Balancing method and means for rotary units

Abstract: A method is described for balancing and then retaining a rotatable unit in a dynamically balanced condition. In each end of the unit, there is an annular channel (16) concentric with the rotational axis encircled by a flexible rim (12a). A plurality of balls (17) of substantially identical size and weight are inserted in an outer portion of each channel in which the balls are freely movable. While the unit is rotated at a speed above resonance, a balancing instrument is used to determine the mass magnitude and angle necessary to dynamically balance the unit. Then the balls are circumferentially relocated by vector balancing to provide mass at points equivalent to the determined mass and angle. The relocated balls are then forced axially past an interference ridge (20) and into an inner portion of the respective channel in which the rim is flexed and the balls are held against movement.

Description: This invention relates to methods and means for balancing a rotary unit, and relates more particularly to a method and means for dynamically balancing and then retaining a rotatable unit, such as a disk file, in dynamically balanced condition. The balance correction techniques traditionally used for rotatable units involve adding or removing weights or bending a tab or the like to adjust the center of mass. The technique currently in widespread use to retain rotatable units, such as magnetic disk files, in dynamically balanced condition is to adhesively secure weights of selectable magnitude at different locations around the hub after the magnitude and angle of the weights needed for balance are calculated by a balancing instrument. U.S. patent 4,075,909 discloses a plurality of balls movable within an annular raceway to adjust rotating shaft imbalance upon flexure of a radially movable floating inertia ring. When balance is achieved by repositioning of the balls, the inertia ring rotates concentrically with the shaft to trap each ball in circumferential position. This technique has the following disadvantages: (1) reduced sensitivity due to the need to overcome finger spring loads before the balls are free; (2) need for the balls to overcome friction to roll to a position of lesser imbalance; (3) reliance on precision of the inertia ring for minimum imbalance; (4) limited balance resolution dependent upon the circumferential spacing of slots in the periphery of the ring; (5) complexity of design and assembly; and finally (6) it requires use with a flexible shaft. Another technique is disclosed in Russian patent 693,136. It uses an electromagnet to generate wall oscillations so that ball weights can move freely in a damping liquid sealed in an annular cavity to compensate for rotor imbalance; whereupon the balls are locked in their positions by the electromagnet. U.S. patent 4,060,009 describes a method of balancing a rotatable hollow shaft by providing within the shaft a sealed housing containing an annular cavity. In the cavity are a plurality of balls and a thermo-setting adhesive. When rotated above resonance, the balls reposition themselves within the cavity to counteract the out-of-balance condition; whereupon a heating coil or the like heats and sets the resin to retain the balls as repositioned. This technique will not dynamically balance with requisite precision because the liquid adhesive creates friction that will resist proper positioning of the balls. Also, implementation of this technique is costly. There is a need for an improved balance correction method and means which eliminates the need for damping liquids or adhesives; achieves balancing more simply and rapidly and with more precision than methods and means heretofore proposed; and is especially suitable for dynamically balancing disk files which have rigid shafts. According to the present invention a rotary unit is provided which carries a balancing device having one or more members which form an annular channel concentric with the rotational axis of the unit, the balancing device including a plurality of balls moveable along a balancing track in the annular channel to dynamically balance the rotary unit characterised in that the annular channel is shaped to incorporate a holding track spaced along the rotational axis of the unit from the balancing track, the member or members forming the channel being flexible to permit the balls to be forced out of the balancing track and into the holding track, the holding track being shaped to hold the balls against movement by pressure resulting from the flexure of the channels. Further according to the present invention there is provided a magnetic disk file comprising a plurality of magnetic disks mounted on a rotary shaft and provided with balancing means to dynamically balance the disk file, characterised in that the balancing means include one or more members constituting an annular channel concentric with the rotational axis of the rotary shaft, a plurality of balls moveable along a balancing track in the annular channel to dynamically balance the disk file, the annular channel being shaped to incorporate a holding track portion spaced along the rotational aixs of the shaft from the balancing track, the member or members of the channel being flexible to permit the balls to be forced over an interference ridge out of the balancing track and into the holding track portion, the holding track portion being shaped to hold the balls against movement by pressure resulting from the flexure of the channel. Yet further according