipping occurrence rate and the edge roundness amount of the corner portion that are shown in Table 5 are average values of 10 pieces × 10 times = 100 values. [Table 5]ItemExample 12Example 13Example 14Acceleration conditionSame as in Conventional Example 1Same as in Conventional Example 2Same as in Conventional Example 3Number Nt of revolutions during polishing (rpm)-446-446-300Relative centrifugal acceleration F (G)404018Number n t of rotations during polishing (rpm)300100300n t / N t -0.67-0.22-1Chipping occurrence rate (%)16827Edge roundness amount (µm)955859

[0051] The number nt of rotations during polishing is the same in Example 12 and Example 14, but the chipping occurrence rate in Example 12 is lower than that in Example 14. In Example 12, the edge roundness amount of the corner portion of the workpiece is approximately 1.5 times greater than that in Example 14, the edge roundness amount being a polishing amount. The reason for this is considered to be that, in Example 12, since the relative centrifugal acceleration F was large, the mass was pressed against an inner wall of the barrel tank 12, thereby reducing a thickness of the flow layer, so that the workpieces flowed stably in the mass.

[0052] In Example 12 and Example 13, the number Nt of revolutions during polishing is the same, but the chipping occurrence rate in Example 13 is lower than that in Example 12. In addition, the edge roundness amount in Example 13 is smaller than that in Example 12, and is equivalent to that in Example 14. The reason for this is considered to be that, since the number nt of rotations during polishing in Example 13 was smaller than that in Example 12, in Example 13, as compared with Example 12, the mass was pressed against the outer side of the inner wall of the barrel tank 12 and the thickness of the flow layer was further reduced due to the lower number n t of rotations during polishing, so that the workpieces flowed extremely slowly and stably in the mass.

[0053] The method for controlling rotation speed according to Embodiment 1 is a method of accelerating and controlling the rotation speed of the barrel tank 12 from a rotation stop state until the rotation speed reaches the number Nt of revolutions during polishing and the number nt of rotations during polishing, in centrifugal barrel polishing in which polishing is performed by rotating the barrel tank 12, into which a workpiece is input, in a planetary manner at a predetermined number Nt of revolutions per minute during polishing and a predetermined number nt of rotations per minute during polishing.

[0054] This acceleration control method includes the following acceleration control step. In this acceleration control step, a constant Ct based on the number Nt of revolutions per minute during polishing, the number nt of rotations per minute during polishing, the revolution radius R of the barrel tank 12, and gravitational acceleration g is calculated by the following expression (1). C t = 2 πN t / 60 2 · R / g · n t Further, the relative centrifugal acceleration F based on the number N of revolutions per minute of the barrel tank 12 during the acceleration control, the revolution radius R of the barrel tank 12, and gravitational acceleration g is defined by using the following expression (2). F = 2 πN / 60 2 · R / g Then, the number N of revolutions per minute of the barrel tank 12 during the acceleration control and the number n of rotations per minute of the barrel tank 12 during the acceleration control are changed over time so as to satisfy the following expression (3). F / n ≥ C t

[0055] A centrifugal force acting on the barrel tank 12 is proportional to the relative centrifugal acceleration F. In a case where the number N of revolutions and the number n of rotations are controlled such that the expression (3) becomes an equation, a ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations during the acceleration control is maintained at the same value as the ratio of the centrifugal force (relative centrifugal acceleration F) to the number nt of rotations during polishing. In a case where the number N of revolutions and the number n of rotations are controlled such that the expression (3) becomes an inequation, a ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations during the acceleration control is maintained at a value larger than a value of the ratio of the centrifugal force (relative centrifugal acceleration F) to the number nt of rotations during polishing. According to Embodiment 1, in the acceleration control step in which the number N of revolutions and the number n of rotations of the barrel tank 12 are increased, the occurrence of chipping caused by the ratio of the centrifugal force to the number n of rotations being smaller than the ratio of the centrifugal force to the number nt of rotations during polishing, is suppressed.

[0056] The acceleration control step in Examples 2, 5, 8, and 10 includes a revolution-limited acceleration step of increasing the number N of revolutions without changing the number n of rotations from a state where the rotation and revolution of the barrel tank 12 are stopped. According to this control step, the ratio of the centrifugal force (relative centrifugal acceleration F) to the number n of rotations can be maintained at a high value immediately after the start of the acceleration control, and thus, the effect of suppressing the occurrence of chipping is high.

[0057] In a case where the rotation center axis of the barrel tank 12 is in a horizontal direction, a direction and magnitude of a resultant force of the centrifugal force acting on the barrel tank 12 and the gravity vary depending on a position in the revolution path of the barrel tank 12. Accordingly, the flow state of the flow layer of the mass in the barrel tank 12 also varies depending on the position in the revolution path of the barrel tank 12, and as a result, the mass flows violently, which may result in a state where chipping is likely to occur. In view of this point, in Embodiment 1, the axial lines of the revolution shaft 13 and the rotation shaft 16, which are the rotation center axes of the barrel tank 12, are set in the vertical direction. In a case where the rotation center axis of the barrel tank 12 is set in the vertical direction, the centrifugal force acting on the barrel tank 12 is always in the horizontal direction, and is not affected by the gravitational acceleration acting in the vertical direction, so that it is possible to maintain a state where chipping is less likely to occur.

