You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     The present invention relates to a card-operated lock, and in particular to a lock using a card with embossed letters matching with corresponding letters on letter profiles for lowering side levers and consequently for disengaging the letter profiles from their retaining plates to open the lock. This invention is designed to prevent opening of a lock without the designated card. 
     Today women who used to take care of homes are employed outside the home, and hence often nobody is at home during office hours. This then has become a good time for thefts. Such a burglary or theft not only causes loss of property but psychological injury to the victims can occur also. Such theft is mainly caused by the lack of reliable locks, and the fact that conventional locks can usually be opened by common tools. Therefore, home security is a primary concern. The lack of basic theft-proof facilities has become a public problem. 
     In view of the above problem, the Inventor has created a card-operated lock to provide a reliable lock which can not be opened by any tool other than the designated card. 
     SUMMARY OF THE INVENTION 
     The main objective of the present invention is to provide a card-operated lock using a card with embossed letters which match corresponding letters on letter profiles in the lock for lowering levers therein and consequently disengaging the letter profiles from their retaining plates to open the lock. The lock of this invention can not be opened without the designated card. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a card-operated lock according to the present invention. 
     FIG. 2 is a perspective view of the card-operated lock and card assembled according to the present invention. 
     FIGS. 3 (A)-(E) are sequential side sectional views illustrating operation of the card-operated lock according to the present invention as the card is inserted. 
     FIGS. 4 (A) and (B) are top sectional views illustrating operation of the card-operated lock according to the present invention wherein insertion of the card frees the lock shackle. 
     FIGS. 5 (A) and (B) are perspective views of another embodiment of card-operated lock according to the present invention. 
     FIGS. 6 (A) and (B) illustrate sequential operation of the card-operated lock embodiment of FIGS. 5 (A) and (B) according to the present invention. 
     FIGS. 7 (A)-(C) illustrate further sequential operation of the embodiment of card-operated lock of FIGS. 5 (A) and (B) according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The card-operate lock (10) according to the present invention includes a sliding block (21) with a sliding plate (22), and a set of letter profiles (25) which are matched precisely so that no tool other than a particularly designed card can open the lock. Lock (10) also has upper and lower housing members (11) and (12) and a shackle (50). 
     FIG. 3 illustrates the relationship between card (61) and lock (10) according to the present invention. When the card (61) is inserted into a card inserting slot (15) at the back of the lock (10), its front end abuts sliding plate (22), which in turn abuts point R on upper lock portion (11). Card (61) gets contacts three internal blocks (29) beneath the sliding plate (22) so that a plurality of, for example, three embossed letters (62) on the card (61) can contact their corresponding letter profiles (25) evenly. When the embossed letters (62) on the card (61) match the engraved letters (251) on the letter profiles (25), the card (61) can be pressed downwardly slightly so that the sliding plate (22) is displaced downwardly by the front edge of the card (61) retained by the point R at the sliding plate (22). Consequently, when the engraved letters (251) are filled by the embossed letters (62), depressing card (61) causes the letter profiles (25) to depress side levers (26) at both sides of the letter profiles (25) into their corresponding chambers (31) in retaining plates (30), respectively, and sliding plate (22) is lowered until its front edge is lower than a stop element (13) at on upper housing (11). The sliding block (21) can then be moved farther. 
     As shown in FIG. 4, when the sliding block (21) is moved forward, its front fork (211) pushes slant surface (42) on each of two sliding pieces (41) so that its longitudinal thrust is converted to traverse thrust by its movement on the slant surface (42). Hence, the two sliding pieces (41) which retain a shackle (50) at two side retaining notches (51) are retracted and disengaged from the retaining notches (51). The shackle (50) is then forced to move by compression spring (52), and the lock is opened. 
     FIG. 5 shows an alternative embodiment for the letter profiles (25) and the retaining plates (30). Due to changes in the shapes of the card (61), the letter profiles (25) and the retaining plates (30), use of the sliding plate (22) with its supporting posts (23) and springs (24) can be eliminated. As shown in FIGS. 6 and 7, after the card (61) with hollow letters (62) is inserted into the card inserting slot (15), the letter profiles (25) are depressed for a depth equal to the height of a upper stepped portion (252) of such embossed letters (251) on the letter profiles (25). Each side lever (26) then reaches the position Y in the chamber (31). Then, if the card (61) is pushed forward further, the embossed letters (251) on the letter profiles (25) will pop up into their corresponding hollow letters (62) on the card (61) until the uppers stepped portions (252) reach the card (61). The side levers (26) are located at the position X of the chambers (31). Consequently, the sliding block (21) can be pushed forward to open the lock. This design then which can prevent opening of; the lock by any tool other than the designated card.

Summary:
A card-operated lock using a card with embossed letters matching with corresponding letters on letter profiles in the lock for lowering of side levers on the letter profiles and consequently disengaging the letter profiles from their retaining plates to open the lock. The lock is designed to prevent opening thereof without the designated card.