WO1997006528A1

WO1997006528A1 - Method and apparatus for launching and retracting read-write heads from the medium of a disk drive

Info

Publication number: WO1997006528A1
Application number: PCT/US1996/012464
Authority: WO
Inventors: Duncan L. Pollock; Hans K. Tannert
Original assignee: Syquest Technology, Inc.
Priority date: 1995-08-03
Filing date: 1996-07-30
Publication date: 1997-02-20

Abstract

A single mechanism is used to launch and retract the read-write heads from the medium of a disk drive. The mechanism includes a retraction lever (91), a retraction lever lock (118), a mechanical biasing member (76), a disk (37), and a voice coil motor (16). During launch of the read-write heads, the mechanical biasing member balances the emf generated by the voice coil motor. After launch, the voice coil motor is used to rotate a retraction lever and increase the potential energy in the mechanical biasing member. The retraction lever lock then is used to store this built-up potential energy. If the drive later experiences a loss of power, the mechanism automatically retracts the read-write heads from the media. During retraction of the read-write heads, the stored mechanical energy is applied to the retraction lever, which then automatically retracts the read-write heads.

Description

DESCRIPTION

Method and Apparatus for Launching and Retracting Read-Write Heads from the Medium of a Disk Drive

This is a continuation-in-part of the application, Serial No. 08/282,276, filed on July 27, 1994.

Field of the Invention

The present invention relates to a disk drive and in particular to a method and apparatus capable of launching and retracting the heads in the disk drive. This invention can be used with rigid or floppy disk drives using fixed or removable media.

Background Art In the early and mid-1970s, almost all drives used removable media. Since the early 1980s, however, most drives use fixed media. In these fixed media drives, there has been little concern with removing the heads from the proximity of the media when access to data is unnecessary. Recently, there has been a trend back to removable media. This trend has resurrected the problem of launching and retracting the read-write heads.

Removable cartridge disk drives must be able to accurately, smoothly, and efficiently load the read-write heads onto the media, which is generally protected in a disk cartridge. Further, it is desirable to be able to remove the heads from the media both when the operator has voluntarily finished using the cartridge in the drive, and when the drive experiences an unexpected loss of power during use. If the read-write heads land on the surface of the disk when the motor spins down during power loss, this may cause the heads to stick to the disk if the heads are left on the disk for a long period of time before power is restored to the drive. This phenomenon is known as stiction. Additional damage may occur during transportation of a disk drive when the read-write heads are left on a disk surface. It is thus desirable for the heads to be automatically removed from the cartridge without damaging the heads or the memory media in the process whenever power is removed from the drive.

In the past, various methods have been employed to control the power-on and power-off "retracting" of the heads off of the media. With many prior art drives, it is very difficult to remove a cartridge from the drive when power loss occurs, let alone to retract the read-write heads from the media, which is generally a prerequisite to being capable of removing the cartridge without risking damage to the recording media, the read-write heads, or both, and concomitant loss of data. In the past, various methods also have been used to control the "launching" of the heads in disk drives that employ removable disk cartridges. For example, U.S. Patent No. 4,870,518, issued September 26, 1989, and assigned to the assignee of the instant application, is directed to two different methods that may be used to control head launching speed in a removable cartridge disk drive. U.S. Patent No. 4,870,518 is incorporated by reference as though fully disclosed herein. One of the methods disclosed in this patent employs a dash pot or air damper to control the launch velocity of the read-write heads. The use of precision air dampers, however, increases the cost of the drive, and these dampers do not remove the heads automatically during a loss of power.

Other prior art drives use velocity feedback based on back emf (electromotive force) or tachometer data from the head actuator assembly. Such drives monitor the velocity of the readwrite heads during the launching process. An example of controlling head launch velocity using back emf generated by the movement of the actuator is described in U.S. Patent No. 4,864,437, which is owned by the assignee of the present invention and the disclosure of which is incorporated herein by reference. The use of these devices also increases the cost of the drive, and does not help remove the heads automatically after the drive loses power. It is also difficult to accurately detect back emf during low speed movement, such as during the loading of read-write heads.

Each of the prior art methods of controlling the launch velocity of the read-write heads are complex, which increases the potential for failure of the drive. In addition, these prior art devices are costly to incorporate into drives.

Therefore, there currently exists a need for a better method of controlling the velocity of the actuator during head launch, of controlling the velocity of the actuator during head retraction, and of storing sufficient energy to automatically retract the read-write heads in the event of power failure.

Summary of the Invention

Accordingly, a general object of the present invention is to provide in disk drives an improved method and apparatus for launching and retracting read-write heads, in which the abovedescribed problems and disadvantages have been considered and mitigated.

