Magnetic tape cassette

Abstract: A tape cassette comprises a case body consisting of an upper half case and a lower half case (3), a pair of hubs contained in the case body and holding a magnetic tape thereon, and a locking member placed in a recess formed in the inner surface of the bottom wall of the lower half case so as to be brought into engagement with the respective circumferences of the hubs to lock the hubs and disengaged from the respective circumferences of the hubs to unlock the hubs. The locking member has a tail portion having a surface consisting of convex, curved working surfaces, and the unlocking pin of a recording/reproducing apparatus engages either of the convex, curved working surfaces to shift the locking member to the unlocking position when the tape cassette is inserted in the recording/reproducing apparatus. Rails are formed on the bottom surface of the recess to support the locking member for smooth sliding movement thereon and the ribs include two ribs (3j3,3j4) formed at a position corresponding to the tail portion of the locking member and inclined in opposite directions at an angle to the direction of sliding movement of the locking member, substantially conforming to the shape of the tail portion.

Description: The present invention relates to a tape cassette provided with a locking member for locking the hubs contained therein while the tape cassette is not in use. Some practical tape cassettes holding a tape for the high-density recording of video signals or PCM signals, such as 1/2 in. video tape cassettes and 8 mm video tape cassettes, are provided with a locking member for locking hubs contained therein while the tape cassettes are not in use and kept for storage. Such a locking member is pressed by the resilience of a spring against the hubs to lock the hubs when the tape cassette is not in use. The locking member is separated from the hubs by an unlocking pin to unlock the hubs when the tape cassette is inserted in a tape drive. Such tape cassettes provided with a locking member are disclosed, for example, in EP-A-411,622, EP-A-431,914, EP-A-323199, GB-A-2145999, US-A-4742415 and US-A-4650136. The locking member can be guided between walls extending in the sliding direction and which may converge. Similar arrangements are disclosed in US-A-5,210,670, US-A-5,267,114, and US-A-5,276,580. Figs. 1a and 1b of the accompanying drawings are a schematic plan view and a schematic side view, respectively, of a prior art tape cassette in an inoperative state, and Figs. 2a and 2b are a schematic plan view and a schematic side view, respectively, of the same prior art tape cassette in an operating state, in which indicated at 61 is a locking member, at 62 are hubs, at 63 indicated by alternate long and short dash lines is the case body 63 of the tape cassette and at T is a tape held on the hubs 62. The locking member 61 is provided with locking protrusions 61a which engage teeth 62a formed in the circumferences of the hubs 62 to lock the hubs 62 and has the shape of a substantially T-shaped flat plate. A locking spring 61c, such as a stainless steel spring wire, has opposite ends connected to knuckles 61b 1 and 61b 2 , and a middle portion engaging a peg 64 formed on the inner surface of the case body 63. Normally, namely, when the tape cassette is not in use, the locking member is biased toward the hubs 62 by the locking spring 61c so that the locking protrusions 61a engage the teeth 62a to lock the hubs 62 as best shown in Fig. 1a. When the tape cassette is inserted in a recording/reproducing apparatus, an unlocking pin 65 enters the tape cassette through an opening 63a formed in the case body 63 and engages the edge 61d of the locking member 61 provided with flat slopes 61d 1 and 61d 2 at a position corresponding to the opening 63a to push the locking member 61 up against the resilience of the locking spring 61c as shown in Fig. 2b, so that the locking protrusions 61a are disengaged from the teeth 62a to unlock the hubs 62 as shown in Fig. 2a. The locking member 61 is provided with a slot 61f and a guide pin 66 formed on the inner surface of the case body 63 is fitted in the slot 61f to guide the locking member 61 for sliding movement between a locking position shown in Fig. la and an unlocking position shown in Fig. 2a. When pushed by the unlocking pin 65, the locking member 61 slides in a space between the hubs 62 along the inner surface of one of the halves of the case body 63. Since the locking member 61 has the shape of a flat plate and in close contact with the inner surface of the half of the case body 63, it occurs, in some cases, that the locking member 61 is unable to slide smoothly. As disclosed in EP-A-450976, on which the precharachterising portion of claim 1 is based, it is possible to avoid plane contact between the locking member 61 and the inner surface of the half case of the case body 63 to ensure the smooth sliding movement of the locking member 61 by forming ribs parallel to the direction of movement