1.  Field of the Invention
The present invention relates to an optical disk reading device, and in particular, to a collapsible locking mechanism that is more effective in resisting the impact of shock that may be experienced by the optical disk reading device. 
2.  Description of the Prior Art
Optical disk reading devices are becoming increasingly popular as storage media devices.  Optical disk reading devices, such as thin-type CD drives, are low in cost and can store large amounts of data having different contents, including music, video, programs, and information data. 
Weight and space are important considerations in the design of thin-type CD drives.  The biggest challenge is how to fit all the necessary components of the CD drive into a limited space. 
In one attempt to reduce cost and to adapt to the limited space constraints, the conventional motor drive for loading and unloading a compact disk (CD) has been eliminated, and a manual loading and ejection device is used to facilitate the loading and unloading operation.  FIGS.  1-5 illustrate a conventional CD drive and its manual loading and ejection device.  The conventional CD drive has a chassis 1, a tray 2 and a playback unit 3.  The tray 2 and the playback unit 3 are located inside the chassis 1, and the playback unit 3 is positioned above the tray 2, with the tray 2 acting as a supporting device for a CD.  When the tray 2 is ejected, the user can place a CD on the tray 2 and push the tray 2 back into the CD drive.  A locking mechanism 4 then functions to lock the tray 2 to prevent it from being inadvertently ejected when the CD drive is in use. 
The conventional locking mechanism 4 is positioned on the tray 2 and inside the chassis 1.  The conventional locking mechanism 4 is typically made of a solid piece of an inelastic material.  The locking mechanism 4 has an axis 5 that extends through an axle hole 6 on the locking mechanism 4.  A shaft can be retained in the axle hole 6 along the axis 5 and pivotably connects the locking mechanism 4 to the tray 2 so as to define a pivot axis about which the body of the locking mechanism 4 can pivot.  The tray 2 and the locking mechanism 4 carried thereon are adapted to slide in and out of the CD drive along the axis X (see FIGS.  1 and 5). 
A locking member 7 is secured to a fixed location on the chassis 1.  When the tray 2 is pushed into the CD drive, a front end 8 of the locking mechanism 4 will abut the locking member 7, thereby locking the tray 2 inside the CD drive.  To eject the tray 2, the user actuates another element (not shown, but can be a switch or other actuating mechanism) which causes the locking mechanism 4 to rotate about its pivot axis 5 so as to release the engagement between the front end 8 and the locking member 7, so that the locking mechanism 4 can slide past the locking member 7 to allow the tray 2 to be slid out of the CD drive.  The locking mechanism 4 can also be provided with a prod extension 41 adjacent the front end 8 so that the user can use a thin wire or other similar mechanism to push or prod the prod extension 41 to cause the locking mechanism 4 to rotate about its pivot axis 5 so as to release the engagement between the front end 8 and the locking member 7.  Thus, the prod extension 41 functions as an emergency ejection mechanism. 
Unfortunately, when the CD drive is being transported (either by the manufacturer, the retailer or the user) from one location to another, shock and other related forces are inevitable.  In this regard, if the force is exerted in the direction of arrow X in FIGS.  1 and 5 (e.g., if the tray 2 is dropped vertically in the direction of the arrow X), the shock energy of the force will be absorbed by the locking mechanism 4 (that is fixed to the tray 2) and the locking member 7 (that is fixed to the chassis 1), and in particular, the front end 8 and the locking member 7.  It has been noticed that if this force and the resulting shock energy is too large, then the locking mechanism 4 might fracture or break because of the inelastic and solid nature of the body of the locking mechanism 4.  Once the locking mechanism 4 is broken, the tray 2 will slide down, and cannot be locked inside the CD drive, thereby rendering the entire CD drive unusable. 
Thus, there remains a need to provide a locking mechanism that is simple in construction, small in size, and capable of withstanding strong impact forces without experiencing breakage.