Another object of the present invention is to provide a read-write head launching apparatus that uses electromotive force (emf) produced in the coil of the actuator motor to incrementally balance the tension in a retraction spring and the friction on the guiding surfaces of the head unload arm to allow velocity control of the head arm assembly during launch. A further object of the present invention is to provide a read-write head retraction apparatus that uses other than electrical energy to remove the read-write heads from the disk surface any time the drive experiences a loss of power. A still further object of the present invention is to provide a read-write head launching and retracting apparatus that is able to automatically retract the read¬ write heads if the drive experiences a loss of power, thereby lifting the heads away from the disk surface without damaging either the read-write heads or disk, or both. When the heads are thus lifted from the disk surface, the phenomena called stiction is also eliminated. In order to achieve the above and other objects of the present invention, an apparatus is provided for launching the read-write head onto and for retracting the read-write heads from a disk within a disk drive. The disk may be mounted within a cartridge. The apparatus includes a read-write head attached to a head arm assembly, a pivotally-mounted retraction lever having a pressing end and a trappable end, wherein the retraction lever is positioned such that the pressing end is adjacent to a pressing surface of the head arm assembly, and a mechanical biasing member (e.g., a spring) that biases the pressing end of the retraction lever toward the pressing surface of the head arm assembly. In a preferred embodiment of the present invention, the retraction lever is tapered. In another embodiment, a sleeve of energy-absorbing material is attached to the pressing end of the retraction lever. A retraction lever lock is provided to alternately trap and release the trappable end of the retraction lever, and a solenoid is attached to the retraction lever lock to position the retraction lever lock. A voice coil motor is operatively associated with the head arm assembly and is used both to launch the read¬ write heads and to position the read-write heads for writing data to a disk or reading data from a disk. The apparatus also includes a head unload arm comprising a forked portion having an upper guiding surface and a lower guiding surface.

Additional objects, advantages, and features of the present invention will further become apparent to persons skilled in the art from a study of following description and of the accompanying drawings. Brief Description of the Drawings

Figs. 1-8 are top elevational diagrammatic views of an embodiment of the instant invention, showing the head launching and retracting apparatus at various points during operation of the apparatus;

Fig. 9 is an enlarged cross-sectional view of the forked portion of the head unload arm as referenced in Figs. 3 and 16;

Fig. 10 is a three-dimensional view of the head arm assembly, voice coil motor, retraction lever, retraction spring, retraction lever lock, head unload arm, and head unload arm guide;

Fig. 11 is an elevational view of the top of the retraction spring hook; Fig. 12 is an elevational view of the side of the retraction spring hook, depicting the spring-retaining groove formed in the upright portion of the retraction spring hook;

Fig. 13 is an elevational view of the top of an embodiment of the retraction lever;

Fig. 14 is an elevational view of the side of the retraction lever depicted in Fig. 13;

Fig. 15 is an elevational view of the front of the head unload arm used in the preferred embodiment of the present invention;

Fig. 16 is an elevational view depicting the top of the head unload arm depicted in Fig. 15;

Fig. 17 is an elevational view of the right end of the head unload arm depicted in Fig. 15; Fig. 18 is an elevational view of the top of the retraction lever lock;

Fig. 19 is a cross-sectional view of the retraction lever lock depicted in Fig. 18;

Fig. 20 is an elevational view of the bottom of the retraction lever lock depicted in Figs. 18 and 19; Fig. 21 is an elevational view of the side of the head unload assembly base in the direction referenced in Fig. 1;

Fig. 22 is an elevational view of the top of the head unload arm guide;

Fig. 23 is an elevational view of the end of the head unload arm guide depicted in Fig. 22;

Fig. 24 is an elevational view of the side of the solenoid from the direction referenced in Fig. 1; Fig. 25 is the loading algorithm;

Fig. 26 is a representation of the current applied to the voice coil motor (VCM) during the dithering stage of VCM operation;

Fig. 27 is a representation of the current applied to the VCM during the ramp-up stage of VCM operation.

Fig. 28 is an elevational view of the top of a preferred embodiment of the retraction lever;

Fig. 29 is an elevational view of the side of the retraction lever depicted in Fig. 28; and Figs. 30-35 are perspective views of other alternative embodiments of the retraction lever.

Description of the Preferred Embodiment

In accordance with the present invention, a disk drive apparatus is provided for launching read-write heads onto disks and for retracting the read-write heads off of disks. In the preferred embodiment, one disk is contained within a cartridge. The invention is not, however, so limited and may be applied to multiple disks and to disks not mounted in cartridges. In the following description, when a component "A" is described as being on top of a component "B" that means component "A" is further away (in a direction out of the page in Figs. 1-8) from the drive base 10 (i.e., the bottom of the inside of the drive) than component "B" . Referring first to Figs. 1-8, the disk drive apparatus of the instant invention includes the following components. A head arm frame 13 is mounted to the drive base 10. A voice coil motor (VCM) or head-arm-assembly- positioning motor is indicated generally at 16. A head arm assembly 19 is pivotally mounted to the head arm frame 13 for rotation about an axis 22. An inner crash stop 25 is mounted to the voice coil motor 16 and is positioned such that the stop pin bumper 28, which is made of energy absorbing rubber and is mounted on the base end 31 of the head arm assembly 19, impacts the stop pin 34 of the inner crash stop 25 when the head arm assembly 19 is rotated to its innermost position over the media 37. In this preferred embodiment, the stop pin 34 is threaded so that the location where it impacts the stop pin bumper 28 may be adjusted. Head arm assembly 19 comprises a bifurcated load beam 40, including an upper load beam 43 and a lower load beam 46 (Fig. 10) . The head arm assembly 19 further comprises an upper flexure 49 attached to the upper load beam 43, and a lower flexure 52 attached to the lower load beam 46. A pair of transducers (read-write heads) 55, 58 are mounted on the free ends of the flexures 49, 52. The upper read-write head 55 is attached by a gimble (not shown) to the upper flexure 49. The lower read-write head 58 is attached by a gimble (not shown) to the lower flexure 52. These features of the head arm assembly 19 are seen to best advantage in Fig. 10. In this preferred embodiment, a pressing surface 61 comprises part of a molded ratchet 64 mounted below the head arm assembly 19 for rotation therewith. The teeth 67 depicted on the ratchet 64 are not used in this preferred embodiment.

