GB2170644A - Latch mechanism for movable transducers - Google Patents

Abstract

A latch mechanism for use in a disc drive rotary actuator (10) includes a selectively energizable electromagnet (54) mounted to the actuator (10) and spaced from the magnets of the actuator (18), and a ferrous latch arm (50) pivotally attached between the magnets (18) and the electromagnet (54) whereby the latch arm (50) can assume two stable positions of low magnetic reluctance for stray flux from the magnets (18). In one position the latch arm (50) pivots towards the magnets (18) and engages the rotary actuator at the notch (60). In the other position, the latch arm (50) pivots towards the electromagnet (54) and disengages the rotary actuator. Positioning of the latch arm is dependent on momentary energization and polarity of the electromagnet (54). <IMAGE>

Description

SPECIFICATION Latch mechanism This invention relates to latch mechanisms for use in electromagnetic devices, and more particularly the invention relates to a latch mechanism for use in a disc drive rotary actuator or like device.

Discs having magnetic coatings on the surfaces thereof provide memories for bits of data which can be randomly accessed at high speed for either retrieving or storing data.

Typically, the heads are mounted on support arms with each head having a small pickup coil which is rapidly moved across a disc surface while a disc is spinning for detecting or storing data in concentric data tracks on the disc surface. The heads ride on a thin layer of air created by the spinning disc with the heads being in close proximity to but spaced from the disc surface.

The actuators for the pickup heads can move the head arm assembly linearly across the disc surfaces or rotatably across the disc surfaces. When the disc drive is powered down the pickup heads are moved to an innermost position over a landing area of the disc surface. After power down the carriage assembly is latched with the pickup heads resting on the landing area so that the heads are not inadvertently moved across the disc surface.

Heretofore, latch mechanisms for this purpose have typically comprised a lever mechanism driven by a spring loaded solenoid. If the latch is self-locking, a magnet must be provided within the solenoid to hold the latch in the retracted position. A manually operated latch mechanism is disclosed in US-A 4,331,989.

In accordance with the present invention a latch mechanism, for use in a device having magnet means and a movable member therein, comprisesg a ferrous latch arm for engagement with said movable member, an energizable electromagnet for mounting in said device spaced from said magnet means, means for pivotally attaching said latch arm between said magnet means and said energizable electromagnet whereby said latch arm pivots towards said magnet means and engages said movable means in a first stable low reluctance path and said latch arm pivots towards said electromagnet and disengages said movable means in a second stable low reluctance path, positioning of said latch arm being dependent on energization and polarity of said electromagnet.

The present invention provides a simple latch mechanism which utilizes stray magnetic fields that exist in electromagnetic devices.

The latch arm is made of ferrous material which is pivotally mounted between the magnet means and a selectively energizable electromagnet. The latch provides two paths of low magnetic reluctance for the stray flux emanating from the magnet means. These two paths correspond to two differnt positions of the latch arm. In one position the latch arm pivots towards the magnet means to a stop position, for example, provided by a non-ferrous pin. This position of the latch arm provides a low reluctance magnetic path for stray magnetic flux from the magnet means and also engages and locks the movable member. In the other position the latch arm disengages the movable member and pivots towards the electromagnet to provide a second low reluctance magnetic path.The electromagnet can be momentarily energized to cause the latch arm to pivot from one position to the other, the polarity of the electromagnet determining the direction of latch arm movement.

The latch mechanism of the invention has been implemented in a disc drive rotary actuator, and the invention will be described with reference thereto. However, the latch mechanism of the invention has applications in other electromagnet devices.

An example of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a rotary actuator. and disc drive including a latch mechanism in accordance with the invention.

Figure 2 is a top plan view partially in section illustrating the latch mechanism of Fig. 1 in a locked position and in an unlocked position.

Figure 3A is a top plan view of the latch mechanism of Fig. 2 in the locked position illustrating the magnetic flux pattern.

Figure 3B is a top plan view of the latch mechanism of Fig. 2 in the unlocked position illustrating the magnetic flux pattern.

Referring now to the drawings, Fig. 1 is a perspective view of a rotary actuator shown generally at 10 for accessing and storing data on a plurlaity of discs 12 mounted on a spindle 14. The rotary actuator 10 includes a first magnet structure 16 which accommodates magnets 18 and a second magnet structure 20 which supports magnets 22. The magnet structures preferably comprise two ferrous pieces which are welded and brazed together to form a unitary structure. Alternatively, the support structure can be investment cast of a single piece.

The magnet structure supports a pivot block assembly which is illustrated in Fig. 1 and in the top plan view partially in section of Fig. 2.

