AU614390B2 - A novel screw drive mechanism - Google Patents

Description

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COMMONWEALTH OF AUSTRALIA Patents Act 1952 COMPLETE SPECIFICATION

(ORIGINAL)

Application Number Lodged Complete Specification Lodged Accepted Published Priority Related Art Class Int. Class S*4 o a 0 0 6 a 0 0 0 9 adt Name of Applicant Address of Applicant Actual Inventor CHAOLAI FAN 112 Stalin Street, Changchun, Jilin Province, Peoples Republic of China CHAOLAI FAN Address for Service Complete Specification for the Invention entitled: The following statement is a invention including the best me:- H. R. HODGKINSON CO.

Patent Trade Mark Attorneys 26A Alfred Street MILSONS POINT NSW 2061 "A Novel Screw Drive Mechanism" full description of this method of performing it known to -1- 1OAVO C L~, a! THE PRESENT INVENTION relates to a novel screw drive mechanism which permits the screw to engage quickly with or disengage quickly from a stationary screw nut by means of a vertical lifting of the screw. This mechanism can be widely used in a manual bench vice, a bench vice for a tool or a sliding table of a tool where there are requirements for quickly passing over an idle stroke, speedily adjusting a relative distance or fast clamping.

There are many known types of quick clamping vices. U.S.

Pat. No. 2102602 (1937) discloses a mechanism in which the locus of centre in the screw is an arc when the screw disengages or engages with the nut. Thus, the nut has to slidably connect with a stationary body, which would render it with poor strength. U.S. Pat. No. 2430458 (1947) also S discloses a mechanism in which the screw nut will still remain on the screw after the latter has disengaged from the 0 00ooo former and where the screw nut bears against an outer 0 circumference of the screw by a spring and a pin, thereby S0o resulting in too great a resistance. U.S. Pat. No. 2672776 &o oo (1954) discloses a mechanism, the operation of which a 0 requires simultaneously employing two handles and is inconvenient for working.

There are also many known types of fast splitting screw drive mechanism, the one being in common use is a type of split screw nut. However, it is used only in a narrow o, domain since the drive mechanism is very complex in construction. Moreover, the present applicant submitted a patent application to the European Patent Office (No.

S 88301613 see FIG. which disclosed a fast clamping S 0 mechanism, in which a driving nut is provided outside the vice body, and the mechanism is complex in construction.

40000 0 0 0000 eODo o 0000 000000 o 0 00 00 0 000 00 00 00 0 0 0 @00000 o 0 oo~ 0O0000 0 0 0 0 0 OO00 0 00 0 0 oo oo 0 0 0 o An object of the present invention is to overcome the aforesaid drawbacks by employing a one-direction ratchet type cam mechanism to provide for the screw moving vertically so that the screw engages with or disengages from the screw nut quickly. This mechanism is simple in construction and is low in cost.

According to the present invention there is provided a vertical-lift screw drive mechanism comprising a stationary body, a movable body, a screw, a screw nut seat in the form of a saddle, the nut seat having a hole therethrough and having cam support surfaces thereon, an eccentric cam positioned between two arms of said nut seat, said cam having a hole therethrough, said screw disposed in the holes of said nut seat and said cam, said cam slidably supported on the cam support surfaces of said nut seat, a one-direction ratchet device positioned between said screw nut seat and said eccentric cam, said ratchet device connected to said screw such that said screw causes said eccentric cam to rotate by means of said one-direction ratchet device, thereby causing a vertical movement of said screw whereby said screw engages with or disengages from the nut seat.

The mechanism according to one aspect of the present invention comprises a movable sliding body, a stationary body, a screw, a screw nut seat, a cam, a ratchet sleeve, a spring and a guide key, wherein the screw passes through the cam and the ratchet sleeve while the two ends of the screw are supported in two long-circular holes in two end walls of the movable sliding body respectively. The ratchet sleeve is mounted between the eccentric cam and an arm of the screw nut seat and connects with the screw by means of the guide p.ALL 3 Qu-i

C.-

key. There is provided one or more one-direction clutch pawls on the end face of the sleeve and each pawl has a vertical surface and an oblique surface which may engage correspondingly with a vertical surface and an oblique surface in one or more pawl grooves of the eccentric cam.

The sleeve is beared against one end surface of the cam by a spring.