Referring next to Figs. 1-8, 11, and 12, a retraction spring and retraction spring hook will be described. The retraction spring hook 70 is mounted to the drive base 10 adjacent to the area of motion of the ratchet 64. The retraction spring hook 70 has a slot 73 formed therein for adjusting the initial tension in the retraction spring 76. In the preferred embodiment of the present invention, retraction spring 76 has a spring rate of 16 ounces/inch. To adjust the initial tension in the retraction spring 76, one may rotate the retraction spring hook 70 about a mounting screw 79. A second mounting screw 82 rides in the slot 73, thereby limiting the range of motion of the retraction spring hook 70. once the initial tension in the retraction spring 76 has been adjusted, the retraction spring hook 70 is fixed to the drive base 10 by tightening mounting screws 79 and 82. The retraction spring hook 70 includes an upright portion 85 having a spring-retaining groove 88 formed therein (Fig. 12) .

Referring next to Figs. 1-8, 13, 14 and 28-35, the retraction lever 91 will be described. Retraction lever 91 is rotatably mounted to the drive base 10 for rotation about an axis 94. The retraction lever 91 is mounted on its axis 94 below the head arm assembly 19. This is indicated in Figs. 1-8 by depicting the hidden portions of the retraction lever 91 in phantom when they are covered by the head arm assembly 19. Retraction lever 91 includes a pressing end 97. The pressing end 97 of the retraction lever 91 impacts the pressing surface 61 of the ratchet 64 at various times during the operation of the disk drive.

In a preferred embodiment of the present invention, as shown in Figures 28 and 29, the pressing end 97 of the retraction lever 91 is tapered. The portion of the pressing end 97 which impacts the pressing surface 61 of the head arm assembly 19 is narrower than the base of the pressing end. Thus, although the tapered retraction lever 91 is dimensionally stable, it provides some resiliency when the pressing end 97 of the retraction lever 91 collides with the pressing surface 61 of the head arm assembly 19 in order to drive the upper and lower flexures 49, 52 onto the upper and lower guiding surfaces 103, 106 of the forked portion 109 of the head unload arm 112. It is always important to keep the read-write heads 55, 58 from crashing into the media 37, particularly when the media exhibits a high data density. The tapered configuration of retraction lever 91 absorbs a sufficient amount of the energy and shock created by the collision of the pressing end 97 and the pressing surface 61, thereby mitigating any tendency of the read-write heads 55, 58 to crash against the disk 37 when the pressing end 97 impacts the pressing surface 61. The tapered retraction lever 91 is a unitary part that can be molded inexpensively out of a suitable engineering plastic or other structural material. Other alternative embodiments of the retraction lever 91 may serve to mitigate any tendency of the read-write heads 55, 58 to crash against the disk 37 when the pressing end 97 impacts the pressing surface 61.

For example, the alternative embodiment of the retraction lever, as illustrated in Figures 1-8, 10, 13 and 14, envisions a sleeve of damping material 100 (e.g., energy absorbing rubber) mounted on the pressing end 97 of the retraction lever 91.

Figures 30-35 depict the perspective views of other embodiments of retraction lever 91. Figure 30 illustrates an embodiment of the retraction lever 91 wherein the pressing end 97 of the retraction lever 91 is comprised of a metal wire spring 200 that is partially embedded into the retraction lever 91. This metal spring 200 could also be configured as a metal leaf spring 201, as shown in Figure 31. The metal springs 200, 201 are made of a suitable material which provides both dimensional stability and resiliency. Optionally, an energy absorbing material may be placed adjacent to the metal springs. Figure 32 depicts yet another embodiment of the retraction lever 91, the embodiment having a narrow pressing end 97 and a damping material portion 202 fabricated from, e.g., energy absorbing rubber. The side of the pressing end 97 which collides with pressing surface 61 is molded as a unitary structure with the retraction lever 91. Resiliency is provided by the narrowing of the pressing end 97 and the damping material portion 202.

Figure 33 illustrates still another embodiment of the retraction lever 91, wherein the side walls 203a, 203b of the pressing end 97 are thin and the gap 204 between the side walls 203a, 203b are filled with a damping material; the damping material need not fill the entire gap 204. Optionally, the side wall 203a which impacts the pressing surface 61 may be replaced by a metal spring and a damping material then inserted in between the metal spring side wall 203a and the other side wall 203b.

Figure 34 depicts another embodiment of the retraction lever 91, the embodiment having a notch 205 in the pressing end 97. The notch 205 is formed on the side of the pressing end 97 opposite of the side of pressing end 97 which collides with pressing surface 61, and enhances the resiliency of the pressing end 97.

Referring now to Figure 35, another embodiment of the retraction lever 91 is depicted. Pressing end 97 of the retraction lever 91 has a gap 206 formed by a thin periphery of the pressing end walls 208, again enhancing the resiliency of the pressing end 97. Optionally, the gap 206 may be filled with a damping material.