of the locking member 61 on the inner surface of the half of the case body 63 and making the locking member 61 slide along the ribs. However, the locking member 61 is liable to be supported on the ribs within the case body 63 of the tape cassette in an unstable position and unable to lock the hubs 62 properly. In such a prior art hub locking arrangement, the unlocking pin 65 slides along the flat slope 61d 1 (61d 2 ) to push the locking member 61 against the resilience of the locking spring 61c and a considerably large force is exerted on the point of contact between the flat slope 61d 1 (61d 2 ) and the extremity of the unlocking pin 65, which hinders the entrance of the unlocking pin into the tape cassette and abrades the flat slope 61d 1 (61d 2 ). Accordingly, it an object of the present invention to provide a tape cassette provided with a locking member for locking hubs contained therein, capable of being smoothly moved between a locking position and an unlocking positon. The present invention provides a tape cassette comprising: a case body consisting of mating half cases; a pair of hubs contained within the case body and holding a tape-like recording medium thereon; and a locking member placed in a recess formed in the inner surface of the bottom wall of one of the mating half cases so as to be brought into engagement with the respective circumferences of the hubs to lock the hubs and disengaged from the respective circumferences of the hubs to unlock the hubs; a plurality of ribs formed on the bottom surface of the recess formed in the inner surface of the bottom wall of the half case, a lower face of the locking member being supported for sliding movement on top of the plurality of ribs, characterised in that the plurality of ribs comprise ribs inclined to the direction of sliding movement of the locking member. The ribs extending at an angle to the direction of sliding movement of the locking member in conformity with the shape of the sliding surface of the locking member and formed on the inner surface of the half case enable the locking member to slide smoothly on the ribs in line-contact with the ribs and to stabilizes the position of the locking member. The locking member may have a tail portion having a surface consisting or convex, curved working surfaces of varying curvature, and the unlocking pin of a recording/reproducing apparatus engages either of the convex, curved working surfaces to move the locking member toward an unlocking position when the tape cassette is inserted in the recording/reproducing apparatus. Since the unlocking pin engages the convex, curved working surface of varying curvature of the locking member, the locking member can be moved toward the unlocking position by a relatively small force exerted on the convex, curved working surface by the unlocking pin. The present invention will be further described by way of illustrative example in the following description taken in connection with the accompanying drawings, in which: Figs. 1a and 1b are a schematic plan view and a schematic side view, respectively, of a prior art tape cassette, in which a locking member is at a locking position; Figs. 2a and 2b are a schematic plan view and a schematic side view of the tape cassette of Figs. 1a and 1b, in which the locking member is at an unlocking position; Fig. 3 is a plan view of a lower half case of a tape cassette in a preferred embodiment according to the present invention; Fig. 4 is a perspective view of the tape cassette in the preferred embodiment according to the present invention; Fig. 5 is a perspective view of the perspective view of assistance in explaining the relation between the tape cassette of Fig. 4 and a magnetic head drum; Fig. 6 is a plan view of the tape cassette of Fig. 4, in which-a second half case is removed; Fig. 7 is a plan view of assistance in explaining the positional relation between the tape cassette of Fig. 4 and the magnetic head drum of Fig. 5; Figs. 8a, 8b, 8c, 8d and 8e are a top plan view, a sectional view taken on line A-A in Fig. 8a, a rear view, a side view and another side view, respectively, of a locking member included in the tape cassette of Fig. 4; Figs. 9a and 9b are fragmentary sectional views of the tape cassette of Fig. 4; Fig. 10 is an enlarged, sectional view of the tail portion of the locking member of Figs. 8a to 8e, having a surface consisting of convex, curved working surfaces; Fig. 11 is a fragmentary sectional view of assistance in explaining the positional relation between the locking member of Figs. 8a to 8e, and an unlocking pin; and Fig. 12 is a graph of assistance in explaining the unlocking function of the unlocking pin. A tape cassette in a preferred embodiment according to the present invention will be described hereinafter with reference to Figs. 3 to 9. The tape cassette in this embodiment is a subminiature tape cassette of about 20 mm in width and about 30 mm in length. Referring to Figs. 3 to 9, a tape cassette 1 holding a magnetic tape for