In the case of clamping a workpiece, turning a handle clockwise (in a right hand direction) drives the screw and the ratchet sleeve in simultaneous rotation resulting in the oblique surface of the pawl bearing against the oblique surface of the pawl groove of the cam so as to rotate the cam. Meanwhile, the screw is lifted under the action of an upward stroke curve of the cam so that the outer threads of the screw will engage with the inner threads of the screw 0 0008 nut seat. Continuing to rotate the handle, a positioning 00ooo plane of the cam will be reached, which stops the rotation 6000 S of the cam, while the screw may continue to rotate :o clockwise. Thus the pawl of the ratchet sleeve produces an 0o 0 000 axial component force as a result of the action of the 00 00 0 0 oblique surface of the cam pawl groove and the pawl will slide out from the groove when the axial component is greater than the axial pressure of the spring. Since the S screw engages with threads of the screw nut seat, the screw 0 o will be forwardly displaced when it rotates, and will push the movable sliding body forward so as to achieve the goal 6t of quickly clamping a workpiece.

Similarly, in the case of releasing a workpiece, turning the handle counterclockwise (left hand direction) results in rotation of the screw and ratchet sleeve, causing the pawl of the sleeve to fall into the cam pawl groove. The vertical surface of the pawl touches the vertical surface of the cam pawl groove and causes the cam to rotate to the left, thus allowing the screw to descend under the action of the downward stroke curve of the cam, so that the threads of the screw and screw nut seat disengage. Then the movable body may be pulled or pushed freely to achieve the goal of quickly adjusting (in about one second) the opening of the jaws of the vice.

The present invention will be explained by reference to the accompanying drawings as follows, taking a bench vice as an embodiment.

FIG. 1 is a view showing a screw drive mechanism of the prior art.

FIG. 2 is a sectional view showing a bench vice employing the drive mechanism according to the invention, in 4o°° a released position.

a640 o FIG. 3 is a sectional view of the bench vice of FIG. 2, 400eo0 a 0 o but in a position clamping a workpiece.

ao FIG. 4 is a general view of the screw nut seat of FIG. 2.

00 S0 FIG. 5 is a side view of FIG. 4.

FIG. 6 is a perspective view of the ratchet sleeve of FIG. 2.

FIG. 7 is a perspective view -f the eccentric cam of (#4006 S' FIG. 2.

%ate S9 FIG. 8 is a sectional view of FIG. 2 taken from line AA 1 and DD, showing a relative position of the screw 044t neck journal in the support holes of the front and back vertical plate of the movable body, when the bench vice is in a released position.

00 0 FIG. 9 is a sectional view of FIG. 2 taken from line BB, showing a relative position after the outer threads of the screw have been disengaged from the inner threads of an axial hole in the screw nut seat, when the bench vice is in a released position.

FIG. 10 is an orthogonal projection drawing of the local view E showing the pawl of the ratchet sleeve engaging with the pawl groove on the cam when the bench vice of FIG. 2 is in a released position.

FIG. 11 is a sectional view taken from line CC of FIG. 2, showing the relative position of the eccentric cam and the screw nut seat when the bench vice is in a released position.

FIG, 12 is a sectional view taken from line A'A' and line D'D' of FIG. 3 showing a relative position of the screw neck journal in the support holes on the front and back vertical plate of the movable body, case 4964 4when the bench vice is in a position clamping a workpiece.

FIG. 13 is a sectional view taken from line B'B' of FIG.3, showing a position where the outer threads of the screw engage with the inner threads of the screw nut seat when the bench vice is in a clamping position.

S FIG. 14 is an orthogonal projection drawing of the local ag&view E' showing the pawl of the ratchet sleeve o00 having been disengaged from the pawl groove of the cam in FIG. 3 when the bench vce is in a clamping position.

FIG. 15 is a sectional view of FIG. 3 taken from line &GasC'C', showing a relative position of the eccentric cam and the screw nut seat when the bench vice is in a clamping position.

FIG. 16 is a view of a second embodiment of the present w rm4W invention, showing a bench vice for a tool in a released position.

FIG. 17 shows the bench vice of FIG. 16 in a clamping position.

FIG. 18 is a perspective view of the pawl pin of FIG.16.

FIG. 19 is a perspective view of the eccentric cam of FIG. 16.