The tapered retraction lever 91, shown in Figure 28, is the preferred embodiment for a number of reasons. First, the tapered retraction lever provides the best balance of dimensional stability and resiliency, yet can be manufactured as a single molded part and is therefore less expensive and simpler to manufacture than embodiments requiring the coupling of two parts. Second, as compared to embodiments utilizing energy absorbing material, the tapered retraction lever is less susceptible to performance changes across a temperature range and provides a more durable wear surface. The tapered retraction lever also advantageously does not require any lubrication between the pressing end 97 and the pressing surface 61. Retraction lever 91 also has a trappable end 115. This trappable end 115 is locked or retained by the retraction lever lock 118 during normal operation of the disk drive. The retraction lever lock 118 is described more fully below and may be seen to best advantage in Figs. 18-20. The trappable end 115 of the retraction lever 91 has a sloped surface 121, which facilitates the trapping action as further described below.

During a portion of the operation of the head launching apparatus of the instant invention, the retraction lever lock 118 presses against a wing 124 comprising part of the retraction lever 91. Specifically, a push pin 127 mounted to the bottom surface 130 of the retraction lever lock 118 may impact the wing 124 upon rotation of the retraction lever lock 118 depending upon the degree of rotation of the retraction lever 91. In particular, during the initial portion of the head-loading operation of the drive (Fig. 2) , the push pin 127 rotates the retraction lever 91 to create a gap between the pressing end 97 of the retraction lever 91 and the pressing surface 61 of the ratchet 64. The head-loading operation of the drive is discussed more fully below. The retraction lever 91 includes a hole 133, which serves as an attachment point for the retraction spring 76. The head unload arm 112 is described further below and may be seen to best advantage in Figs. 9, 10, and 15-17.

Details concerning the components attached to the head load assembly base 136 will now be provided. Integrally formed with the head load assembly base 136 is an upward projection 139. This upward projection 139 may be seen to best advantage in Fig. 21. Fig. 21 depicts an elevational view of the end of the head load assembly base 136 in' the direction indicated by reference numeral 21 in Fig. 1. The upward projection 139 acts as a stop for the head unload arm 112. The upward projection 139 thereby limits the most rearward travel of the head unload arm 112 as discussed more fully below. A first pin 142 and a second pin 145 are also mounted in the head load assembly base 136. The first pin 142 acts as the axis of rotation for the retraction lever lock 118 and the head unload arm 112. The second pin 145 rides in a curved port 148 during rotation of the retraction lever lock 118. The curved port 148 thereby limits the range of permissible rotation of the retraction lever lock 118. The retraction lever lock is depicted to best advantage in Figs. 18-20.

The retraction lever lock 118 is also connected to the solenoid 151. The solenoid 151, which may be seen in Figs. 1-8 and 24, is characterized by a spring return to the de-energized position. That is, when power to the solenoid 151 is turned off, the central shaft or plunger 154 of the solenoid 151 extends fully to its de-energized position. Fig. 24 represents a side view of the solenoid 151 from the direction indicated by reference number 24 in Fig. 1. The retraction lever lock 118 is swingably connected to the plunger 154 of the solenoid 151 with a connecting pin 157 (Fig. 24) . The solenoid 151 generates the force that rotatably positions the retraction lever lock 118. The solenoid 151 thus activates the drive retraction lever locking mechanism, which stores the mechanical energy that facilitates automatic retraction of the read-write heads 55, 58 when power is taken away from the disk drive. The retraction lever lock 118 also includes a trap pin 160. The trap pin 160 projects from the bottom surface 130 of the retraction lever lock 118. This pin 160 is used to trap the trappable end 115 of the retraction lever 91 as further described below. Figs. 7 and 8 depict the trap pin 160 performing its trapping function.

Referring now to Figs. 9, 10, and 15-17, the head unload arm 112 will be described. The head unload arm 112, which may be manufactured from a suitable engineering plastic or other structural material, is mounted on top of the retraction lever lock 118 for rotation about the first pin 142 (pin 142 is depicted, for example, in Figs. 1-8 and 21) . In the preferred embodiment of the present invention, the material between the upper and lower guiding surfaces 103, 106 of head unload arm 112 has been removed to accommodate a disk 37 when it has been loaded into the drive. This may be seen to best advantage in Fig. 9. The head unload arm 112 thus includes a forked portion 109. As may best be seen in Figs. 9 and 10, each guiding surface 103, 106 of the forked portion 109 of the head unload arm 112 has the shape of a flat-taper ramp, with a knee between each ramped or tapered portion and its respective flat portion. Referring to Fig. 9 in particular, upper guiding surface 103 comprises ramped portion 104 and flat portion 105 separated by an upper knee 169. Similarly, lower guiding surface 106 comprises ramped portion 107 and flat portion 108 separated by a lower knee 170. This flat-tapered designed effectively lifts each read-write head 55, 58 from its operational position near the disk surface to its retracted position safely away from the disk surface. When the head arm assembly 19 is fully retracted, the upper and lower flexures 49, 52 of head arm assembly 19 are driven onto the upper and lower flat portions 105, 108, respectively. The flat portions 105, 108 help minimize the vertical motion of the flexures 49, 52 so that a cartridge may be loaded and also provide surfaces parallel to the plane of the flexures 49, 52 to minimize pressure upon the guiding surfaces 103, 106 when the read-write heads 55, 58 are fully parked on the flat portions 105, 108. The head unload arm 112 also includes a downward projection 163 and a bumper mount 166.

