EP0354644B1

EP0354644B1 - Screw drive mechanism and vice

Info

Publication number: EP0354644B1
Application number: EP89305364A
Authority: EP
Inventors: Chaolai Fan
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-08-08
Filing date: 1989-05-26
Publication date: 1994-07-27
Anticipated expiration: 2009-05-26
Also published as: RU2052692C1; JPH0288179A; RU2052691C1; MY104146A; GB8917443D0; EP0354644A3; DE8907067U1; DE68917047T2; DE68917047D1; AU3710189A; AU614390B2; MX172487B; EP0354644A2; JPH0543464B2; BR8903962A; NZ229177A; GB2221634A

Description

This invention relates to a screw drive mechanism which permits a screw to engage with or disengage from a screw nut quickly by a relative movement between the screw and the nut, and may be applied in a manual bench vice, bench vice for a tool, or the sliding table of a tool where there is a requirement for quickly passing through an idle stroke, speedily adjusting a relative distance or fast clamping.
There are many known types of fast clamping vice. US-A-2102602 (1937) disclosed a vice mechanism having the features of the preamble of present claim 1, but in which the locus of centre of the screw is an arc when the screw disengages or engages to the nut. Thus, the nut has to connect slidingly with a stationary body, which would give poor strength. US-A-2430458 (1947) also discloses a mechanism in which the nut will remain on the screw after they are disengaged, and where the nut is pressed against an outer circumference of the screw by a spring and a pin. This will cause a large resistance. My own EP-A-306119 (which is in Article 54(3) EPC relation to this patent) disclosed a fast clamping mechanism, in which a driving nut is provided outside the vice body. The mechanism is complex in construction.
According to the present invention, a screw driven mechanism (having the features of the preamble of claim 1) is characterised in that
the nut seat has axially-spaced arms with respective axially aligned slotted holes through which the screw passes, the slot elongation being in the direction of said transverse relative movement of the screw and nut seat;
the eccentric member is an eccentric cam positioned around the screw between the arms of the nut seat and which has an outward cam surface which slidably engages a cam support surface of the nut seat, and
the relative transverse movement which engages/disengages the thread is guided in one plane either by the nut seat or by correspondingly slotted holes in the first body, through which holes the screw extends.
The straight relative movement between the screw and nut threads, when engaging/disengaging, reduces the above-mentioned difficulties of the prior art while enabling a construction that may be relatively simple and hence not too expensive to make.
According to one embodiment of the present invention, the nut seat is a saddle fixed to the second body and the engagement/disengagement movement is guided in one plane by axially aligned slotted holes having parallel side walls spaced substantially by the diameter of the screw, to guide the screw, and the pawl connection comprises a sleeve fitting around the screw next to the eccentric cam between the arms of the nut seat, and constrained by a key to rotate with the screw, the sleeve being urged axially against the eccentric cam by a spring, and a pawl on the sleeve being engageable in a ratchet recess of the eccentric cam. Under the action of the cam, the screw can be vertically moved relative to the secured nut seat.
In a second embodiment of the present invention, the pawl connection is by a pawl pin comprised in the eccentric cam member and spring-urged radially inwardly against the screw, which has a ratchet recess for engagement by the pawl pin so that the screw and cam member can rotate together, and the relative transverse movement which engages/disengages the thread is guided in one plane by the nut seat.
In a third embodiment of the present invention, the nut seat is connected to the second body by a guide pillar which slides in a guide hole in the second body. The screw is transversely fixed relative to the first body and the engagement/disengagement movement is guided in one plane by the guided transverse movement of the nut seat relative to the second body. The screw is thus secured in the radial direction, while under the action of the cam the nut seat itself can move vertically relative to the radially secured screw.
Embodiments of the invention are now described by way of example, referring to the accompanying drawings in which:

Fig. 1 is a view showing a bench vice mechanism of the prior art;
Fig. 2 illustrates a bench vice employing a drive mechanism embodying the invention, in a sectional view showing the bench vice in a released position;
Fig. 3 is a sectional view of the bench vice of Fig. 2 in a position clamping a workpiece;
Fig. 4 is a general view of a screw nut seat of the vice of Fig. 2;
Fig. 5 is a side view of Fig. 4;
Fig. 6 is a perspective view of a ratchet sleeve of the vice of Fig. 2;
Fig. 7 is a perspective view of an eccentric cam of the vice of Fig. 2;
Fig. 8 is a sectional view of Fig. 2 taken at lines AA and DD;
Fig. 9 is a sectional view of Fig. 2 at line BB, showing a relative position after the screw has been disengaged from an axial hole in the screw nut seat, with the vice in a released position;
Fig. 10 is an orthogonal projection drawing of the local view E, showing how the pawl of the ratchet sleeve engages with a groove on the cam when the vice of Fig. 2 is in a released position;
Fig. 11 is a sectional view taken at line CC of Fig. 2, showing relative positions of the eccentric cam and the screw nut seat when the vice is in a released position;
Fig. 12 is a sectional view taken at line A'A' and line D'D' of Fig. 3, showing relative positions of the screw neck journal in the support holes of the front and back vertical plates of the movable body, when the bench vice is in a position clamping a workpiece;
Fig. 13 is a sectional view taken at line B'B' of Fig. 3, showing how 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;
Fig. 14 is an orthogonal projection of the local view E', showing how the ratchet sleeve disengages from the groove of the cam (of Fig. 3) with the bench vice in a clamping position;
Fig. 15 is a sectional view of Fig. 3 taken at line C'C', showing relative positions 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 bench vice embodying the invention, in a released position;
Fig. 17 shows the bench vice of Fig. 16 in a clamping position;
Fig. 18 is a perspective view of a pawl pin of the Fig. 16 vice;
Fig. 19 is a perspective view of an eccentric cam of the Fig. 16 vice;
Fig. 20 is a perspective view of a ring extension spring of the Fig. 16 vice;
Fig. 21 is a perspective view of a screw nut seat of the Fig. 16 vice;
Fig. 22 is a sectional view at line DD of Fig. 16;
Fig. 23 is a sectional view at line EE of Fig. 16;
Fig. 24 is a sectional view at line FF of Fig. 16;
Fig. 25 is a sectional view at line D'D' of Fig. 17;
Fig. 26 is a sectional view at line E'E' of Fig. 17;
Fig. 27 is a sectional view at line F'F' of Fig. 17;
Fig. 28 is a view of a third bench vice embodying the invention, in a released position;
Fig. 29 shows the bench vice of Fig. 28 in a clamping position;
Fig. 30 is a perspective view of a screw nut seat of the Fig. 28 vice;
Fig. 31 is a sectional view at line PP of Fig. 28; and
Fig. 32 is a sectional view at line P'P' of Fig. 29.