FIG. 20 is a perspective view of the ring extension spring of FIG.16.

FIG. 21 is a perspective view of the screw nut seat of FIG. 16.

FIG. 22 is a sectional view taken from line DD of FIG. 16.

FIG. 23 is a sectional view taken from line EE of FIG. 16.

FIG. .24 is a sectional view taken from line FF of FIG. 16.

FIG. 25 is a sectional view taken from line D'D' of FIG. 17.

FIG. 26 is a sectional view taken from line E'E' of FIG. 17.

FIG. 27 is a sectional view taken from line F'F' of o <FIG. 17.

o o 9 FIG. 28 is a view of a third embodiment of the present o invention, showing a bench vice in a released :0 °o position.

FIG. 28 shows the bench vice of FIG. 28 in a clamping position.

FIG. 30 is a perspective view of the screw nut seat of FIG. 28.

FIG. 31 is a sectional view taken from line PP of FIG. 28.

FIG. 32 is a sectional view taken from line P'P' of ;y i FIG. 29.

FIG. 2 shows an embodiment of the bench vice employing the drive mechanism with a vertical lift screw according to the 7 ~p X~-ma(ii r-=*lu~F* present invention, which comprises a stationary body or table 21; a movable body 22; a pair of vice jaws 12, 14; a handle 1, a screw 20, an eccentric cam 17, a screw nut seat 19, a ratchet sleeve 9, a compression spring 8 and a gasket 6, wherein the movable body 22 can slide along the guide track in the stationary table 21 and the handle 1 mounted through a hole on the left end of the screw 20 causes the screw to turn to the left or the right.

Two ends of the screw 20 are supported respectively in the support holes 7,23 on the front and back vertical plates of the movable body 22. The two support holes 7,23 being in a long-circular form permit the screw 20 only to move up and down vertically. The gasket 6 is provided between an inner end surface 68 on a left projection of the screw 20 and an outer end surface of the support hole 7 on the front vertical plate of movable body 22. At the right shoulder of the screw 20, there is provided a cylindrical compression spring 44, one end of which by means of a gasket 41 bears against the inner side of the back vertical plate of movable 46- body 22, while the end of the right neck journal of screw .00o9: g has a gasket 42 and a stop collar 43 to prevent the neck 9, 0db journal from sliding off.

In assembly, it should be ensured that there is a gap6 between the surface 60 on the left projection of the screw and the end surface 61 of the gasket 6. The width of 0S, should be about 1/2 of the pitch in screw 20. This gap is provided to avoid the teeth accidentally touching against the threads 25 and 15 so that they bind, by allowing the O t screw 20 to have a little free axial movement so that a suitable engagement can be achieved.

9 q The screw 20 is provided with a key groove which connects with the ratchet sleeve 9 by mean of the guide key 16. The screw 20 also penetrates the axial hole of the ratchet sleeve 9. In addition, the screw 20 has outer threads (see FIG. 2 and 3).

The screw nut seat 19 is in the form of a saddle (see FIG.

which is fixed on the stationary body 21 by means of the bolts 11. The two arms 40 on the seat 19 have respectively concentric holes 38. The cross-sectional shape of the holes 38 is formed with two circular arcs, i.e. the upper arc "a" and the lower arc (see FIG. The centre of the circle of the upper arc is 01 and the central angle o of the arc is no more than 1800. The radius of the upper arc is r, which is equal to the thread radius of the outer threads 25 on screw 20. The surfaces on the upper arcs of the two holes each have respectively inner threads 15 which can engage with the outer threads 25 of the screw 20. The centre of the circle oooo of the lower arc is 02 which is beneath the centre 01 of 800 the upper arc There is an eccentric distance "e" 0 between the two centres 01 and 02. The value of should 00 oo0o be greater than the tooth depth of the threads 15,25.

I'l 00 so or 0 0 Meantime the radius r 2 of the lower arc should be greater than the thread radius of the outer threads 25 on screw 20 in order to ensure that when the screw 20 descends from position 01 to position 02, it does not touch with any 400 V portions of the wall of the hole of seat 19 as shown in FIG.