During any rotation of the head unload arm 112, the free end of the head unload arm 112 slidably rests on a head unload arm guide 172. This head unload arm guide 172, which like the head unload arm itself may be manufactured from a suitable material such as plastic, is depicted in Figs. 1-8, 10, 22, and 23. The guide 172 is rigidly mounted to the head load assembly base 136. A coil spring 175 (Fig. 10) biases the downward projection 163 of the head unload arm 112 against the stopping surface 178 of the head unload arm guide 172. The coil spring 175 is mounted around the first pin 142, between the head unload arm 112 and the retraction lever lock 118. The distance between the stopping surface 178 of the head unload arm guide 172 and the upright projection 139 defines the full range of possible positions for the head unload arm 112. A bumper 181 of energy absorbing material (e.g., energy-absorbing rubber) is mounted around the bumper mount 166. The bumper 181 is cylindrically shaped in the preferred embodiment, and helps mitigate any tendencies of the head arm assembly 19 to rebound when the read-write heads 55, 58 are retracted from the surface of the disk 37. The coil spring 175 further helps dampen the impact between the head arm assembly 19 and the head unload arm 112. The coil spring 175 and the bumper 181 mitigate any high-speed rebound problems occurring when the head arm assembly 19 is traveling to its retracted position under the influence of the retraction spring 76.

Figures 1-8 are arranged to show the progression of the head launch sequence, starting with a drive that has not yet been powered up (Fig. 1) and ending with a drive that has successfully launched the read-write heads 55, 58, achieving operational status. In the disclosed invention, one mechanism is used to both launch and later to retract the read-write heads 55, 58. The launch sequence will be described first. During the head launch sequence, the heads 55, 58 are positioned without position or velocity feedback. In other words, the instant invention describes an open-loop system. During launch, a primary concern is to control the velocity of the upper and lower flexures 49, 52 as they leave their respective guiding surfaces 103, 106 so as to prevent the heads 55, 58 from crashing into the media 37. As the upper and lower flexures 49, 52 move along their respective guiding surfaces 103, 106, the resultant force acting on the head arm assembly 19 changes, particularly as the upper and lower flexures 49, 52 transition from the flat portions 105, 108 to the tapered portions 104, 107 of the upper and lower guiding surfaces 103, 106. As may be appreciated from considering Figs. 9 and 10, the read-write heads 55, 58 travel toward each other and the media 37 as the flexures 49, 52 slide down the guiding surfaces 103, 106. If the heads 55, 58 approach each other too quickly as they travel down their respective guiding surfaces 103, 106, the heads 55, 58 will crash into the media 37 upon leaving the head unload arm 112. If the read-write heads 55, 58 crash into the media 37, they can be damaged or data stored on the media 37 can be destroyed, particularly with high-density media 37. If, on the other hand, the read-write heads 55, 58 are traveling toward the media 37 too slowly as they leave the guiding surfaces 103, 106, of the head unload arm 112, the heads 55, 58 will not come off of the head unload arm 112 cleanly, and their transition to flight over the media

37 will be corrupted. This corruption is more likely in a removable media device due to the increased vertical runout inherent in the interchange of media.

Referring now to Figs. 1-8 and 25-27, the step-by-step launching process will be described. Fig. 25 presents the algorithm for this process, wherein the values given are DAC constants. Figs. 26 and 27 show the current flow through the VCM during a portion of the launching process. In the preferred embodiment of the present invention, a neutral VCM has an 8OH DAC value. Values greater than 8OH apply force toward the inside diameter or "ID." Values less than 80H apply force toward the outside diameter or "OD." The torque per DAC count is 7.32xl0^"3 inch-ounce. Fig. 1 depicts the launching and retracting apparatus of the instant invention with a cartridge inserted in the drive. Upon command, the media 37 spins up. The launch sequence is initiated when the media 37 reaches a specified rotational speed.

First, as depicted in Fig. 1, an OD force is generated to move the flexures 49, 52 to the top of the ramped portions 104, 107 of the upper and lower guiding surfaces

103, 106, respectively (step 1 in Fig. 25) . Then, as depicted in Fig. 2, the solenoid 151 is activated (step 2 in Fig. 25) . When the solenoid 151 is activated, the plunger 154 is retracted into the solenoid 151. As the plunger 154 retracts, it pulls on the retraction lever lock 118, thereby slightly rotating the retraction lever lock 118 in a first direction (counterclockwise in Fig. 2) . This rotation forces the push pin 127 against the wing 124 of the retraction lever 91. The force thus generated on the wing 124 causes the retraction lever 91 to rotate slightly about the axis 94 (clockwise in Fig. 2) . This latter rotation of the retraction lever 91 creates a gap between the pressing end 97 of the retraction lever 91 and the pressing surface 61 of the molded ratchet 64.

The current in the voice coil motor 16 is then dithered (step 3 in Fig. 25; see also Fig. 26) to break any stiction between the flexures 49, 52 and the flat portions 105, 108 of the head unload arm 112, without excessively accelerating the flexures 49, 52 across the flat portions 105, 108. This dithering generates a net force that rotates the head arm assembly counterclockwise in Fig. 2 until contact is reestablished between the pressing end 97 of the retraction lever 91 and the pressing surface 61. This places the apparatus in the position depicted in Fig. 3 without a gap between the retraction lever 91 and the pressing surface 61.

