RU2390674C1 - Off-centre screw gear - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: off-centre screw gear consists of case, of nut installed in case on bearing supports and of screw passing inside of nut with eccentricity "e". The screw is made curvilinear concentric to its curved axial line; it has pitch of alternate size proportional to radius of curvature. Also the screw is installed with alternate eccentricity relative to nut axis, the biggest in zone of least space between the screw and the nut. Additionally, the screw can be of closed circular shape, for example torus. Balls can be placed in threaded grooves of the screw and nut.

EFFECT: facilitation of nut rotation conversion into circular or curvilinear motion of screw.

5 dwg

Description

The present invention relates to the field of mechanical engineering, to mechanisms for transforming movements, specifically converting rotation into circular or curvilinear motion of various technological devices.

Known eccentric helical gear containing a housing mounted in it with the possibility of rotation of a nut of constant diameter and a screw whose axis is eccentric to the axis of the nut [1]. This transmission converts the rotation of the screw into a rectilinear translational motion of the nut, but is not suitable for transmitting motion along a curved path, for example, along a straight line passing into an arc.

Known eccentric helical gear, in which the nut is installed in the housing through an intermediate eccentric sleeve, which allows you to adjust the eccentricity and contact areas of the turns of the screw and nut [2]. This gear also does not allow the rotation to be converted into curved motion.

Known ball screw mechanism in which the screw is made of variable pitch [3]. The mechanism allows you to get a variable speed of the screw with a uniform rotation of the nut, but is not suitable for transmitting motion along a path curve.

The technical result of the proposed transmission is to convert the rotation of the nut into a circular or curved movement of the screw or the nut itself relative to the fixed screw. The indicated technical result is achieved in that the screw is made in a curved shape concentric with its curved center line, has a step of a variable value proportional to the radius of curvature of the shape, and is set relative to the axis of the nut with a variable eccentricity having the largest value in the zone of the smallest distance between it and the nut.

The shape of the screw can be closed annular, for example in the form of a circular torus, or open, with an axis of variable curvature and direction, for example, a sinusoid, in the form of a round sinusoid. The thread pitch of the screw is equal to the pitch of the nut in a plane perpendicular to the smallest distance between them and passing through the axis of the nut. In the threaded grooves of the screw and nut, balls can be placed, the number of which is proportional to the length of the nut groove along the average thread diameter, and the gap compensator between them.

Figure 1 shows an eccentric helical gear with a screw in the form of a torus; figure 2 is a section aa in figure 1 and the various positions of the screw relative to the nut (dash-dot); figure 3 - helical gear with a screw having a sinusoidal axis and the displacement of the screw relative to the nut (dash-dot); 4 and 5 are longitudinal sections of a slip transmission and a ball screw transmission on a nut, respectively.

The eccentric screw transfer comprises a housing 1, a nut 2 installed in it on the bearings 3 and a screw 4 passing inside the nut with an eccentricity “e” (Figs. 1, 2). The screw is made curved, concentric with its curved center line "a". According to its curvature, it can take the form of a round torus 4 with constant curvature of the axial line with one center 0 of curvature - a circle (see figure 1); with variable curvature in the magnitude of the axis and direction, for example, an ellipse - an elliptical torus, a screw with an axis of a sinusoid 5 (Fig.3) and others. The screw 4 in the form of an annular torus can occupy various positions relative to the nut within 360 ° (see figure 2, dash-dot).

.The thread pitch P of the screw has a variable value proportional to the radius of curvature of the mold. With regard to the helical torus, the outer thread pitch P refers to the inner P _i , as the outer R and inner R _{i are the} average radii of its thread (see figures 1, 4):

.

The screw eccentricity with respect to the nut is variable due to the curvature of the screw center line. The greatest eccentricity "e" - the distance between the tangent to the axial line of the bend of the screw and the axis of the nut is located on the line of the smallest distance between the screw and the nut (Figs. 4, 5). In this zone, the most tight contact of the threads of the screw and nut takes place.

The thread profile of a screw helical gear can be different: triangular, trapezoidal, round and others, with the exception of a rectangular one. To reduce the screw pitch error from the nominal nut pitch P _{g, the} thread pitch P _{0 of the} screw is taken to be equal to the pitch P _g on the radius of the greatest curvature of the screw center line; in relation to the torus - on a radius R _{0 of the} circumferential axial line: P _about = P _g . Then the error of the external P and internal P _{i of the} thread pitch of the screw is ΔР = ± P _r r ₀ / R ₀ , the sign + (plus) for the external step; r ₀ - the average radius of the thread of the screw (see figure 1).