Figs. 2-15 show a bench vice which comprises a stationary body 21 having a hollow portion; a movable body 22 positioned within the hollow portion; a pair of vice jaws 12,14; a handle 1, a screw 20, an eccentric cam 17, a screw nut seat 19, ratchet sleeve 9, a compression spring 8 and a gasket 6. The movable body 22 can slide along the guide track in the stationary body 21 and the handle 1, mounted in a through-hole at the left-hand end of the screw 20, may cause the screw to turn to the left (N-direction) or right (M-direction).
The two ends of the screw 20 are supported in respective support holes 7,23 of the front and back vertical plates of the movable body 22. The two support holes 7,23 are both in an oval form having two parallel side walls 101, the width of the holes being substantially equal to the diameter of the screw so as to permit the screw 20 to move up and down only vertically. The gasket 6 is provided between an inner end surface 68 of a left projection of the screw 20, and an outer end surface of the support hole 7 of the front vertical plate of the movable body 22. At the right shoulder of the screw 20, there is a cylindrical compression spring 44 whose end bears through a gasket 41 against the inner side of the back vertical plate of the movable body 22, while the end of the right neck journal of screw 20 has a gasket 42 and a stop collar 43 to prevent the neck journal from sliding off. In assembly, it should be ensured that there is a gap δ between the end surface 60 on left projection of the screw 20 and the end surface 61 of gasket 6. The width of δ is about ½ of the pitch in screw 20. This δ is needed in case the threads meet out of alignment when moved together; a little axial freedom of movement enables a suitable engagement to be achieved.
The screw 20 has a key-way which connects with the ratchet sleeve 9 through a guide key 16. The screw 20 also passes through the axial hole of the ratchet sleeve 9. The screw 20 has outer threads 25 (see Figs. 2 and 3).
The screw nut seat 19 is in the form of a saddle (see Fig. 4), which is fixed on the stationary body 21 by means of bolts 11. The two arms 40 of the seat 19 have respective concentric holes 38. The cross-sectional shape of the holes 38 features two circular arcs, the upper arc "a" and the lower arc "b" (see Fig. 5). The centre of circle of the upper arc "a" is 0₁ and the central angle of the arc "a" is no more than 180°. The radius of upper arc "a" is r₁ and equals the thread radius of the outer threads 25 on screw 20. The surfaces of the upper arcs "a" of the two holes have respective inner threads 15 which can engage with the outer threads 25 of the screw 20. The centre circle of the lower arc "b" is 0₂, beneath the centre 0₁ of the upper arc "a", and there is an eccentricity distance "e" between the two centres 0₁ and 0₂. The distance "e" should be greater than the tooth depth of the threads 15,25, and the radius r₂ of the lower arc "b" should be greater that the thread radius of the outer threads of the screw 20 so that when the screw 20 descends from position 0₁ to position 0₂, it need not touch any portions of the wall of the hole (as shown in Fig. 9) and hence can displace freely along its axial direction.
The eccentric cam 17 is positioned between one arm 40 and the ratchet sleeve 9. The curve of 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) (see Fig. 7). The cam 17 has also a positioning projection 52 and a positioning plane 51. In leftwards turning, the positioning projection 52 will meet 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 so that the cam 17 and the screw 20 are in the most released position 0₂ (see Fig. 11). Similarly (see Fig. 15) in rightwards turning, the positioning plane 51 will meet the side wall surface 55 of the movable body 22. At this point, the highest point 31 on the upward stroke curve portion of the cam 17 will meet the cam support surface 24, under the influence of the upward stroke curve of the cam 17, causing the axis of the screw 20 to ascend from position 0₂ up to position 0₁, so that its outer threads 25 engage with the inner threads 15 on the seat 19 (see Fig. 13). There is provided on an end surface 45 of cam 17 one (or more) one-way pawl groove 53 (see Fig. 7 and Fig. 14) which has a vertical surface 50 and an oblique surface 49.
The ratchet sleeve 9 connects with the screw 20 through the guide key 16 and has a flange 57 which is provided with a (one or more) pawl 58 formed by a vertical surface 47 and an oblique surface 48 (see Fig. 6 and Fig. 10). A cylindrical compression spring 8 ensures that the ratchet sleeve 9 and the cam 19 are always pressed together.
Now, the operation sequences of the vice will be explained. There are five steps, wherein the second and third steps are simultaneous and the whole operating time is about one second; the fourth and fifth steps are also simultaneous and the whole operating time is about 0.5 second.

(1) Free adjustment of the jaw opening of a bench vice is described first.

When the lowest point 32 on the downward stroke curve of the cam 17 faces 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 supporting surfaces 36 and 37 of the supporting holes 7 and 23 of the movable body 22 (see Fig. 8). The positions of the supporting holes 7 and 23 keep the central axis of the screw 20 at the centre 0₂ of the lower arc "b", while the outer threads 25 do not contact at all with the inner surfaces of the holes 38 of the seat 19 (see Fig. 9). Thus the movable body 22 may be pushed or pulled manually such that the movable body 22 slides quickly along the guide track in the stationary body 21 with the screw 20, to adjust quickly the opening S of the vice jaws according to the size of a workpiece. The movable body can be pushed so that the jaws 12,14 contact a work-piece 28.

(2) Next, the step for engaging the screw with the nut seat is described.

Turning the handle 1 in the right-hand direction (shown as arrow M in Fig. 3), to rotate the screw 20, drives also the ratchet sleeve 9 to the right through the guide key 16. The pawl 58 of ratchet sleeve 9 is in a pawl groove 53 of the cam 17, and the turning of the ratchet sleeve 9 causes the oblique surface 48 of the pawl 58 to bear against the oblique surface 49 of the pawl groove 53 (see the double-dash line in Fig. 14). Thus, under axial force from the compression spring 8 and the push of the oblique surface 48 of the ratchet sleeve 9, the cam also turns to the right, bringing its upward stroke curve to slide on the cam supporting surface 24 of the screw nut seat 19 until the positioning plane 51 of the cam 17 contacts with the limit surface 55 to stop the rotation (see Fig. 15). At the same time, the highest point 31 on the upward stroke curve of the cam 17 just touches the supporting surface 24 of the seat 19 and the screw 20 is lifted vertically along the parallel side walls 101 of holes 3,27 to a highest position. That is, the central axis of the screw 20 ascends vertically over an eccentricity distance "e" from its original position 0₂-0₂ to a position 0₁-0₁, until its outer threads 25 engage with the threads 15 in the holes 38 of the seat 19 so as to be relatively turnable (see Fig. 13).