9 and can be displaced freely along the axial direction of 0o screw The eccentric cam 17 is positioned between an arm 40 and the so 09

S

~PL1 49 Qc~0 sleeve 9. The curve for the cam is divided into a downward stroke curve portion (with the lowest point 32) and an upward stroke curve portion (with the highest point 31). In addition the cam 17 has also a positioning projection 52 and a positioning plane 51. In anti-clockwise rotation (left turning), the positioning projection 52 will touch a horizontal limit plane 56 of the movable body 22. At this point, the lowest point 32 on the cam curve will just oppose the supporting surface 24 of seat 19 resulting in the cam 17 and the screw 20 being situated in the most released position 02 (see FIG. 11).

Similarly (see FIG. 15) in clockwise rotation (right turning), the positioning plane 51 will touch the side wall surface 55 on the movable body 22. At this point, the highest point 31 on th= upward stroke curve portion of the cam 17 will touch the cam support surface 24. Under the influence of the upward stroke curve of cam 17, the axis of screw 20 will be caused to ascend from position 02 up to 4644 position 01, so that the outer threads 25 engage with the 9 00 inner threads 15 on the seat 19 (see FIG. 13).

S Oda 069o°0 There is provided on an end surface 45 of cam 17 one or more 6 a 0 one-direction pawl grooves 53 (see FIG 14), which have a vertical surface 50 and an oblique surface 49.

The ratchet sleeve 9 connects with screw 20 by means of the 4 guide key 16 and has a flange 57 which is provided with one or more one-direction pawls 58. The latter has a vertical €surface 47 and an oblique surface 48 (see FIG. 10), so that o8€ under the action of the cylindrical compression spring 8, it is ensured that the ratchet sleeve 9 and the cam 19 are pressed together.

ly -rn rn rn Now, the operation sequences for a fast clamping bench vice according to the invention will be explained as follows.

There are five steps wherein the second and third steps are simultaneous and the whole operating time thereof is about one second; the fourth and fifth steps are also simultaneous and the whole operating time is about 0.5 second.

The step for free adjustment of the opening in the jaws of a bench vice.

At the lowest point 32 on the downward stroke curve of the cam 17, when it opposes the cam supporting surface 24, the cam 17 is in a released position relative to the cam supporting surface 24 of the screw nut seat 19 (see FIG. 11). The front end and the back end of the screw 20 are supported respectively on the lower o oooo supporting surfaces 36 and 37 of the supporting holes 7 0 0 ooo and 23 on the front and back vertical plates of the 0o o 000 movable body 22 (see FIG. Meantime, the positions aooe of the supporting holes 7 and 23 ensure that the 00 00 Soo central axis of the screw 20 is at the centre 02 of the 00 00 o 0 lower arc while the outer threads 25 on screw do not contact with the inner surfaces on the holes 38 of the seat 19 over any portion (see FIG. Thus the movable body 22 may be pushed or pulled manually, so that the movable body 22 can slide quickly along the 0 00 guide track in the stationary body 21 together with the 20, thereby quickly adjusting the opening S of 0 the vice jaws according to the size of the workpiece Depending on the size of the workpiece 28, the process for pushing the movable body into a suitable position ~,00 0 0 0 0o o so as to cause the jaws 12, 14 to contact with the workpiece 28 will take about 0.5-1 second.

The step for engaging the outer threads of screw with the inner threads of seat.

Turning handle 1 clockwise (right-hand direction as shown by the arrow M in FIG. 3) rotates the screw The screw 20 by means of the guide key 16 also causes the ratchet sleeve 9 to turn to the right. Meanwhile, the pawl 58 of ratchet sleeve 9 is in the pawl groove 53 of cam 17. Clockwise rotation of the ratchet sleeve 9 causes the oblique surface 48 of pawl 58 to bear against the oblique surface 49 of pawl groove 53 (see the position designated by the double dash line in FIG.

14). Thus, by means of the axial force from the compression spring 8, the engagement of the oblique su -face 48 on ratchet sleeve 9 causes the cam 17 also to turn to the right, thus causing its upward stroke 0 curve to slide on the cam supporting surface 24 of the 040 0000 screw nut seat 19 until the position plane 51 of the 000000 0 a cam 17 contacts with the limit surface 55 to stop the 00" cam. from further rotation (see FIG. 15). At the same 00 0111 time, the highest point 31 on the upward stroke curve of the cam 17 just touches the supporting surface 24 of the seat 19. The screw 20 also lifts vertically to its highest position, i.e.'the central axis of screw ascends over an eccentric distance e" from its original position 02-02 to a position 0 _01, until the outer threads 25 of screw 20 engage with the threads 00 in the holes 38 of seat 19. The engagement should be provided with some gap to allow the pair of the inner and outer threads 15, 25 to turn freely relative to 00 00each other (see FIG. 13).