The greatest number of contact pads, and therefore the highest accuracy of movement in eccentric helical curved gears, is a ball gear. In the threaded grooves of its screw 7 and nut 6, balls 8 are placed, the number of which is proportional to the length of the groove along the average diameter of the nut d (Fig. 5). The nut has a liner 9 with a bypass channel for balls. To compensate for the accumulated along the length of the turns of the gap of the balls due to the variable depth of the grooves along the contact helix, there is a compensator 10 in the form of a washer of antifriction material. The compensator provides a closed screw pillar of balls. It can have various designs, such as springs. You can use well-known designs to select clearances in ballscrews.

The drive in eccentric curved helical gears is a nut. Reverse rotation from a curved screw to a nut is not possible. Therefore, the nut is equipped with a ring gear 11, which can be mounted (see figure 5) or made in one piece with the nut (see figure 4).

For assembling a closed helical gear with a screw in the form of a torus, an insert sector 12 is intended, which, after screwing on the nut, is installed in its place in the open section of the screw and fixed in a known manner, for example by gluing (see figure 1).

The operation of the helical gear is as follows. The housing 1 of the nut is attached to the gearbox (not shown), and its ring gear 11 engages with the drive gear of the gearbox (see Figures 4, 5). From it, the nut receives rotation and rotates the ring screw - torus 4 (see Fig. 1) or reports movement along a curved path - a sinusoid to a screw in the form of a round sinusoid 5 (see Fig. 3, dash-dot). With a fixed screw, the nut itself receives the corresponding movement. To do this, the gearbox supporting it has circular guides, if the screw is a torus, or mounted on a cross table with mutually perpendicular rectilinear guides, if the screw is a round sinusoid.

.An example of an eccentric helical transmission slip (figure 4). The nut has a trapezoidal thread with an angle of profile α = 40 °, pitch of turns P _g = 10 mm, working height of the profile H ₁ = 5 mm. A screw in the shape of a circular torus has an average thread radius r ₀ = 16 mm, a radius of the circumferential center line R ₀ = 100 mm, a thread pitch equal to a nut pitch of 10 mm on the radius of the center line. The smallest eccentricity of the curved screw relative to the axis of the nut is determined

.

, наименьший эксцентриситет

. При эксцентриситете е=2,2 мм средний диаметр резьбы гайки равен d=36,4 мм.The error of the outer pitch of the screw is

smallest eccentricity

. With an eccentricity of e = 2.2 mm, the average diameter of the nut thread is d = 36.4 mm.

Eccentric helical gear with curved screw

axis, will find application in instrumentation, machine tools, such as rotary tables; mechanisms of transformation of movements, in copying devices.

Information sources

1. Kozhevnikov S. N. and other mechanisms. Directory. 4th ed.-M.: Mechanical Engineering, 1976 .-- 784 p. Fig. 2.251, p. 138.

2. A.S. USSR No. 1350420, IPC F16H 25/22, Eccentric helical gear. 1987. Prototype.

3. A.S. USSR No. 292045, IPC F16H 25/22, Ball screw mechanism. 1971.

Claims (5)

1. An eccentric helical gear, comprising a housing, a nut rotatably mounted therein, and a screw, the axial line of which is eccentric to the axis of the nut, characterized in that the screw is made in a curved shape concentric with its curved axial line, has a variable pitch proportional to the radius of curvature , and is installed relative to the axis of the nut with a variable eccentricity, the largest in the zone of the smallest distance between the screw and the nut. 2. The helical gear according to claim 1, characterized in that the screw has a closed annular shape, for example a torus. 3. The helical gear according to claim 1, characterized in that the screw has an open curved shape with an axis of variable curvature and direction, for example, a sinusoid. 4. The helical gear according to claim 1, characterized in that the thread pitch of the screw is equal to the thread pitch of the nut in a plane perpendicular to the smallest distance between them and passing through the axis of the nut. 5. The helical gear according to claim 1, characterized in that in the threaded grooves of the screw and nut are placed balls, the number of which is proportional to the length of the groove along the average diameter of the nut, and a gap compensator in ball coils.

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