(3) The step for clamping a workpiece (see Fig. 3) is now described.

Continue to turn the handle 1 along the righthand direction (M-direction). Since the positioning plane 51 of the cam 17 has touched the sidewall limit surface 55 of movable body 22 and stopped rotation of the cam 17 (see Fig. 15), the rotative force on the ratchet sleeve 9, applied to the oblique surfaces 48 and 49 of the contacting pawl 58 and pawl groove 53, generates an axial component along the direction "H". When that axial component is greater than the axial pressure of spring 8, the ratchet sleeve 9 displaces along the direction "H", until the pawl 58 leaves the pawl groove 53 and slides on the end surface 45 of the cam 17. Still continuing to turn the handle: since the outer screw threads 25 are engaged with the inner nut seat threads 15 of nut seat 19, and the seat 19 is fixed on the stationary body 21, the screw 20 moves forward along the axial direction "K" while turning to the right. Thus, the screw 20 pushes the movable body 22, through the end surface 60 on its left projection and the gasket 6, until the jaws 12,14 clamp the workpiece 28.

(4) The step for releasing a workpiece.

After the workpiece has been processed and requires to be removed, turning the handle 1 in a lefthand direction (N-direction, see Fig. 2) causes the screw 20 to rotate in the left-hand direction. Since the screw outer threads 25 are initially in engagement with the inner threads 15 of seat 19, the screw 20 displaces axially along the direction "H", and (through the gasket 42 and stop collar 43) pushes the movable body 22 along direction "H" causing the jaws to release the workpiece 28.