The step for clamping a workpiece (see FIG. 3).

Continuing to turn the handle 1 clockwise (as shown by the arrow M) causes the rotative moment of the ratchet sleeve 9 to be applied to the oblique surfaces 48 and 49 belonging to the pawl 50 and pawl groove 53, since the positioning plane 51 of the cam 17 has now touched the sidewall limit surface 55 of the movable body 22 thus causing the cam 17 to cease rotation (see FIG.

Having thus been contacted with each other, there is generated an axial component along the direction When the axial component is greater than the axial pressure of spring 8, the ratchet sleeve 9 is displaced along the direction until the pawl 58 leaves pawl groove 53 and slides along the end surface of cam 17. Still continuing to turn the handle causes the screw 20 to move forward along the axial OO direction while it turns to the right, since the G00* o0 outer threads 25 of screw 20 have engaged with inner Oooo0 threads 15 of seat 19, the threads being righthanded a 0 :0 and the seat 19 fixed on the stationary body 21. Thus, 0 the screw 20 by means of the end surface 60 on its left 00 00 00 0 0 projection and gasket 6, causes the movable body 22 to be displaced until the jaws 12, 14 clamp the workpiece 28.

o° The step for releasing a workpiece.

After the workpiece has been processed and it is required to be removed, turning the handle 1 in an anticlockwise direction (N-direction, see FIG. 2) 0 causes the screw 20 to rotate anticlockwise. Since the So o 0 outer threads 25 of screw 20 are initially in 13 Mu.

'D

~1 engagement with the inner threads 15 of seat 19, the screw 20 is displaced axially along the direction "H" while turning to the left, and by means of the gasket 42 and stop collar 43 it causes the movable body 22 to be displaced along direction thereby causing the jaws to release the workpiece 28.

The step for disengaging the outer threads of the screw from the inner threads of the seat (see FIG. 2).

At the time of releasing the workpiece, i.e. the time when the handle 1 turns to the left, the ratchet sleeve 9, driven by the screw 20 and guide key 16, also turns to the left through a certain angle until the pawl 58 falls into the pawl groove 53 (see FIG. 10) under the pressure of the compression spring 8. Since the pawl is of a one-direction clutch type, the screw 20 causes the ratchet sleeve 9 to continue turning counterclockwise, thus causing the cam 17 to turn in a

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lefthand direction by means of the two vertical surfaces 47 and 50 respectively on the pawl 58 and pawl o9 o.groove 53, thereby causing the lowest point 32 on the a 0 downward stroke to turn gradually to its lowest position (see FIG. 11), until the positioning projection 52 of cam 17 contacts the horizontal limit plane 56. Thus a downward component force W is applied t it41 to screw 20, forcing the central axis of the screw to descend from position 01 to position 02, just itl dropping a height Hence the outer threads 25 of screw 20 are wholly disengaged from the inner threads of seat 19. Now, the front end and the back end of 4 bIt screw 20 fall respectively onto the lower supporting surfaces 36, 37 of the supporting holes 7,23 on the 11~ IUIII front and back vertical plates of the movable body 22 (see FIG. Therefore, the screw 20 may be freely displaced forwardly or backwardly together with the movable body 22, thus causing the screw driving mechanism to be again left in a manner such that the opening of the vice jaws 12, 14 can be quickly adjusted as described in step 1.

FIGS. 16-27 show a second embodiment according to the present invention, which is a bench vice for a tool and comprises a stationary body 63, a movable body 64, a screw an eccentric cam 65, a screw nut seat 68, a onedirection pawl pin 73, a ring extension spring 76, and a positioning pin 74.

