GB2272498A - A nut segment for an anti-backlash nut - Google Patents

Abstract

A nut segment 3 for an anti-backlash nut 1, said nut segment 3 having an internal threaded bore 7 adapted to receive a threaded member therein, and said nut segment having at least one resilient locking guide finger 21 thereon. In use each locking guide finger 21 interengages an elongate slot 13, 14 provided in a further nut segment 2, a lock stop 22 being provided at the end of each finger 21. <IMAGE>

Description

2272498 A NUr SEGMM FOP, AN ANTI-BACKLASH NUT

Background

This invention relates to an anti-backlash nut and more particularly to a linear positioning device where precise repe.,LL.,tl)iljty and accuracy is required. Specifically, the present invention encompasses elimination of backlash between a lead screw and mating nut through the use of.

a preload force applied by a spring through the nut mechanism.

Present devices reduce. backlash at the expense of increasing the frictional drafy. within the assembly.

Other devices use axial loading to bring portions of the nut into contact with portions of the screw thread face while another part of the nut contacts the opposite thread face to make tip for variations in lead screw thread variations and system wear. Some previous available designs use torsional springs, a large number of component parts, and/or an axially split nut thread.

of' nut assemblies utilizing axially split nuts are illustrated in United States Patent Nos. 4,131,031 and Re. 31,713. United States Patent No. 2,690,682 illustrates another type of anti-backlash nut which utilizes a pin and socket to prevent rotational movement between a pair of nut segments.

Brief Description

The present invention provides an anti-backlash lead screw nut which eliminates the drawbacks of previous designs and makes use of the concept that minimizes frictional drag. Its assembly is simple, being made up of only a small number of component parts. The nu. t has the capability of snapping into a fixed assembled condition.

Therefore, it does not have to be stored on its mating lead screw.

Wilen assembled the compression spring forces the forward part of the nut against the trailing face of the lead screw thread, and the rear portion of the nut against the leading face of the lead screw thread. The anti-backlash nut can be driven in either direction without any lost motion.

1 The juventIon Ims for one of its ol).iects m improved anti-backlash nut which is of simple construction, consisling of only two molded plastic nut parts and a st,1)1,1i.es the preload furce.

Another object of the present invention is the pi.ovision of an impi-oved anti-backlash nut in which assembly of the nul parts -xii(l spring is facilitated by built-in f ingers. No tools are required for as3ei)il)ly nor are any external holding devices needed after assembly.

Another ObJect of the present invention is the provision of an improved anti-backlash nut in which the parts are au Lomatica II y locked in place upon assembly.

Another object of the present invention is the pi.ovislon of an improved anti-backlash nut in which a relatively long axial compression spring gives essentially C(-oug -ance variations the 1( -c Ii the small (lisL, ass(""1)IY CTICOMIters of lead screw thread pitch iii,icctii.aci.es and ivear.

Another object of the present invention is the provision of an improved anti-backlash nut in which the level of preload force may be tailored when using th anti-backlash lead screw assembly in a specific design by choosing a spring with the desired spring constant.

Another object of the present invention is the provision of an improved anti-backlash nut in which there exists room for adjustment of the net which will allow additional spring compression to "fine tune" the desired preload.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

Description of the Drawing,

A preferred (iiiil)o(iiiiicril of Ihe invention has 1jeen chosen for purpose., of il l ustration and description and is shown in the accompanying drawings forming a part of the specification, wherein:

Fig. 1 is an exploded perspective view of the anti-backlash nut of the present invention.

Fig. 2 is a perspective view illustrating the assembled anti-backlash nut and the lead screw.

Fig. 3 is an exploded sectional view showing the nut segments of the present invention.

Fig. 4 is a sectional. view taken along line 4-4 of Fig. 2.

Fig. 5 is a sectional view similar to Fig. 4 showing the position of the anli-backlash nut of the present invention in a 6-6 of Fig. 5.

different position.

Fig. 6 is a sectional view taken along line Fig. 7 is.1 fragluenlary sectional view of the -backI,- and lead screw illu.strating anti ish nut.

the action of the compression spring applying an axial force to push apart the two nut segm n Ls.

Pesc.l.i)t.j()11 Referring to the drawings, the anti-backlash mil 1 of the presenl invention, comprises a female nut t2 and 111a1C Ilach nul segment 2 segmen 11111 SelTment 3.

and > 3 has a centi-al bore oj- opening 4 and 5, respectively, each of which has internal threads 6 and 7, respectively, with the same pitch as the thread 8 on a bolt or other member 53 lo be, inserled lite 1.ewi thin.