At this point, the upper and lower flexures 49, 52 have transitioned the respective knees 169, 170 of the upper and lower guiding surfaces 103, 106 (Figs. 3 and 9) . The flexures 49, 52 are resting on the ramped portions

104, 107, respectively, of the head unload arm 112 at a "pause point" or pre-loading position. At this pre¬ loading position, the spring force generated by the retraction spring 76 (as determined by the position of the retraction lever 91, which is being rotated by the push pin 127 of the retraction lever lock 118, which is in turn being rotated by the solenoid 151 as described above) is greater than the net dithering torque generated by voice coil motor 16, so the flexures 49, 52 do not move off of the pre-loading position (although there may be some minor dithering motion about the preloading position) . Therefore, the location of the pre-loading position is determined by the position of the retraction lever 91, which in turn depends upon the settings of the solenoid 151. The solenoid 151 is adjusted such that the pre- loading position occurs just after the flexures 49, 52 are beyond the knee 169, 170 (Figs. 3 and 9) . The duration of the dithering (presently this is approximately 1.4 seconds) is established so that in the worst case (sticky friction) , the flexures 49, 52 will arrive at the pre- loading position before the dithering stops.

Fig. 9 depicts an enlarged view showing the upper and lower flexures 49, 52 at this pre-loading position. In Fig. 9, one may clearly see the position of the flexures 49, 52 on the ramped portions 104, 107 of the upper and lower guiding surfaces 103, 106, respectively. Up to this point, the force generated by the retraction spring 76 on the retraction lever 91 has been balanced by the force generated by the solenoid 151 on the wing 124 via the push pin 127 of the retraction lever lock 118. After contact has been reestablished between the pressing end 97 of the retraction lever 91 and the pressing surface 61, the voice coil motor 16 begins to "take over" from the solenoid 151 the job of countering the force being generated by the stretched retraction spring 76. The head arm assembly 19, through the pressing surface 61 of the molded ratchet 64, engages the retraction lever 91 and counters the force produced by the retraction spring 76. As the voice coil motor 16 is further energized, the head arm assembly 19, through the pressing surface 61 of the molded ratchet 64 pushes the retraction lever 91 and stretches the retraction spring 76. The emf in the voice coil motor 16 is incrementally increased through firmware so that the upper and lower flexures 49, 52 begin to move on the ramped portions 104, 107 of the guiding surfaces 103, 106 of the head unload arm 112. The emf in the voice coil motor 16 is controllably increased or ramped up at a fixed rate of change, using techniques that would be apparent to anyone of ordinary skill in the art (see, e.g., step 4 in Fig. 25; see also Fig. 27) . This ramp-up of the emf in the voice coil motor causes the retraction spring 76 to stretch until it equalizes the force produced by the motor 16. The head arm assembly 19 in turn moves at a controlled speed--equivalent to D'Arsonval movement--along the ramped or sloped portions 104, 107 of the guiding surfaces 103, 106 and out over the disk surface. If the voice coil motor was simply energized from a fully parked position and rotated to move the flexures directly over the knee and down the ramp portions of the head unload arm, without stopping at the pre-loading position, control over the velocity of the heads would be much more difficult to achieve. This is because application of force sufficient to overcome friction and stiction between the flexures and the head unload arm guiding surfaces, coupled with the unknown loading dynamics caused by the flexures going over the knees of the head unload arm, would lead to acceleration of the flexures and loss of velocity control . By starting the voice coil motor current ramp-up after the flexures have reached the pre-loading position, however, and thereafter controlling the current in the voice coil motor 16, the drive regulates the translational velocity of the read¬ write heads 55, 58 as the upper and lower flexures 49, 52 leave the upper and lower guiding surfaces 103, 106 of head unload arm 112. In this manner, as the read-write heads 55, 58 transition from resting on the forked portion 109 of the head unload arm 112 to "flying" over the spinning media 37, the velocity of the read-write heads 55, 58 is controlled as the heads approach each other and their respective disk surfaces.

During the loading process, the firmware in the microprocessor of the disk drive's electronic circuits looks for servo data that it expects to find on the media 37 (step 4 in Fig. 25) . If the read-write heads 55, 58 begin to read servo data from the disk, they probably have been fully loaded. Up to a twelve-step ramp-up of the voice coil motor 16 is used in the preferred embodiment

(step 4 in Fig. 25; see also Fig. 27), but the system is normally adjusted so that the heads 55, 58 should be off of the head unload arm 112 after the sixth ramp-up step. To ensure that the read-write heads 55, 58 have actually cleared the head unload arm 112, the disk drive firmware continues to drive the flexures 49, 52 from the head unload arm 112 after the read-write heads 55, 58 begin to read servo data from the disk (see step 5 in Fig. 25) . This occurs even though the flexures 49, 52 may have fully cleared the head unload arm 112 as soon as the read-write heads 55, 58 began to read servo data. Next, the solenoid 151 is de-activated (step 6 in Fig. 25) , and its plunger 154 returns to its extended position (Fig. 4) . When the plunger 154 returns to its extended position, the retraction lever lock 118 is rotated in a second direction (clockwise in Fig. 4) to a position that permits the trappable end 115 of the retraction lever 91 to eventually be rotated into a position to be trapped or locked by the trap pin 160 of the retraction lever lock 118. This trapping action is more fully described below with reference to Figs. 6 and 7. The current to the voice coil motor 16 is then further increased (step 7 in Fig. 25) . Increasing the current to the voice coil motor 16 forces the head arm assembly 19 to make an initial run from the outer track of the media 37 to the innermost track (see, e.g., Fig. 5) . Fig. 6 depicts the head arm assembly 19 positioned beyond the inner-most track. When the head arm assembly 19 is thus positioned, the stop pin bumper 28 of energy absorbing material has impacted the stop pin 34. Also, when the head arm assembly 19 is at this position, the retraction spring 76 is at its maximum elongation, and the head arm assembly 19 has "cocked" the retraction lever 91, which is now "trappable" by the retraction lever lock 118. This initial run of the head arm assembly 19 from the outer track to the inner-most track of the media 37 increases the potential energy in the retraction spring 76, thus enabling the drive's automatic-head-retraction system, while placing the retraction lever 91 in "locking position" so that the spring energy may be "stored" by the retraction lever lock 118.