In this embodiment, the one-direction ratchet device is in the form of a pawl pin 73 instead of the ratchet sleeve 9 in the first embodiment. The movable body 64 can slide along the guide track in the stationary body 63 and the screw 0 passes through the holes in the eccentric cam 65 and the screw nut seat 68. The screw nut seat 68 is in the form of 8 0 o. a saddle with an upper top portion 88 (see FIG. 21), and is Sooo0 fixed on the stationary body 63 by means of the bolts SThe holes of the screw nut seat 68 are in the form of longcircular holes, which have two parallel side walls 87, a upper arc portion 86, and a, lower arc portion with the inner threads 15 suitable to engage with the outer threads 25 of the screw 20. The width of the long-circular holes is S substantially equal to the diameter of the screw 1 The eccentric cam 65 is located within the screw nut seat 68 and the curve portion 92 of eccentric cam 65 is circular and can slide between the upper cam support surface 94 and the o lower cam support surface 95 of nut seat 68. The eccentric cam 65 is provided on the plane 89 with a radial hole 67 and a threaded hole 90. The eccentric cam 65 is further provided with a groove 77 for receiving a ring extension spring 76, said groove 77 surrounding the outer circumference of cam 65 and passing through the end centre of radial hole 67 (see FIG.19).

The positioning pin 74 is secured in the threaded hole 90 of cam 65 by threads. The pawl pin 73 is located within the radial hole 67 of the cam 65 and can slide radially along the hole 67. The pawl pin 73 is provided with a one-way pawl formed by a vertical surface 79 and an oblique surface 78. The pawl pin 73 is further provided with a hole through which the ring extension spring 76 can pass. The ring extension spring 76 is located around the groove 77 of the cam 65 and passes through the hole 80 of the pawl pirn rrao o 73. The screw 20 is provided along its axial direction with 0a C two one-direction pawl grooves 81 formed by a vertical surface 83 and an oblique surface 82 (see FIGS. 24 and 27).

00 Oo' The front end plate of movable body 64 is provided with two holes in which the springs 71 are located, the springs 71 can ensure that there is a gap "6 between the front end wall and the gasket 70, thereby providing the screw 20 with a little axial movement so that a suitable engagement can be achieved. A gasket 93 is located on the inner side of the Sfront end wall of the movable body and prevents the screw from sliding off.

In the case of releasing a workpiece (see FIG. 16), turning ~the srrew 20 counterclockwise (N-direction) causes the pawl pin 73 to fall into the pawl groove 81 of screw 20 under the pin 73 to fall into the pawl groove 81 of screw 20 under the

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action of the ring extension spring 76. Thus the screw drives the eccentric cam 65 by means of the two contacted vertical surfaces 83 and 79 respectively on the pawl groove 81 and the pawl 73 (see FIG. 24). Thus the eccentric cam rotates under the influence of the two cam support surfaces 94 and 95 and causes the screw 20 to ascend vertically along the two parallel side walls 87 of the holes of the nut seat 68, until the head of the positioning pin 74 contacts with the limit surface 84 of the nut seat 68 (see FIG. 23), with the axis of screw 20 ascending from its lowest position 02-02 to its highest position 01-01, thereby causing the threads 25 of screw 20 to disengage from the threads 15 of nut seat 68 (see FIG. 22). Thus the movable body 64 may be pushed or pulled manually such that the opening of the vice jaws can be quickly adjusted (see FIG. 16).

S In the case of clamping a workpiece, turning the screw S clockwise (M-direction) causes the oblique surface 82 of the ,o pawl groove 81 of screw 20 to bear against the oblique f" surface 78 of pawl pin 73 (see FIG. 27), thus causing the or' r eccentric cam 65 to rotate under the pulling action of the ring extension spring 76, until the head of the positioning pin 74 contacts with the upper limit surface 85 of the nut seat 68 (see FIG. 26). In'the meantime, the rotation of the eccentric cam 65 causes the screw 20 to descend along the two parallel walls 87 of the long circular holes of nut seat S" 68, with the axis of the screw 20 dropping from its highest 0 position 01-01 to its lowest position 02-02, thereby causing the threads 25 of screw 20 to engage with the threads 15 of nut seat 68 (see FIG. Continuing to turn the screw 20, causes the oblique surface 82 of pawl pin 73 to slide along the oblique surface 82 of ~I I- pawl groove 81 of screw 20, whilst the component force acting on the two oblique surfaces is greater than the extension force of the ring spring 76, until the pawl pin 73 drops out of the pawl groove 81 (see FIG. 27). Then the screw 20 can continue to turn. Since the outer threads of screw 20 have engaged with the inner threads 15 of nut seat 68, with the seat 68 fixed on the stationary body 63, the screw 20 will move forward along the axial direction "K" whilst turning to the right. This causes the movable body 64, by means of the gasket 70, to clamp the workpiece.