The female. nut segment 2 has a main hody portion 1,11 having a flange 3.0 extending upwardly therefrom at one end and at its other end has a hollow extension 11 with,tit utillireaded bore 12 which is of greater diameter Ilian the threaded bore 4. Thel, femitale. nut segment 2 is provided wit.ii a plurality of adjust.ment openings or slots 13 and 14. Preferably, the adjustment slot 14 is located in the hollow extension 11 arid lite adjustment slot 13 iS ill the hody portion 15 of the female nut segment 2, although the location of adjustment slots 13-14 may be changed if desired V.

Preferably, the adjusLment slots 13-14 are elongated although they may assump other shapes. It will also be noted that the adjustmenl slots 14 are shorter than the adjustment slots 13 an(] that adjustment slots 13-14 are linearly spaced from, but coextensive with, each other.

lit the drawings, a pair of adjustment slots 13-14 is shown as being localed di..teiteliicallY opposed to each other around the periphery or the ((!tii.t](-b nut selluxtent 2. flowever, it will be understood that any number of adjustable slots 1314 may be located around the periphery of the female nut segment 2 and that they need not be diametrically opposed to each other. lit addition, it is within the scope of the present Invention to use any number of coextensive adjustment slots raLlier than the pair 13-14 shown in the drawings.

The male stut segment 3 has a body portion 19 having an upstanding flange 20.extending upwardly from one end. The body portion 19 of the male nut segment 3 is insertable within the hollow extension 11 of the female nut segment 2. It will be noted that when the male nut 3 and the female nut 4 are in position, the inner threads 6 and 7 of both are coextensive with each other to accommodate the threaded bolt 9.

U"0M 111C 0111(31' Cild 01 Ilic, body portion cl j. 1111 19 of Ihe inale nut 3 are a plurality of guide prongs or fingers 21 each having a lock stop 22 thereon which are preferably located at the forward end of each guide finger 21. The guide lingrers 21 are preferably resilient so that if they are flexed in one direction tIWY will snaP back to their origirial positions. The lock stops 22 of these guide fingers 21 are narrow enough to enter the C> adjustment slots 13-14. Ttie, periphera-1. 1)o,z.",itions of the guide fingers 21 and lock stops 22 around the body portion 19 of the male nut segment 3 are the same as the peripheral positions of the adjustment slots 13-14 around the body portion 15 of the female nut segment 2.

Tile guide fingers 21 are of sufficient length so that the lock stops 22 enter the adjustment slots 13-3.4 when the male nut segment is inserted into the female nut segment 2. The'lock stops 22 are shown as being in the form of barbed books having inclined faces 23 and straight lock. surfaces 24 to lock the guide Singers in place in the adjustment slots 13-14.

l -g- The adjust-ment slots 13-14 are of different lengths with the linear lengths of each being longer than the linear lengths of the lock stops 22. This permits t_he lock stops 22 to be inserted into either of the adjustment slots 13-14 and permits the lock stops 22 to move lengthwise within each of the adjusIllient slots 1-3-14. The difference in length in the adjustment slots 13-14 will permit a greater amount of flexibility in adjusting or fine tuning the range within which the compression spring 25 wil exert a foree moving the two nut. segments 2-3 apart.

lf the lock stop 22 are in the shorter adjustment slots 14-; the range within which movement of the nut segments possible will be less than the range of movement when the lock stops 22 are in the longer adjustment slots 13.

The anti-backlaski nut of the present invention permits the flexibility needed in order to use the same nut for a wide variety of situations.

Preferably, 1he guide fingers 21 are shown in the drawings as being separate elements mounted in elongated retaining grooves 2G in the body portion 19 of male nut egment 3 and anchored at their rear in a slot 27 in the flange 20. This will hold the guide fingers 21 in place and prevent them from being misaligned. In addition, y elon[,,.itect guide grooves 28 and 29 are preferabl provided in the bores 12 and 4 of the extension 11 and body portion 15, respectively, of the female nut segment 3. These elongated guide grooves communicate with the adjustment slots 13 and 14 in order to positively direct the guide fingers 21 and lock stops 22 to the lock slots 1314 and prevent angular movement between two nut segments 2 and 3 when they are being assembled.

When the lock stops 22 are snapped into either of the adjustment slots 13-14, the nut segments 2-3 are locked together. The lock stops 22 protrude through the adjustment slots 13-14 and are captured therewithin so that the nut segments 2-3 cannot move rotationally in relation to each other and cannot become disassembled from each other when the anti-backlash nuL is in use.

W-Ii the parts in this position the threaded bolt 9 may i 11 be removed without the nut segments 2-3 becoming disassembled.

