CARTRIDGE DOOR-LATCHING MECHANISM

Abstract: Door-latching mechanism for a molded plastic cartridge (10, 30, 50) includes a plastic arm (14, 34, 54) 5 projecting from a wall of the cartridge (10, 30, 50) and acting as a cantilevered spring. At the free end of the arm are a door-locking pawl (19, 39, 59) which locks the door when the spring (10, 30, 50) is at rest and unlocks the door when the spring (10, 30, 50) is flexed. When the 10 cartridge (10, 30, 50) is a VHS or Betamax videocassette, upon inserting it into a recorder, a finger of the recorder depresses the arm (14, 34, 54) and with it the door-locking pawl (19, 39, 59), thus unlocking the pawl (19, 39, 59) and allowing the door to be opened. The arm (14) may either be 15 integral with the cartridge (10, 30, 50) or molded as a separate plastic piece (36, 56) to be attached to the cartridge (10, 30, 50).

Description: The invention concerns a cartridge such as, for example, a videocassette of the VHS or Betamax format having a door and a door-latching mechanism. The visor-like door of a VHS or Betamax videocassette is spring-loaded to open when a latch is depressed upon contacting a finger of the recorder. Originally, the latching mechanism for each of those videocassettes had two pieces, typically a molded plastic latch plate and a metal spring. The recently issued US Patent No. 4,475,700 (MacLeod et al) discloses such a 2-piece door-latching mechanism for a VHS videocassette which is said to be easier to assemble and less expensive than prior 2-piece mechanism. Some VHS videocassettes that have recently appeared on the market employ a latching mechanism consisting of a single piece of molded plastic such as shown in US Patent No. 4,466,583 (Giannis et al). Although such a latching mechanism simplifies assembly and should be significantly less expensive, its plastic spring member, the "elongate resilient arm 60" of Figs 1-5, is under compression when the door is closed as can be seen by comparing Figs 7 and 8. Because any plastic member will experience plastic flow or creep if kept under compression, the arms 60 and 68 should gradually lose their effectiveness as spring members, especially in warm weather. We are not aware of any simplification of the 2-piece latching mechanism of the Betamax videocassette, the latch of which is formed with an inclined plane which upon being contacted by the aforementioned finger of the recorder, is depressed to unlock the door. EP-A-142,897 discloses a cartridge comprising a moulded plastic casing on which is pivotably mounted a door affording access to the interior of the cartridge, said casing having an opening in a wall thereof and a door-latching mechanism comprising a plastic arm projecting from the wall to provide a cantilevered plastic spring, the free end of the arm being formed with a door-locking pawl which looks the door when the spring is in its rest position and unlocks the door when the spring is flexed. The present invention provides a cartridge as disclosed in EP-A-142,897 characterised in that said casing comprises a base and cover assembly, said arm extends through said opening and is a separate plastic member attached to the casing by a tongue which fits into a groove which groove is formed in a sidewall of said base and extends from an open edge of said sidewall whereby said tongue is secured in place by said cover assembled to said base. Preferred features of the invention are defined in the dependent claims. The cartridge door-latching mechanism utilised in the cartridge of the present invention is assembled easily and, although entirely molded plastic, has substantially no plastic-flow problems. Furthermore, we believe it to be far more cost effective than any door-latching mechanism heretofore proposed for the VHS or Betamax videocassettes. When the cartridge is a VHS or Betamax videocassette, for example, the opening may be formed in a sidewall of the base of the casing. When the cartridge is a VHS videocassette, the free end of the arm may for example be formed with two outward-projecting knobs, one in position to serve as said door-locking pawl and the other an unlocking knob in position to be depressed to unlock the pawl. Upon inserting the videocassette into a VHS recorder, a finger of the recorder depresses the unlocking knob and with it the door-locking pawl, the unlocking the pawl and allowing the door to be opened. When the cartridge is a Betamax videocassette, the free end of the arm may for example be formed with an outward-projecting knob in position to serve as said door-locking pawl, and my for example also be formed with an inclined plane which functions in the sane manner as do the inclined planes of latches of previous Betamax videocassettes. In VHS and Betamax designs, the arm of the novel door-latching mechanism remains in the flexed position while the videocassette is in place in the recorder, but because any given videocassette is rarely in a recorder for more than a small fraction of its life, this should not result in a damaging degree of plastic flow. Immediately upon removing the videocassette, the arm is released end returns to its unflexed, at-rest position with the door-locking pawl in place to lock the door. In a VHS or Betamax videocassette, the groove will preferably extend from the open edge of the sidewall about 3/4 of the sidewall height. The tongue slides into the groove from said open edge and can then be secured by assembling the cover to the base. Plastics currently favored for molding the casings of videocassettes are polystyrene and acrylonitrile-butadiene-styrene (ABS) resins, the former being more widely used because it is of lower cost, is easy to mold with good accuracy, and has adequate resistance to impact. The cantilevered spring of the novel door-latching mechanism has higher flexural modulus and better resistance to both fatigue and plastic flow when the arm is molded from acetal resin. Because acetal resin tends to warp and does not lend itself to incorporation of welded windows, it may be used to mold the arm as a separate piece while the casing is molded from polystyrene or ABS resin. Preferred embodiments of the invention are described below by way of example only with reference to Figures 1 to 4 of the accompanying drawings wherein: Fig 1 is a fragmentary elevation of VHS videocassette in accordance with the invention; Fig 2 is a cross section along line 5-5 of Fig 1; Fig 3 is a fragmentary top view of a Betamax videocassette in accordance with the invention; and Fig 4 is a fragmentary elevation of the videocassette of Fig 3. The VHS videocassette fragmentally illustrated in Figs 1 and 2 has a molded plastic base 30 and cover (not shown) that together provide a casing on which is pivotably mounted a visorlike door (shown in phantom). A separately molded plastic piece 36 is formed with an arm 34, at one end of which is a tongue 37 that is triangular in cross section. The base 30 is formed with a groove 41, also triangular in cross-section, into which the tongue 37 slidably fits, after which the tongue is secured in place by assembling the cover to the base. At the free end of the arm 34 is an unlocking knob 40 and an extension 43 from which outwardly projects a door-locking pawl 39 which also has a knob shape. The pawl 39 and knob 40 extend through an opening 32 in the base 30 and function as follows. Upon inserting the videocassette into a recorder (not shown), a finger of the recorder depresses the unlocking knob, thus pivotably flexing the arm 34 and carrying with it the door-locking pawl 39. Retraction of the pawl releases the door to be opened by forces exerted in loading the videocassette into the recorder. Upon removing the videocassette from the recorder, the spring action of the arm 34 returns it with its pawl and unlocking knob to the unflexed position. The Betamax videocassette fragmentally shown in Figs 3 and 4 has a molded plastic base 50 and cover 51 that together provide a casing on which is pivotably mounted a visor-like door (shown in phantom). A separate plastic piece 56 has a triangular tongue 57 that fits into a groove 60 in the base 50 and is secured by assembling the cover onto the base. At the other end of the plastic piece 56 is an arm 54, and free end of which is formed with a door-locking pawl 59 that projects through an opening 52 in the wall of the base 50. Upon inserting the videocassette into a recorder (not shown), a finger of the recorder contacts an inclined plane 61 which also is formed in the arm. This pivotably flexes the arm, thus unlocking the door-locking pawl 59 to release the visor-like door. Upon removing the videocassette from the recorder, the arm 54 returns to the position illustrated in Fig 3 and causes the door which is spring-loaded to close and to be locked by the pawl 59.