FIGS. 28-32 show a third embodiment according to the present invention wherein the structures of the pawl pin, the eccentric cam and the nut seat are basically identical to those of the second embodiment, but the nut seat 68 is provided on its bottom surface with a guide pillar 96 which can slide vertically along a guide hole 97 on the base 100 of the stationary body 63. The screw is supported on two holes of two end walls of the movable body 64 and can not move vertically up and down but can only turn, while the nut a a a seat 60 can move vertically under the action of the eccentric cam 65, so that the threads 25, 15 of screw 20 and nut seat 68 may engage with or disengage from each other.

af o a In the case of clamping a workpiece, turning the screw clockwise (M-direction), causes rotation of the eccentric cam 65 by means of the pawl groove and pawl pin 73. Thus the eccentric cam 65 rotates under the influence of the two surfaces 94 and 95, and causes the nut seat 68 to ascend vertically over a distance because the screw 20 is fixed in the radial direction, (see FIG. 29 and FIG. 32).

Thus the threads 15 of nut seat 68 engage with the threads of screw 20. Continuing to turn the screw 20 until the r o 'a 0' P"Llq 18 AS O~A r~ e i pawl pin 73 slides out of the pawl groove of the screw causes the screw 20 to move along the axial direction "K" while it continues to turn to right, thereby causing the movable body 64, by means of the gasket 70, to clamp the workpiece (see FIG. 29).

In the case of releasing a workpiece, turning the screw counterclockwise (N-direction), causes the screw 20 to drive the eccentric cam 65 by means of the contacted vertical surfaces 83 and 79 respectively on the pawl groove 81 and the pawl pin 73. Thus the cam 65 rotates causing the nut seat 68 to descend vertically relative to the radially fixed screw 20, so that the threads 25 of screw 20 disengage from the threads 15 of nut seat 68 and the movable body can be freely moved in the axial direction (see FIG. 28).

The mechanism may have a variety of modifications in structure which should be considered within the scope of the S present invention.

0 6 9 0 9 99 4444 1 9 IL 49 4/ I 99

Claims (6)

1. A vertical-lift screw drive mechanism comprising a stationary body, a movable body, a screw, a screw nut seat in the form of a saddle, the nut seat having a hole therethrough and having cam support surfaces thereon, an eccentric cam positioned between two arms of said nut seat, said cam having a hole therethrough, said screw disposed in the holes of said nut seat and said cam, said cam slidably supported on the cam support surfaces of said nut seat, a one-direction ratchet device positioned between said screw nut seat and said eccentric cam, said ratchet device connected to said screw such that said screw causes said eccentric cam to rotate by means of said one-direction ratchet device, thereby causing a vertical movement of said screw whereby said screw engages with or disengages from the nut seat.

2. The screw drive mechanism according to claim 1 wherein 4 1 0 0 a 0 said one-direction ratchet device is a ratchet sleeve, *06* 4*06 0 positioned between an arm of said screw nut seat and an end surface of said eccentric cam, a guide key being provided for connecting the screw to the ratchet sleeve 0 000 and further comprising a one-direction pawl provided on 00 00 0 an end surface of the ratchet sleeve, a one-direction pawl groove correspondingly provided on the end surface of the eccentric cam, the pawl being formed by a vertical surface and an oblique surface, a spring being 0 provided for biasing the ratchet sleeve and the end 0. a surface of the cam together along an axial direction.

3. The screw drive mechanism according to either claim 1 P, L lxi or claim 2 wherein said screw has a threaded outer surface and said screw nut seat has matching inner threads on the hole thereof such that during upward displacement of the screw, the threaded outer surface engages the inner threads of the nut seat to clamp a workpiece, and during a downward displacement, the threaded outer surface disengages from the inner :hreads of the nut seat.