After a short delay (step 8 in Fig. 25) , the solenoid 151 is again activated as depicted in Fig. 7. When the solenoid 151 is energized, the plunger 154 is drawn leftward in Fig. 7. This action rotates the retraction lever lock 118 in the first direction

(counterclockwise in Fig. 7) to lock the retraction lever

91 in place. When the retraction lever 91 is positioned as shown in Fig. 7, and the solenoid 151 is energized, the retraction lever lock 118 traps the trappable end 115 of the retraction lever 91 behind the trap pin 160 attached to the bottom of the retraction lever lock 118, thereby holding the retraction spring 76 in a stretched configuration and storing the spring's potential energy. In particular, the trap pin 160, which may be seen to best advantage in Figs. 18-20, presses against the sloped surface 121 of the trappable end 115 of the retraction lever 91. This configuration, wherein the trap pin 160 has the retraction lever 91 trapped, may be seen in Figs. 7 and 8. As long as the solenoid 151 is activated, the retraction lever 91 is held in a spring-loaded state. As seen in Fig. 8, when the retraction lever 91 is locked by the retraction lever lock 118, the retraction spring 76 no longer influences the motion of the head arm assembly 19. The pressing end 97 of the retraction lever 91 is not touching the pressing surface 61 of the molded ratchet 64, and the head arm assembly 19 can move freely over the media 37. The drive next goes into a calibration routine, which makes the drive ready to accept a command from a host computer and to perform any requested read- write operations.

The retraction system of the instant invention is capable of retracting the read-write heads 55, 58 under normal conditions as well as under failure or loss of power conditions. During a normal retraction operation, the operator typically initiates the retraction sequence by pressing a button on the front of the disk drive. Alternatively, the sequence may be initiated through a sequence of interface commands. After initiation of the sequence, the read-write heads 55, 58 seek to the outer track. Then, the voice coil motor 16 provides sufficient force (6OH DAC in the preferred embodiment) to lift or push the read-write heads 55, 58 up the ramped portions 104, 107 (Fig. 9) of the guiding surfaces 103, 106 of the head unload arm 112 to a retracted location. The drive then spins down, and the solenoid 151 is subsequently de¬ activated, whereby the plunger 154 is driven rightward in Figs. 1-8. As the plunger 154 travels rightward, the retraction lever lock 118 is rotated in the second direction (clockwise in Fig. 8) . When the retraction lever lock 118 thus releases the trappable end 115 of the retraction lever 91, the pressing end 97 of the retraction lever 91 is forced against the pressing surface 61. The retraction spring 76 thereby helps hold the read-write heads 55, 58 on the head unload arm 112 while, for example, a cartridge is removed from the drive. In a fixed drive, this feature may be engaged, for example, before the drive or the system containing it is moved. The following paragraphs describe retraction of the read-write head 55, 58 when the drive experiences an unexpected power loss. In this situation, the drive's automatic-headretraction system becomes operational. The energy that will be used for unloading the read-write heads 55, 58 in this situation is the energy stored in the stretched retraction spring 76.

In the instant invention, before a power loss occurs, the retraction lever lock 118 prevents the retraction lever 91 from influencing the operational movement of the head arm assembly 19. This locking action is fully described above. As is well known in the art, the head arm assembly 19 can then be used to access data from tracks on the media 37. When power is unexpectedly removed from the drive, the solenoid 151 eventually relaxes, releasing its plunger 154. The released plunger 154 travels rightward in Figs. 7 and 8, which rotates the retraction lever lock 118 in the second direction (clockwise in Figs. 1-8) . With the retraction lever lock 118 thus rotated, trap pin 160 can no longer retain the trappable end 115 of the retraction lever 91. The stored energy of the retraction spring 76 is consequently released. The released spring energy is applied to the retraction lever 91 at the hole 133 in the retraction lever 91 where the retraction spring 76 is attached to the retraction lever 91. This in turn causes the retraction lever 91 to rotate counterclockwise in Figs. 1-8, eventually establishing contact between the pressing end 97 of the retraction lever 91 and the pressing surface 61 of the ratchet 64. The force against the pressing surface 61 by the pressing end 97 rotates the head arm assembly 19 clockwise in Figs. 1-8 and drives the head arm assembly 19 onto the head unload arm 112 by pushing the upper and lower flexures 49, 52 up the upper and lower guiding surfaces 103, 106, respectively. In this manner, the apparatus retracts the read-write heads 55, 58 independent of the location of the head arm assembly 19 over the media 37 when the drive losses power, placing the read-write heads 55, 58 safely away from the media 37.