Claims: A cartridge comprising a moulded plastic casing on which is pivotably mounted a door affording access to the interior of the cartridge, said casing having an opening in a wall thereof and a door-latching mechanism comprising a plastic arm projecting from the wall to provide a cantilevered plastic spring, the free end of the arm being formed with a door-locking pawl which locks the door when the spring is in its rest position and unlocks the door when the spring is flexed, characterised in that said casing comprises a base (30, 50) and cover (51) assembly, said arm extends through said opening and is a separate plastic member (36, 56) attached to the casing by a tongue (37, 57) which fits into a groove (41, 60) which groove is formed in a sidewall of said base (30, 50) and extends from an open edge of said sidewall whereby said tongue (37, 57) is secured in place by said cover (51) assembled to said base. A cartridge as claimed in claim 1 wherein said arm (34) carries at its free end an unlocking knob (40) which projects through said opening and can be depressed to unlock said pawl (39). A cartridge as claimed in clam 1 or claim 2 wherein said door-locking pawl (39) is formed with a chamber to cause it to be depressed when struck by a closing door. A cartridge as claimed in any preceding claim wherein said pawl (59) projects through and is closely spaced from the adjacent edge of said opening so that when the pawl engages the door, any force tending to accidentally open the door pushes the pawl against said adjacent edge. A cartridge as claimed in any preceding claim wherein said plastic arm (34, 54) is composed of acetal resin. A cartridge as claimed in any preceding claim which is a videocassette cartridge.

Inventors: CYBULSKI, CLAUDE E. C/O MINNESOTA MINING AND, JOHNSON, GREGORY H. C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1987
Main classification: G11B23
IPC codes: G11B23