recording, for example, PCM signals thereon and for reproducing, for example, PCM signals recorded thereon has a case body formed by fastening together an upper half case 2 and a lower half case 3 with screws 4, and provided with a lid 6 covering a front opening 5 formed in the front side of the case body. As shown in Figs. 4, 5 and 6, a pair of hubs 7 and 8 are contained in the case body of the tape cassette 1 at positions corresponding to openings 2a and 2b formed in the upper half case 2 and openings 3a and 3b formed in the lower half case 3, respectively, and a magnetic tape T is held on the hubs 7 and 8 so as to pass from one of the hubs 7 and 8 to the other and vice versa. A portion of the magnetic T extending between pinch rollers 9 and 10, which serve also as guide rollers, supported for rotation at the opposite ends of the front opening 5 is accessible from outside. Erase inhibit mechanisms 12 and 13 are formed across the upper half case 2 and the lower half case 3 in the upper and lower walls of the case body of the tape cassette 1 at positions near the opposite corners on the side of the rear wall of the case body, respectively. Positioning holes 15, 16 and 17 are formed in the case body at the middle and near the opposite corners, respectively, on the side of the rear wall of the case body. A plurality of holes 18 and 19 for detection are formed in the case body along the rear wall of the case body. Gripping recesses 20 and 21 are formed in the side walls of the case body at positions near the rear end of the case body. As best shown in Figs. 4 and 5, the lid 6 for covering the front opening 5 of the case body is provided with a rack 23 formed in a lateral groove 22 formed in its front wall. When the tape cassette 1 is inserted in a cassette magazine, a cassette changer engages the rack 23 in ejecting the tape cassette 1 from the cassette magazine. Windows 2c and 3c of a transparent resin are formed in the central portion of the top wall of the upper half case 2 and the central portion of the bottom wall of the lower half case 3, respectively, to enable the recognition of the quantity of the magnetic tape T on the hubs 2 and 3. When the tape cassette 1 is loaded on a recording/reproducing apparatus, the recording/reproducing apparatus records signals on the magnetic tape T and reproduces signals recorded on the magnetic tape T by a helical scanning method with a rotary head. Referring to Fig. 5, a rotary head 41 revolves along a circle inclined at a predetermined angle to a head cylinder 42. A portion of the head cylinder 42 is received in the tape cassette 1 through the front opening 5 opened by turning up or down the lid 6 of the tape cassette 1. The rotary head 41 records signals on inclined tracks extending obliquely across the magnetic tape T while the magnetic tape T slides along the surface of the portion of the head cylinder 42 received in the tape cassette 1. As shown in Fig. 6, in which the upper half case 2 is removed, a pair of tape guide members 24 and 25 having guide surfaces 24a and 25a inclined in opposite directions, respectively, are disposed on the inner sides of the pinch rollers 9 and 10, respectively, to guide the magnetic tape T so as to slide helically along the circumference of the head cylinder 42. Accordingly, the respective guide surfaces 24a and 25a of the tape guide members 24 and 25 extend close to and along the circumference of the head cylinder 42 to guide the magnetic tape T along the circumference of the head cylinder 42. The rotary magnetic head is provided with wing guides 43 and 44 respectively having rollers 43a and 44a at their front ends. The wing guides 43 and 44 are disposed on the opposite sides of the head cylinder 42. When the tape cassette 1 is inserted in the recording/reproducing apparatus, the wing guides 43 and 44 are disposed between the pinch roller 9 and the tape guide member 24 and between the pinch roller 10 and the tape guide member 25, respectively, to press the magnetic tape T against the tape guide members 24 and 25. The wing guides 43 and 44 are disposed between a support member 26 and a tape guide 28 formed between the support member 26 and the pinch roller 9, and between a support member 27 and a tape guide 29 formed between the support member 27 and the pinch roller 10, respectively. Referring to Fig. 6 showing the internal arrangement of the tape cassette 1, the hubs 7 and 8 consist of inner hubs 7a and 8a in which hub driving shafts are inserted and outer hubs 7b and 8b put on the inner hubs 7a and 8a so as to be axially movable relative to the inner hubs 7a and 8a and restrained from turning relative to the inner hubs 7a and 8a, respectively. Locking teeth 7a 1 and 8a 1 are formed in the respective circumferences of at least portions of the inner hubs 7a and 8b projecting from the outer hubs 7b and 8b toward the lower half case 3, respectively. A locking member 11 is placed in a recess 3e formed in the inner surface of the lower half case 3. The locking member 11 engages the