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

As the handle 1 turns to the left on release, the ratchet sleeve 9 driven by the screw 20 and guide key 16 also turns to the left until the pawl 58 falls into the pawl groove 53 (see Fig. 10) under the pressure of the compression spring 8. The screw 20 drives the ratchet sleeve 9 to continue its left turn, and turns the cam 17 in the lefthand direction through the abutting vertical surfaces 47 and 50 of the pawl 58 and pawl groove 53, moving the cam gradually to a released position, i.e., causing the lowest point 32 on the downward stroke to turn gradually to its lowest position (see Fig. 11) until the positioning projection 52 of cam 17 contacts with the horizontal limit plane 56. Thus the central axis of the screw 20 descends vertically from position 0₁ to position 0₂, dropping a height "e" and disengaging the screw outer threads 25 wholly from the inner seat threads 15. Now, the front and back ends of the screw 20 fall respectively on the lower supporting surfaces 36,37 of the supporting holes 7,23 of the front and back plates of the movable body 22 (see Fig. 8). Therefore, the screw 20 may displace forward or backward freely with the movable body 22 and 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 of the present invention, which is a bench vice for a tool and comprises a stationary body 63, a movable body 64, a screw 20, an eccentric cam 65, a screw nut seat 68, a one-way pawl pin 73, a ring extension spring 76, and a positioning pin 74. In this embodiment, the one-way pawl device has a pawl pin 73 instead of the ratchet sleeve 9 of the first embodiment. The movable body 64 can slide along the guide track in the stationary body 63, and the screw 20 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 a saddle, with an upper portion 88 (see Fig. 21), and is fixed on the stationary body 63 by means of bolts 75. The holes of the screw nut seat 68 are elongate, with two parallel side walls 87, an upper arc portion 86, and a lower arc portion with inner threads 15 suitable to engage with the outer threads 25 of the screw 20. The width of the elongate holes is substantially equal to the diameter of the screw 20. The eccentric cam 65 is located within the screw nut seat 68. The curve portion 92 of the eccentric cam 65 is circular and can slide between the upper cam support surface 94 and the lower cam support surface 95 of the nut seat 68. The eccentric cam 65 is provided on the plane 89 with a radial hole 67 and a threaded hole 90. It also has 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 the 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 80 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 pin 73. The screw 20 is provided in its axial direction with two pawl grooves 81 each having a vertical surface 83 and an oblique surface 82 (see Figs. 24 and 27). The front end plate of the movable body 64 is provided with two holes in which the spring 71 is located, to ensure that there is a gap "δ" between the front end wall and the gasket 70, and allow the screw 20 to have a little axial play so that a suitable engagement can be achieved. A gasket 93 is located on the inner side of the front end wall of the movable body and prevents the screw 20 from sliding off.
In case of releasing a workpiece (see Fig. 16), turning the screw 20 to the left (N-direction) causes the pawl pin 73 to fall into the pawl groove 81 of screw 20 under the action of ring extension spring 76. Thus, the screw 20 drives the eccentric cam 65 through two contacted vertical surfaces 83 and 79 respectively on the pawl groove 81 and the pawl 73 (see Fig. 24). The eccentric cam 65 rotates under the limit of two cam support surfaces 94 and 95 and causes the screw 20 to ascend vertically along 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 the screw 20 ascending from its lowest position 0₂-0₂ to its highest position 0₁-0₁. The threads 25 of the screw 20 disengage from the threads 15 of the nut seat 68 (see Fig. 22) so that the movable body 64 may be pushed or pulled manually and the opening "S" of the vice jaws can be adjusted quickly (see Fig. 16).
In clamping a workpiece, turning the screw 20 to the right (M-direction) causes the oblique surface 82 of the pawl groove 81 of screw 20 to bear against the oblique surface 78 of pawl pin 73 (see Fig. 27) and brings the eccentric cam 65 to rotate under the pull action of the ring extension spring 76, until the head of the positioning pin 74 contacts the upper limit surface 85 of the nut seat 68 (see Fig. 26). At the same time, the rotation of the eccentric cam 65 causes the screw 20 to descend along the parallel walls 87 of the elongate hole of the nut seat 68, with the axis of the screw 20 dropping from its highest position 0₁-0₁ to its lowest position 0₂-0₂, and the screw threads 25 engaging with the nut seat threads 15 (see Fig. 25). Continuing to turn the screw 20, the oblique surface 78 of pawl pin 73 slides over the oblique surface 82 of the pawl groove 81 of screw 20 when the component acting on the two oblique surfaces is greater than the extension force of the ring spring 76, so that the pawl pin 73 leaves the pawl groove 81 (see Fig. 27); then the screw 20 can turn continuously. Since the outer threads 25 of the screw 20 are engaged with the inner threads 15 of the nut seat 68 which is fixed on the stationary body 63, the screw 20 will move forward in the axial direction "K" while turning to the right, pushing the movable body 64 via the gasket 70 to clamp the workpiece.
Figs. 28-32 show a third embodiment of 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 in a guide hole 97 through the base 100 of the stationary body 63. The screw 20, supported in two holes of the end walls of the movable body 64, cannot move vertically up and down but can only turn, while the nut seat 60 can move vertically under the action of eccentric cam 65, so that the threads 25,15 of screw 20 and nut seat 68 may engage with or disengage from each other.
In case of clamping a workpiece, and turning the screw 20 along a righthand direction (M-direction), the screw 20 drives the eccentric cam 65 through the pawl groove and pawl pin 73. The eccentric cam 65 rotates under the limit of two surfaces 94 and 95, and causes the nut seat 68 to ascend vertically over a distance "h", because the screw 20 is fixed in the radial direction, (see Fig. 29, and Fig. 32). The nut seat threads 15 engage with the screw threads 25. Continuing to turn the screw 20, the pawl pin 73 slides out of the pawl groove of the screw 20. The screw 20 can then move along the axial direction "K" while it continues to turn to the right, and push the movable body 64 via the gasket 70 to clamp the workpiece (see Fig. 29).
In case of releasing a workpiece, turning the screw 20 to the left (N-direction), the screw 20 drives the eccentric cam 65 by the contacted vertical surfaces 83 and 79 respectively of the pawl groove 81 and the pawl pin 73. The cam 65 rotates to cause the nut seat 68 to descend vertically relative to the radially fixed screw 20, so that the threads 25 of the screw 20 disengage from the threads 15 of the nut seat 68 and the movable body can move freely in the axial direction (see Fig. 28).