The pivot block 30 fits over and is fastened to a bearing support shaft 32 which is mounted to bearings in the support structure.

The head arms 34 preferably fit into dovetail slots 36 on one side of the pivot block. On the opposite side of the block 30 is a coil holder 38 in which a coil 40 is mounted by suitable means such as epoxy. Coil holder 38 is preferably a separate piece which is fastened to the pivot block by means of bolts 42. The coil 40 is flat and is suiable for a low profile drive.

Mounted to one end of the arms 34 are pickup head assemblies 44. In Fig. 2 the support arms 34 and head assemblies 44 are shown in an innermost position with the pickup heads 46 at an innermost position over a landing area 47 of the disc surface. The outermost position of the head arms and pickup heads is illustrated by dotted lines.

A latch mechanism including a ferrous arm 50 pivoted to the support structure by a nonferrous pin 52 is positioned between the magnets of the disc drive and an electromagnet 54 having electrical leads 55 and a ferrous arm 56 projecting therefrom. The arm 50 provides two paths of low magnet reluctance for the stray magnet flux from the magnets. In a first position, arm 50 pivots towards magnet 18 and engages a non-ferrous pin 58 tq provide a low reluctance path from the magnet through arm 50 to the support structure 16.

In the second position, the arm 50 pivots into engagement with arm 56 to provide a low reluctance path from the magnet 18 through arms 50 and 56 and electromagnet 54 to the support structure 16.

The arm 50 assumes one of the two positions upon the momentary energization of the electromagnet 54. Arm 50 moves from the first position to the second position engaging arm 56 when the electromagnet produces flux to magnetically attract arm 50. Arm 50 moves back to the first position when the electromagnet 54 is momentarily enegized to produce flux in a direction opposing the flow of leakage flux through arm 56 and electromagnet 54. Arm 50 then pivots back to the first position engaging the pin 58. Both of the two positions are stable positions and the arm 50 will tend to stay in either position in the absence of a momentary energization of electromagnet 54.

As further shown in Fig. 3A, the rotary actuator 30 includes a notch 60 which receives the pivot arm 50 when the rotary actuator moves the heads to the landing position for power down and locking of the actuator and arm 50 is pivoted to engage pin 58. Accordingly, the arm 50 engaging the notch 60 maintains the rotary actuator in a locked position with the pickup heads on the landing surface of the disc.

To unlock the latch mechanism, the electromagnet 54 is momentarily energized with the resulting flux being in the same direction as the stray flux and the arm 50 pivots to abut the arm 56 as shown in Fig. 3B. In this position the arm 50 assumes a position of low magnetic reluctance for the stray flux 64, which can easily pass through the arm 56 and the electromagnet 54 and return to the magnet through the support structure 16. Arm 50 remains in this position until electromagnet 50 is momentarily energized to produce flux opposing the above described flux path whereupon arm 50 pivots back into engagement with pin 58.

The latch mechanism in accordance with the invention is simple in structure yet has proved efficient in operation in a disc drive. Further, the elimination of a solenoid and its sliding surface eliminates contamination problems.

Features of the disc drive rotary actuator are also described and claimed in U.K. Applications Nos. 8601749, 8601750, and 8601751.

Claims (5)

1. A latch mechanism, for use in a device having magnet means and a movable member therein, comprising a ferrous latch arm for engagement with said movable member, an energizable electromagnet for mounting in said device spaced from said magnet means, means for pivotally attaching said latch arm between said magnet means and said energizable electromagnet whereby said latch arm pivots towards said magnet means and engages said movable means in a first stable low reluctance path and said latch arm pivots towards said electromagnet and disengages said movable means in a second stable low reluctance path, positioning of said latch arm being dependent on energization and polarity of said electromagnet.

Q A latch mechanism as claimed in Claim 1, including means for limiting travel of said latch arm towards said magnet means.

3. A latch mechanism as claimed in Claim 1 or Claim 2, wherein said electromagnet includes a ferrous arm extending therefrom which is engaged by said latch arm when said latch arm pivots towards said electromagnet.

4. A disc drive rotary actuator comprising a support structure for supporting a plurality of magnets in spaced relationship, a plurality of magnets mounted to said support structure, shaft means supported by and rotatable in said support structure, a pivot block assembly mounted on said shaft means for rotation therewith, and a latch mechanism as claimed in any preceding claim, said magnets constituting said magnet means and said pivot block assembly constituting said movable member.

5. A latch mechanism substantially as herein described with reference to the accompanying drawings.