teeth 7a 1 and 8a 1 of the hubs 7 and 8 to lock the hubs 7 and 8 when the tape cassette 1 is not in use. Referring to Figs. 8a to 8e, the locking member 11 has locking protrusions 11a 1 and 11a 2 to be brought into engagement with the teeth 7a 1 and 8a 1 of the hubs 7 and 8, knuckles 11b 1 and 11b 2 , a locking spring 11c, such as a stainless steel spring wire, held on the knuckles 11b 1 and 11b 2 , a tail portion 11d having convex, curved working surfaces 11d 1 and 11d 2 , a slot 11f and a substantially triangular opening 11g. The locking member 11 is formed of an engineering plastic, such as POM. Normally, i.e., when not in use, the locking member 11 is biased toward a locking position by the locking spring 11c strained by a pressing nose 3d formed within the cassette 1 as shown in Fig. 6 and the locking protrusions 11a 1 and 11a 2 are in engagement with the teeth 7a 1 and 8a 1 of the inner hubs 7a and 8a, respectively, as shown in Fig. 9(a) to lock the hubs 7 and 8. The locking member 11 is formed by insert molding, in which the locking spring 11c is fastened firmly to the knuckle 11b 1 at its one end so that the locking spring 11c may not come off the locking plate 11. The locking spring 11c is held loose at the other end between the two lugs 11b 2a and 11b 2b of the knuckle 11b 2 . The combination of the locking member 11 and the locking spring 11c by insert molding eliminates a process of assembling the locking member 11 and the locking spring 11c, facilitates the tape cassette assembling work and reduces the cost of the tape cassette 1. When the tape cassette 1 is inserted in the recording/reproducing apparatus, a positioning pin 99 provided in the recording/reproducing apparatus enters the tape cassette 1 through the positioning hole 15 of the upper half case 2 or the lower half case 3 as shown in Figs 9b to position the tape cassette 1 correctly in the recording/reproducing apparatus. The positioning pin 99 serves also as an unlocking pin. The positioning pin 99 comes into contact with the convex curved working surface 11d 1 (11d 2 ) of the tail portion 11d to shift the locking member 11 toward the front side of the tape cassette 1. The movement of the tape cassette 1 is guided by guide pins 3f and 3g inserted respectively in the slot 11f and the opening 11g of the locking member 11 and, consequently, the locking protrusions 11a 1 and 11a 2 of the locking member 11 are disengaged from the teeth 7a 1 and 8a 1 as shown in Fig. 9b to enable the hubs 7 and 8 to rotate. Since the guide pin 3g is inserted in the substantially triangular opening 11g and does not determines the lateral position of the locking member 11, the locking member 11 is able to turn on the guide pin 3f. When the tape cassette 1 is ejected from the recording/reproducing apparatus, the positioning pin 99 comes out of the positioning hole 15, the locking member 1 is shifted from the unlocking position (Fig. 9b) to the locking position (Fig. 9a) by the resilience of the locking spring 11c to lock the hubs 7 and 8. As shown in Figs. 9a and 9b, the inner hub 8b (7b) is provided with teeth 8a 1 (7a 1 ) also in the circumference of a portion projecting from the outer hub 8b (7b) toward the upper half case 2. Thus, the hubs 7 and 8 can be disposed in the case body indifferently to their orientation when assembling the tape cassette 1, which facilitates work for assembling the tape cassette 1. Although the locking member 11 underlies the window 3c of the lower half case 3, the quantity of the magnetic tape held on the hubs 7 and 8 can be recognized through the window 3c and the locking member 11 because the locking member 11 is formed of a transparent resin by molding. The locking member 11 may be provided with an opening that enables the observation of the magnetic tape T held on the hubs 7 and 8 therethrough regardless of the position of the locking member 11. Transparent friction sheets, not shown, are interposed between the inner surface of the upper half case 2 and the upper ends of the hubs 7 and 8 and between the inner surface of the lower half case 3 and the lower ends of the hubs 7 and 8 to secure the smooth rotation of the hubs 7 and 8, to prevent the entanglement of the magnetic tape T and to prevent the lost motion of the hubs 7 and 8. Thus, the hubs 7 and 8 are restrained from unnecessary rotation by the locking member 11 when the tape cassette is not in use. As shown in Figs. 3 and 6, ribs 3j (3j 1 to 3j 4 .) of a height on the order of 0.03 mm are formed on the bottom surface of the recess 3e receiving the locking member 11 therein and the locking member 11 is supported in line contact on the ribs 3j 1 to 3j 4 for sliding movement. Thus, the locking member 11 is able to slide smoothly on the ribs 3j 1 to 3j 4 . The ribs 3j 1 and 3j 2 nearer to the front side of the case body are extended in parallel to the direction of sliding movement of the locking member 11. The ribs 3j 3 and 3j 4 nearer to the rear side of the case body are inclined in opposite directions, respectively, at