Claims

A screw driven mechanism for two bodies which are relatively movable in a drive direction by rotating a screw (20) which extends axially in the drive direction, is axially constrained relative to a first one of the bodies (22,64), and engages a threaded nut seat (19,68) which is constrained in the drive direction relative to the second body (21,63);
comprising a thread engagement/disengagement mechanism wherein
the nut seat thread subtends not more that 180° so that the screw (20) can be relatively shifted transversely into/out of engagement therewith;
the screw (20) passes relatively rotatably through an eccentric member (17,65) which is mounted such that rotation of the eccentric member (17,65) can move the nut seat (19,68) and screw (20) into/out of threaded engagement, and
the eccentric member (17,65) is rotated by rotating the screw (20), being coupled thereto through a pawl connection which, when rotating the eccentric member (17,65) in the sense which brings the parts into threaded engagement, uncouples once a certain torque is exceeded so as to allow the screw to rotate without rotating the eccentric member;
characterised in that
the nut seat (19,68) has axially-spaced arms (40) with respective axially aligned slotted holes (38) through which the screw (20) passes, the slot elongation being in the direction of said transverse relative movement of the screw (20) and nut seat (19,68);
the eccentric member (17,65) is an eccentric cam positioned around the screw (20) between the arms (40) of the nut seat (17,65) and which has an outward cam surface which slidably engages a cam support surface (24,95) of the nut seat (19,68), and
the relative transverse movement which engages/disengages the thread is guided in one plane either by the nut seat (19,68) or by correspondingly slotted holes (7,23) in the first body (22), through which holes the screw extends.
A screw driven mechanism according to claim 1 in which the pawl connection comprises a sleeve (9) fitting around the screw (20) next to the eccentric cam (17) between the arms (40) of the nut seat (19), and constrained by a key (16) to rotate with the screw (20), the sleeve (9) being urged axially against the eccentric cam (17) by a spring (8), and a pawl (58) on the sleeve (9) being engageable in a ratchet recess (53) of the eccentric cam (17).
A screw driven mechanism according to claim 2 in which the ratchet recess (53) of the eccentric cam (17) has a circumferentially-facing stop surface (50) and an oblique sliding surface (49).
A screw driven-mechanism according to any one of claims 1 to 3 in which the eccentric cam has a stop projection (52) which meets a corresponding stop detent (56) of the first body (22) to prevent further rotation of the eccentric cam (17), after the threads disengage in the disengaging movement.
A screw driven mechanism according to claim 4 in which the eccentric cam (17) has an outward positioning plane (51) which contacts against a side surface of the first body (22) to maintain the cam member (17) in the position in which it holds the screw (20) in threaded engagement with the nut seat (19).
A screw driven mechanism according to any one of the preceding claims in which the nut seat (17) is a saddle fixed to the said second body (21) and the engagement/disengagement movement is guided in one plane by axially aligned slotted holes (7,23) through front and back parts of the first body (22), said slotted holes (7,23) having parallel side walls spaced substantially by the diameter of the screw (20), to guide the screw (20).
A screw driven mechanism according to any one of claims 1 to 5 in which the screw (20) is transversely fixed relative to the first body (64), and the engagement/disengagement movement is guided in one plane by a guided transverse movement of the nut seat (68) relative to the second body (63).
A screw driven mechanism according to claim 7 in which the nut seat is connected to the second body (63) by a guide pillar (96) which slides in a guide hole (97) in the second body (63).
A screw driven mechanism according to claim 1 in which the pawl connection between the screw (20) and eccentric cam member is by a pawl pin (73) comprised in the eccentric cam member (95) and spring-urged radially inwardly against the screw (20), which has a ratchet recess (81) for engagement by the pawl pin (73) so that the screw (20) and cam member (65) can rotate together.
A screw driven mechanism according to claim 9 in which the pawl pin (73) is slidable in a radial hole (67) in the cam member (65).
A screw driven mechanism according to any one of the preceding claims in which the slotted holes (38) of the nut seat arms (40) have circular arc sections at their extremities in the direction of their elongation, that at one extremity having threads (15) for engaging the screw (20), the other being without threads and having a larger radius than the screw (20) so as not to touch the screw (20) when the threads are disengaged.
A screw driven mechanism according to any one of the preceding claims in which the second body (21,63) is a stationary body, and the first body (22,64) is a movable body.
A bench vice, or tool incorporating a sliding table, comprising a screw driven mechanism according to any one of claims 1 to 12.