[0058] In the centrifugal barrel polishing method according to Embodiment 1, Examples 12, 13, and 14 include the acceleration control step and a constant-speed polishing step. When the number of revolutions of the barrel tank 12 during polishing is defined as a number Nt of revolutions during polishing, and the number of rotations of the barrel tank 12 during polishing is defined as a number nt of rotations during polishing, in the constant-speed polishing step, the barrel tank 12 was rotated in a planetary manner at the number Nt of revolutions during polishing and the number nt of rotations during polishing, that were set within a range of the following expression (4). − 1 ≤ n t / N t < 0 The revolution direction and the rotation direction of the barrel tank 12 are opposite to each other, the number nt of rotations during polishing is a positive numerical value, and the number Nt of revolutions during polishing is a negative numerical value. Therefore, nt / Nt is a negative value. As shown in Table 5, in all of Examples 12, 13, and 14, the value of nt / Nt satisfies the above expression. According to the barrel polishing method of Embodiment 1, occurrence of chipping of the workpiece is suppressed in the constant-speed polishing step of performing centrifugal barrel polishing by rotating the barrel tank 12 in a planetary manner at a constant rotation speed. Therefore, it is possible to consistently suppress the occurrence of chipping in the barrel tank 12 during a period from the start of the acceleration control step to the end of the polishing step.<Other Embodiments>

[0059] The present invention is not limited to Embodiment 1 described with reference to the description and drawings, and for example, the following embodiments are also included in the technical scope of the present invention.

[0060] In the barrel polishing machine according to Embodiment 1, the rotation axis direction of the barrel tank is in the vertical direction, but the axial line directions of the rotation axes (the revolution axis and the rotation axis) of the barrel tank may be in the horizontal direction. Even in a case where the rotation axis of the barrel tank is set in the horizontal direction, the chipping occurrence rate can be reduced according to the acceleration control method of the present disclosure, as compared with the conventional acceleration method.

[0061] In the acceleration control step of Experiments 1 to 4, the number N of revolutions is increased until the relative centrifugal acceleration F reaches a target value of 18 G or 40 G, but the target value to be reached of the relative centrifugal acceleration F in the acceleration control step may be around 5 G to 15 G which is a conventional centrifugal barrel polishing region. Also in this case, in the polishing step, it is preferable that a value obtained by dividing the number n of rotations by the number N of revolutions is set so as to satisfy -1 ≤ n / N < 0.

[0062] In Conventional Examples 1 to 3 and Examples 1 to 14 of Embodiment 1 described above, the workpiece and the polishing stones are input into the barrel tank, and the workpiece is polished by the polishing stones. On the other hand, "co-grinding polishing" in which only the workpieces are input into the barrel tank and the workpieces come into contact with each other and are polished against each other may be used. Also in this case, occurrence of chipping in the workpiece can be suppressed by the acceleration control method according to the present disclosure.

[0063] In a deceleration step after the constant-speed polishing step, occurrence of chipping during the deceleration step can be suppressed by setting a relative centrifugal acceleration obtained by substituting the number Nt of revolutions during polishing into the expression (2) as Ft, and by performing deceleration control such that the number n of rotations per minute of the barrel tank are changed over time so as to satisfy the following expression (5). F ≥ F t − C t ⋅ nREFERENCE SIGNS LIST

[0064] 10Centrifugal barrel polishing machine 12Barrel tank 13Revolution shaft (rotation center axis) 16Rotation shaft (rotation center axis)

Claims

1. A method for controlling a rotation speed in centrifugal barrel polishing in which polishing is performed by rotating a barrel tank, into which a workpiece is input, in a planetary manner at a predetermined number of rotations during polishing and a predetermined number of revolutions during polishing, the method accelerating and controlling the rotation speed of the barrel tank from a rotation stop state until the rotation speed reaches the number of revolutions during polishing and the number of rotations during polishing, the method comprising an acceleration control step of: calculating a constant Ct based on the number Nt (rpm) of revolutions per minute during polishing, the number nt (rpm) of rotations per minute during polishing, a revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s2) by using the following expression (1): C t = 2 πN t / 60 2 · R / g · n t defining a relative centrifugal acceleration F(G) based on a number N (rpm) of revolutions per minute of the barrel tank during acceleration control, the revolution radius R (m) of the barrel tank, and gravitational acceleration g (9.8 m / s2) by using the following expression (2): F = 2 πN / 60 2 · R / gand changing over time the number N (rpm) of revolutions per minute of the barrel tank during the acceleration control and a number n (rpm) of rotations per minute of the barrel tank during the acceleration control so as to satisfy the following expression (3): F / n ≥ C t 2. The method for controlling the rotation speed in centrifugal barrel polishing according to claim 1, wherein the acceleration control step includes a revolution-limited acceleration step of increasing the number N (rpm) of revolutions from a rotation stop state of the barrel tank without changing the number n (rpm) of rotations.

3. The method for controlling the rotation speed in centrifugal barrel polishing according to claim 1 or 2, wherein a rotation center axis of the barrel tank is in a vertical direction.

4. A centrifugal barrel polishing method comprising: the acceleration control step according to claim 1 or 2, in which a revolution direction and a rotation direction of the barrel tank are opposite to each other, the number nt (rpm) of rotations during polishing is represented by a positive numerical value, and the number Nt (rpm) of revolutions during polishing is represented by a negative numerical value; and a constant-speed polishing step of performing polishing by rotating the barrel tank in a planetary manner at the number Nt (rpm) of revolutions during polishing and the number nt (rpm) of rotations during polishing that are set in a range of the following expression (4): − 1 ≤ n t / N t < 0

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