When the head arm assembly 19 is near the outer track of the media 37 as depicted in Fig. 8, the gap between the pressing end 97 of the retraction lever 91 and the pressing surface 61 of the molded ratchet 64 is greatest. If the drive experiences an unexpected loss of power when the head arm assembly 19 is so positioned, the pressing end 97 has its greatest distance within which to accelerate towards the pressing surface 61. In this situation, the sleeve of damping material 100 helps mitigate any potential for rebound of the retraction lever 91 after its pressing end 97 impacts the pressing surface 61. As an alternative to the sleeve 100, the retraction lever 91 itself may be constructed from a material or in a shape that mitigates any potential for rebound. For example, the retraction lever 91 itself could be formed from resilient material that would give rather than bounce when the pressing end 97 impacts the pressing surface 61. In the preferred embodiment of the retraction lever 91, as shown in Figures 28 and 29, the retraction lever 91 has a tapered pressing end 97.

The above-described invention provides many advantages over the prior art, including the following. It keeps the read-write heads 55, 58 off of the media 37 any time the disk drive is without power, since the heads 55, 58 are always retracted from the media 37 using mechanical energy whenever the drive experiences a loss of power. Because the read-write heads 55, 58 are kept away from the disk surface when the disk drive is not powered, damage to the read-write heads 55, 58 is much less likely to occur during transportation of the drive with a disk loaded. The invention launches the read-write heads 55, 58 without employing devices like damping pots and tachometers or other velocity sensors. The absence of these devices makes the drive less complex and less expense to build, while increasing the reliability of the drive. While what has been described above is a preferred embodiment of this invention, it will be obvious to those skilled in the art that numerous changes may be made without departing from the spirit or scope of the invention. For example, a linear actuator may be used in place of the voice coil motor used in the preferred embodiment. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as being illustrative only and not limiting. The invention, therefore, is not to be limited except in accordance with the below claims.

Claims

1. An apparatus for retracting a head arm assembly in a disk drive, the disk drive including at least one disk and at least one read-write head attached to the head arm assembly, the head arm assembly having associated therewith a first surface, said apparatus comprising: a retraction lever having a tapered pressing end, wherein said retraction lever is positioned such that said pressing end impacts the first surface of the head arm assembly during retraction of the head arm assembly to a position in which the read-write head is outside the perimeter of the disk; a biasing member that mechanically biases said pressing end of said retraction lever toward the first surface of the head arm assembly; and a retraction lever lock positioned to alternatively trap and release said retraction lever.

2. An apparatus for retracting a head arm assembly in a disk drive, the disk drive including at least one disk and at least one read-write head attached to the head arm assembly, the head arm assembly having associated therewith a first surface, said apparatus comprising: a retraction lever having a pressing end, wherein said pressing end comprises a spring and said retraction lever is positioned such that said pressing end impacts the first surface of the head arm assembly during retraction of the head arm assembly to a position in which the read¬ write head is outside the perimeter of the disk; a biasing member that mechanically biases said pressing end of said retraction lever toward the first surface of the head arm assembly; and a retraction lever lock positioned to alternatively trap and release said retraction lever.

3. An apparatus for retracting a head arm assembly in a disk drive, the disk drive including at least one disk and at least one read-write head attached to the head arm assembly, the head arm assembly having associated therewith a first surface, said apparatus comprising: a retraction lever having a pressing end with a notch, wherein said retraction lever is positioned such that said pressing end impacts the first surface of the head arm assembly during retraction of the head arm assembly to a position in which the read-write head is outside the perimeter of the disk; a biasing member that mechanically biases said pressing end of said retraction lever toward the first surface of the head arm assembly; and a retraction lever lock positioned to alternatively trap and release said retraction lever.

4. An apparatus for launching and for subsequently retracting a read-write head attached to a head arm assembly, the head arm assembly having a first surface associated therewith, said apparatus comprising: a pivotally-mounted retraction lever having a tapered pressing end and a trappable end, wherein said retraction lever is positioned such that said pressing end is adjacent to the first surface of the head arm assembly; a mechanical biasing member that biases said pressing end toward the first surface of the head arm assembly; a retraction lever lock positioned to alternatively trap and release said trappable end of said retraction lever; a voice coil motor operatively associated with said head arm assembly; and a head unload arm comprising an upper guiding surface and a lower guiding surface, wherein each guiding surface has a flat-taper shape with a knee between a ramped portion and a flat portion.

5. An apparatus for launching and for subsequently retracting a read-write head attached to a head arm assembly, the head arm assembly having a first surface associated therewith, said apparatus comprising: a pivotally-mounted retraction lever having a pressing end and a trappable end, wherein said pressing end comprises a spring and said retraction lever is positioned such that said pressing end is adjacent to the first surface of the head arm assembly; a mechanical biasing member that biases said pressing end toward the first surface of the head arm assembly; a retraction lever lock positioned to alternatively trap and release said trappable end of said retraction lever; a voice coil motor operatively associated with said head arm assembly; and a head unload arm comprising an upper guiding surface and a lower guiding surface, wherein each guiding surface has a flat-taper shape with a knee between a ramped portion and a flat portion.

6. An apparatus for launching and for subsequently retracting a read-write head attached to a head arm assembly, the head arm assembly having a first surface associated therewith, said apparatus comprising: a pivotally-mounted retraction lever having a pressing end with a notch and a trappable end, wherein said retraction lever is positioned such that said pressing end is adjacent to a pressing surface of said head arm assembly; a mechanical biasing member that biases said pressing end toward said pressing surface; a retraction lever lock positioned to alternatively trap and release said trappable end of said retraction lever; a voice coil motor operatively associated with said head arm assembly; and a head unload arm comprising an upper guiding surface and a lower guiding surface, wherein each guiding surface has a flat-taper shape with a knee between a ramped portion and a flat portion.