Ilence, the anti-backlash nut may be stored or shipped in its assembled condition without the threaded number 9. In order to disassemble the two nut segments 2-3 from each other, the protruding lock stops 22 must be depressed inwardly until they clear the inner edges of the walls of adjustment slots 13-14. This will free the lock stops 22 from the constraints of the adjustment slots 13-14 and permit the two nut segments 2-3 to be disassembled.

The same procedure is followed when it is desired to remove the lock stops 22 from one of the adjustment slots 13-14 and place them in another.

A spiral compression spring 25 is loosely positioned around both nut segments 2 and 3 and applies an outward force against the flanges 10 and 20 extending from each which bia'ses and 1110vo.s tlie L%vo nut segments 2 -and 3 apart and away from each other.

In operation, the male nut segment 3 is inserted into the female nut segment 2 by moving the guide fingers 21. along the grui(le irt-uoves 28-29 1111LIA. the lock stops 22 siiip into the openings 34 (for example), at which time the two nut segments 2 and 3 are held together against relative angular movement. The force of a spring 25 holds them apart by bearing against flanges 10-20. When the threaded member 9 is threacled into both nut segments 2-3, the parts will assume the positions shown in Figs. 2 and 4. If there is any wear or any other discrepancy between the threads 67 of the nut segments 2-3 and the thread 8 of the bolt 9, the spring-25 will allow the two segments to move apart relative to each other so that threads 6-7 of the nut segments 23 bear against the threads of the bolt 9.

When assembled the compression spring 25 forces the forward part of the threads 6 of nut segivient 3 against the trailing face of Che lead screw thread 8 and the rear portion of the threads 7 nul segincul 2 agrainst the leading face of the lead screw thread 8. This action is illustrated in Fig. 7 arid although Fig. 7 shows the lock stops 22 in the longer adjustment slots 13 (Fig. 5), the action is tlIf 1"11etib(31' GIC, JOCIC stops 22 are, In longer adjustment slots 13 (Fig. 5) or In shorter adjustment slots 14 (Fig.

4).

In the position of the parts shown in Fig. 4 with the lockstops 22 in the shorter adjustment slots 14, the two nut segments 2-3 can be fine tuned or adjusted, i.e., moved toward or away from each other to accommodate -for wear or other discrepancies in the threads. However, if a greater amount of fine tuning or adjustment is considered desirable or necessary, the-lock stops 22 can be Inserted into the longer adjustment slots 13 as shown in Fig. 5 to 7. In this position, a greater ailiount of fine tuning or adjustment can be exerted on the two nut segments 2-3 since the space wiLhin which the lock stops 22 move in adjustment slots 13 is greater.

With this construction, whenever the threads 6, 7 and 8 wear or there is any other discrepancy between the threads of threaded bolt 9 and the inner threads 6-7 of tile nut segments 2 and 3, the spring 25 moves the nut segments 2 and 3 apart and the threads 6, 7 and-8 remain in contact to compensate for the wear. lience, there is always a positive engagement between the nut segments 2 and 3 and the bo_11. 9.

With this structure, frictional drag is reduced to a minimum. Being made up of only three parts, the anti-backlash nut of the present invention has the capability of being snapped into a fixed assembled condition and will remain in that position so that it can be stored separate from its matIng lead screw. The antJ-backlash nut of the present invention can be easily driven in either direction without any lost motion whatsoever. The present invention provides an improved anti-backlash nut which is of simple construction which is easily assembled by the use of built-in guide fingers without the necessity of tools nor the necessity for any external holding devices to hold the parts together after assembly.

d As many and varied modifications of the subject matter of this invention will become apparent to those skilled in the art from the detailed description given hereinabove, it will be understood that the present invention is limited only as provided in the claims appended hereto.

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Claims (8)

1. A nut segment for an anti-backlash nut, said nut segment having an internal threaded bore adapted to receive a threaded member therein, said nut segment having a locking guide finger thereon.

2. A nut segment as claimed in claim 1, wherein said guide finger has a lock stop thereon.

3. A nut segment as claimed in claim 2, wherein a plurality of guide fingers are provided thereon.

4. A nut segment as claimed in claim 3, wherein said plurality of guide fingers are diametrically opposed to each other.

5. A nut segment as claimed in claim 4, wherein the guide fingers are resilient.

6. A nut segment as claimed in claim 5, wherein said guide fingers are mounted in retaining grooves.

7. A nut segment as claimed in claim 6, wherein said lock stops comprise inclined faces and lock surfaces.

8. A nut segment, as claimed in any preceding claim, substantially as hereinbefore described with reference to the accompanying drawings.