to the invention there is provided a method of balancing a rotatable unit, comprising the steps of: providing in at least one end of the unit a track in a channel encircling the rotational axis; inserting in the track a plurality of balls of substantially identical size and weight which normally are free to move around the track; while rotating the unit at a speed above resonance, determining the magnitude of the imbalance of the unit; circumferentially relocating the balls by vector balancing to provide mass at angular points equivalent to the determined imbalance; characterised in that the method includes the further step of forcing the circumferentially relocated balls axially from the track over an interference ridge and further into the channel to a position in which the balls as circumferentially relocated are held against movement. Brief Description of the Drawings Fig. 1 is a perspective cut-away view of a rotatable unit embodying the invention; Fig. 2 is a sectional view of part of the unit of Fig. 1 showing to enlarged scale a portion of a clamp ring showing a ball in an outer annular channel; Fig. 3 is a sectional view to the same enlarged scale of the clamp ring of Fig. 2 flexed to clamp a ball in an inner annular channel; and Figs. 4A, 4B and 4C illustrate the steps in vector balancing of the unit of Figs. 1 to 3. As illustrated in Fig. 1, a rotatable unit 10 embodying the invention comprises a hub 11 having at one end an integral flange 12 and at the other end a clamp ring 13 suitably affixed to the hub at 14. Hub 11 is rotatably mounted on a rigid spindle or shaft 15, supported in bearings and rotated by conventional means (not shown). In the outer (i.e., non-adjacent) ends of both flange 12 and clamp ring 13 are annular channels 16 concentric with the shaft axis. In each channel 16 are a plurality of balls 17 of substantially identical weight and size. Each channel is in part defined by the flexible outer rim 12a or 13a of flange 12 or ring 13, respectively. As best shown in Fig. 2, each channel 16 has an outer portion providing a V-notched balancing track 18 into which the balls 17 are manually insertable by flexing rim 13a (or 12a); whereupon they are freely movable without falling out of the channel. Each channel 16 also has an inner holding track portion 19 defined in part by an interference ridge 20 adjacent the inner edge of track 18. When balls 17 are forced axially, rim 13a (or 12a) will flex and permit the balls to move from track 18 past interference ridge 20 into inner holding track portion 19, as shown in Fig. 3. Once past ridge 20, the balls will be retained against movement by the pressure of rim 13a (or 12a). Channels 16 and balls 17 are provided in each end of rotatable unit 10, so it can be dynamically balanced, as dynamic balancing requires balancing in two planes. In operation, a conventional microprocessor-based dynamic balancing instrument, such as the CAB 570 Model marketed by Schenck-Treble Corporation of Deer Park, New York, is used to measure imbalance of unit 10. The unit is rotated at a speed above resonance while balls 17 are freely movable in their respective tracks 18. The instrument then determines the imbalance magnitude and angle (see X, Fig. 4A) relative to a rotation time reference on index mark I. To compensate for this out-of-balance condition, balls 17 are positioned by vector balancing (see Figs. 4B, 4C) to provide the compensating mass and ball spacing (i.e., the angular position of the balls) necessary to center mass X at the axis of rotation of the shaft, in the following manner. While unit 10 is rotating, the balls 17 and hence mass X are repositioned, such as by applying an external force in the direction of movement or relocation to slip the balls circumferentially relative to the rotating unit. This external force may be applied on the balls by a magnetic force or applied by air under pressure directed through a nozzle. Upon achieving dynamic balance the balls are forcibly relocated from each track 18 over each ridge 20 into the respective inner holding track portion 19 of flange 12 and clamp ring 13 (see Fig. 3); whereupon they will be retained, as above explained, against further movement to maintain the dynamic balance. This forcing of the balls into the inner channel portion 19 can be achieved by stopping rotation of the unit 10 after the angular position of the balls has been determined for the compensating mass is determined by the balancing instrument. Then the balls are manually forced into desired circumferential positions for the appropriate angle. Alternatively, while the unit 10 is being rotated, the necessary force may be applied by activating an appropriate insertion means (not shown) such as a solenoid-actuated axially movable coaxially rimmed plate that can enter the channel and act on the balls simultaneously. Rims 12a, 13a are sufficiently flexible that only a low force is required to snap the balls into inner holding track portion 19. Balls can be removed from the inner and outer tracks portions 19 and 18 by withdrawing the balls axially with a device which captures and holds the balls. Extraction is accomplished by overcoming the resistance of the pressure applied by the respective rim 12a or 13a. The technique herein described is especially suitable for dynamically balancing magnetic disk files. In such case a series of spaced magnetic disks (not shown) would be mounted on hub 11 and clamped between flange 12 and ring 13. However, such an application is to be considered as merely illustrative.