4. The screw drive mechanism according to claim 3 wherein said eccentric cam has a one-direction pawl groove formed by a vertical surface and an oblique surface and has a positioning projection for touching a horizontal limit plane of the stationary body, providing the lowest point on a downward stroke of the cam such that the screw attains its lowest position thereby disengaging the inner and outer threads; and further comprising a position plane on the cam for touching with a vertical limit side surface of the movable body, providing the highest point on an upward stroke of the cam to contact with the cam support surface on the screw nut seat to cause the screw to ascend to its highest position, such that the outer threads of the 4 screw engage with the inner threads of the seat in a rotatable manner. The screw drive mechanism according to any one of the preceding claims wherein the screw nut seat is fixed on the stationary body, the two arms of the nut seat having concentric axial holes, each hole having an upper circular arc and a lower circular arc, the central angle of the upper circular arc being no more than 1800 and the radius of the upper circular arc 21 being equal to the radius of the outer threads on the screw, a fitting surface of the upper circular arc having inner threads suitable to engage with the outer threads on the screw, a centre of the lower circular arc positioned beneath a centre of the upper circular arc, the radius of the lower circular arc being greater than the radius of the outer threads on the screw and the eccentric distance between the centres of the two circular arcs being greater than the tooth depth of the screw threads.

6. The screw drive mechanism according to any one of the preceding claims wherein a spring, a gasket and a stop collar forming an assembly are disposed between a right end neck journal of the scr i and a back vertical plate of the movable body, a gap being provided between the end surface on a left projection of the screw and an end surface of the gasket on a side surface of the movable body. 4 4 44*4 4

44.4 7. The screw drive mechanism according to any one of the *81444 preceding claims wherein two neck journals, each on a 14 left end and right end of said screw, are respectively It *4 So4 supported in two holes of l.ong-circular shape on front and back end plates of said movable body, each of said two holes having two vertical parallel side walls, the width of the holes being substantially equal to the diameter of said screw, said screw being able to move 4 4 up and down along a vertical direction. 44 8. The screw drive mechanism according to claim 1i, wherein the said one-direction ratchet device is in the form of a radial pawl pin positioned within a radial hole of 22 <U said eccentric cam, the pawl pin being formed with a vertical surface and an oblique surface; a ring extension spring being positioned within a groove on the outer circumference of said eccentric cam and passing through a hole on said pawl pin. 9. The screw drive mechanism according to claim 8 wherein the said screw is provided along its axial direction with pawl grooves formed with a vertical surface and an oblique surface. The screw drive mechanism according to either claim 8 or claim 9 wherein the said nut seat further has an upper cam support surface and a pair of holes therethrough, the holes of said nut seat being of long-circular shape, each having two vertical parallel wails; the width of said long-circular holes being substantially equal to the diameter of said screw, a lower arc portion of said long-circular holes having 4 threads suitable to engage with threads provided on *4I. said screw. ;r 11. The screw drive mechanism according to any one of claims 8 to 10, wherein a curve portion of said eccentric cam is circular, said cam being provided with a radial hole for receiving said pawl pin and with a groove for receiving said ring extension spring around its circumference, a positioning pin being fixed on said eccentric cam; said eccentric cam being so S:l4 arranged that when it causes said screw to ascend from its lowest position to its highest position, the threads of said screw disengage from the threads of said nut seat; and when said cam causes said screw to 4 i 23 descend from its highest position to its lowest position, the threads of the screw engage with the threads of said nut seat. 12. The screw drive mechanism according to claim 1 wherein the stationary body comprises a base portion and said nut seat is provided on its bottom surface with a guide pillar suitable to slide vertically along a guide hole on the base portion of said stationery body. 13. The screw drive mechanism according to claim 13 wherein said screw is fixed in its radial direction, said eccentric cam causing said nut seat to move vertically relative to said radially fixed screw, so that the threads of said nut seat can engage with or disengage from the threads of said screw. 14. A bench vice employing the screw drive mechanism according to any one of the preceding claims wherein the bench vice has a stationary jaw and a movable jaw, the screw drive mechanism being disposed in the bench vice, the stationary body being the stationary jaw and I the movable body being the movable jaw. t 4 4 4 A screw drive mechanism substantially as disclosed herein in conjunction with FIG. 2 to 15, FIG. 16 to 27 4 or FIG. 28 to 32. Dated this 31st day of May 1991 CHAOLAI FAN BY: ,P t <A :Patent Attorneys for the Applicant