an angle to the direction of sliding movement of the locking member 11, substantially conforming to the shape of the sliding surface of the locking member 11. Thus, the locking member 11 is securely supported in a horizontal position on the ribs 3j 1 to 3j 4 for reliable locking. Although the locking member 11 is able to turn in a horizontal plane, the ribs 3j 3 and 3j 4 will not interfere with the edges of the tail portion 11d of the locking member 11 to obstruct the locking operation of the locking member 11, because the ribs 3j 3 and 3j 4 converge toward the positioning hole 15. The number, length and direction of extension of the ribs 3j are not limited to those specifically described herein and may be changed according to the shape of the locking member 11. The present invention is not limited in its application to the subminiature tape cassette described herein; the present invention is applicable also to various tape cassettes provided with a locking member for locking the hubs. Fig. 10 is an enlarged, fragmentary sectional view of the tail portion 11d of the locking member 11 having a surface consisting of convex, curved working surfaces 11d 1 and 11d 2 of varying curvature. In Fig. 10, indicated by alternate long and two short dashes lines is the contour of the working surfaces of the tail portion of a locking member employed in a prior art tape cassette. When shifting the locking member 11 from the locking position shown in Fig. 9a to the unlocking position shown in Fig. 9b, the positioning pin 99 engages the convex, curved working surface 11d 2 (11d 1 ) of the locking member 11. As the positioning pin 99 is inserted gradually in the tape cassette 1 as indicated by continuous lines, alternate long and short dash lines and broken lines as shown in Fig. 11. Fig. 12 shows the variation of the unlocking force, namely, the thrust acting on the positioning pin with the depth of insertion of the positioning pin 99 in the tape cassette 1. In Fig. 12, continuous lines indicate the unlocking force for the tape cassette 1 of the present invention, and alternate long and two short dashes lines indicate the unlocking force for the prior art tape cassette provided with the locking member provided with flat slopes. In calculating the unlocking force, it was assumed that the initial strain of the locking spring 11c is 0.4 mm, the diameter of the locking spring 11c is 0.16 mm, and friction between the relevant parts is negligible. As is obvious from Fig. 12, the convex, curved working surface 11d 2 (11d 1 ) reduces effectively the maximum load (the load on the positioning pin 99 when the positioning pin is at a distance of about 2 mm from the final position) exerted on the positioning pin 99 by the locking spring 11c. Accordingly, the abrasion of the convex, curved working surfaces 11d 1 and 11d 2 by the positioning pin 99 is reduced and the positioning pin 99 is able to be inserted smoothly in the tape cassette 1. The curvatures of portions of the convex, curved working surfaces are determined properly taking into consideration the design conditions for the relevant parts including the locking spring and the positioning pin so that the load on the positioning pin 99 is reduced to the least possible extent.

Claims: A tape cassette (1) comprising: a case body consisting of mating half cases (2,3); a pair of hubs (7,8) contained within the case body and holding a tape-like recording medium (T) thereon; and a locking member (11) placed in a recess (3e) formed in the inner surface of the bottom wall of one of the mating half cases (2,3) so as to be brought into engagement with the respective circumferences of the hubs (7,8) to lock the hubs (7,8) and disengaged from the respective circumferences of the hubs (7,8) to unlock the hubs (7,8); a plurality of ribs (3j) formed on the bottom surface of the recess (3e) formed in the inner surface of the bottom wall of the half case, a lower face of the locking member (11) being supported for sliding movement on top of the plurality of ribs (3j), characterised in that the plurality of ribs (3j) comprise ribs (3j 3 , 3j 4 ) inclined to the direction of sliding movement of the locking member (11). A tape cassette according to claim 1, wherein the plurality of ribs (3j) further include ribs (3j 1 , 3j 2 ) extending parallel to the direction of sliding movement of the locking member (11). A tape cassette according to claim 1 or 2, wherein there are at least a pair of ribs (3j). A tape cassette according to claim 1, 2 or 3 wherein said locking member (11) has a tail portion (11d) having a surface consisting of convex, curved working surfaces (11d 1 , 11d 2 ) which are positioned to engage an unlocking pin of a recording/reproducing apparatus to shift the locking member (11) to the unlocking position when the tape cassette is inserted in a recording/reproducing apparatus.

Inventors: TAGUCHI OSAMU, TAGUCHI, OSAMU, Taguchi, Osamu, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: G11B23
IPC codes: G11B15, G11B23