Claims: A rotary unit carrying a balancing device having one or more members which form an annular channel (16) concentric with the rotational axis of the unit, the balancing device including a plurality of balls (17) moveable along a balancing track (18) in the annular channel to dynamically balance the rotary unit characterised in that the annular channel is shaped to incorporate a holding track (19) spaced along the rotational axis of the unit from the balancing track (18), the member or members forming the channel (16) being flexible to permit the balls (17) to be forced out of the balancing track (18) and into the holding track (19), the holding track (19) being shaped to hold the balls (17) against movement by pressure resulting from the flexure of the channels (16). A rotary unit according to claim 1 further characterised in that an interference ridge (19) is situated between the balancing track (18) and the holding track (19), the balls (17) being moveable over the ridge (19) from the balancing track (18) to the holding track (19). A rotary unit according to Claim 1 or 2 further characterised in that the channel (16) has a flexible rim (12a) which encircles the tracks in the channel. A rotary unit according to claim 1, 2 or 3 further characterised in that the holding track (19) is disposed deeper in the channel (16) than the balancing track (18). A magnetic disk file comprising a plurality of magnetic disks mounted on a rotary shaft (15) and provided with balancing means to dynamically balance the disk file, characterised in that the balancing means include one or more members constituting an annular channel (16) concentric with the rotational axis of the rotary shaft (16), a plurality of balls (17) moveable along a balancing track (18) in the annular channel (16) to dynamically balance the disk file, the annular channel being shaped to incorporate a holding track portion (19) spaced along the rotational aixs of the shaft (15) from the balancing track (18), the member or members of the channel (16) being flexible to permit the balls (17) to be forced over an interference ridge (19) out of the balancing track (18) and into the holding track portion (19), the holding track portion (19) being shaped to hold the balls (17) against movement by pressure resulting from the flexure of the channel (16). A method of balancing a rotatable unit, comprising the steps of: providing in at least one end of the unit a track (18) in a channel (16) encircling the rotational axis; inserting in the track (18) a plurality of balls (17) of substantially identical size and weight which normally are free to move around the track; while rotating the unit at a speed above resonance, determining the magnitude of the imbalance of the unit; circumferentially relocating the balls (17) by vector balancing to provide mass at angular points equivalent to the determined imbalance; characterised in that the method includes the further step of forcing the circumferentially relocated balls (17) axially from the track (18) over an interference ridge (19) and further into the channel (16) to a position in which the balls as circumferentially relocated are held against movement.

Inventors: CAMERON T JAY, ERICKSON ELWYN GRANT, HEMPHILL CORNEALIUS HERMAN, CAMERON, T. JAY, ERICKSON, ELWYN GRANT, HEMPHILL, CORNEALIUS HERMAN
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1990
Main classification: G01M1
IPC codes: F16F15, G11B17, G11B33, G11B19, G01M1, G11B25