GB2088518A

GB2088518A - Screw-and-nut gearing in servo drives

Info

Publication number: GB2088518A
Application number: GB8134180A
Authority: GB
Original assignee: Elektrowatt AG
Current assignee: Siemens Building Technologies AG
Priority date: 1980-11-28
Filing date: 1981-11-12
Publication date: 1982-06-09
Also published as: CH649356A5; DE3143580C2; DK526581A; DE3143580A1; SE8106584L

Abstract

An externally-threaded adjusting spindle 11 secured against twisting is screwed into a female element 12 which is coupled to a motor 17 via a slipping clutch and a transmission and may be driven thereby. To isolate the internal screw thread of the female element 12 from the actions of the bending moments acting on the adjusting spindle 11, the adjusting spindle 11 is com- plementarily installed in longitudinally displaceable manner in bearing members 20,21 co-axially secured with respect to the female element at each end thereof. <IMAGE>

Description

SPECIFICATION Improvements in or relating to servo drives The present invention relates to servo drives comprising an externally-threaded adjustable spindle secured against twisting, which is screwed into a female element coupled to a motor via a slipping clutch and a transmission and is drivable thereby.

Hereinafter such a servo drive will be referred to as "of the kind described".

Servo drives of the kind described have been disclosed, for example in the Swiss patent specification No. 601,744. The purpose of the slipping clutch limiting the torque transmitted consists in that the motor driving the female element via the transmission gear need not be switched off via limit switches actuated by the adjusting element, which may be for example a flap or slider, actuated by the adjusting spindle, has reached one of its terminal positions.

This also eliminates the need for adjusting such limit switches upon installing the servo drive in situ.

Furthermore, this ensures that the adjusting member is held in its terminal positions with a force which, under consideration of the transmission ratios within the transmission gear and/or between the female element and the adjusting spindle, depends on the response torque of the slip clutch.

In the known servo drives, the female element is commonly formed integrally from plastics material or from another material requiring no, or only infrequent, lubrication, whereas the adjusting spindle is commonly formed from steel.

The stress on the adjusting spindle is purely axial in the most infrequent cases only, in particular at the terminal positions of the adjusting member but also at its intermediate positions. This has the consequence that the female element and in particular its internal screw thread has to bear not only purely axial forces but also such as tend to skew the adjusting spindle within the female screw thread, i.e.

such as exert a bending movement on the adjusting spindle.

If the servo drive then remains in an identical position for a protracted period, in particular at one of the terminal positions of the servo drive whilst the motor continues to run, the female screw thread of the female element may be deformed gradually by cold deformation. This may lead to jamming of the adjusting spindle in the female element during the next displacement of the drive, or else at least to excessive play of the adjusting spindle within the female element.

Consequently it is an object of the invention to provide a servo drive of the kind described, which avoids or minimises the disadvantages referred to.

Accordingly, the invention consists in a servo drive of the kind described, wherein the adjusting spindle is arranged in longitudinally displaceable manner in a bearing member which is co-axially secured with respect to the female element, at least at its one egress side from the latter.

In order that the invention may be more clearly understood reference will now be made to the accompanying drawings which show some embodiments thereof by way of example and in which: Figure 1 shows a first embodiment, partially in cross-section through an axial plane of the adjusting spindle, and Figure2 shows a modified embodiment in a mode of iilustration analogous to that of Figure 1.

Referring now to the drawings, the servo drive 10 illustrated in Figure 1 comprises an externally threaded adjusting spindle 11 which is secured against twisting by means which are not illustrated.

The adjusting spindle is screwed into a female element 12 which is integrally formed as the hub of a gearwheel 13. The gearwheel 13 is the final member of a reduction gear installed in a housing 14 and is rotatably journalled therein by means of two bearings 15, 16. A motor 17, for example a synchronous motor comprising a built-in magnetic clutch (not illustrated) is flange-coupled to the housing 14 as the slipping torque limiting clutch, said motor element 12 in the one direction of rotation or the other.

Two co-axial bearing sockets 18,19 surrounding the adjusting spindle 11 are provided on the housing 14. A metal bearing bushing 20 and 21 respectively, surrounding the adjusting spindle 11 in a sliding fit and consisting of hardened steel for example, is pressed into each of the bearing sockets 18,19. The bearing bushings 20,21 which are co-axial to the female element 12 offer no impediment to a longitudinal displacement of the adjusting spindle 11, but effectively absorb bending moments acting thereon so that the female screw thread of the female element 12 is relieved of this stress.

The spacing of the bearing bushings 20,21 from each other, or the length of the bearing sockets 18,19 are arranged to be of such size as is appropriate to the requirements of use. The spacing of the bearing bushings 20,21 which is fixed in this case, from each other may for example amount to 1.5 - 2 times the length of the female element 12 provided with the female screw thread.

The embodiment shown in Figure 2 differs from that of Figure 1 in that the female element 12 forming the hub of the gearwheel 13 is extended at both extremities beyond the middle section having the internal screw thread. These extensions are marked 18' and 19'. The bearing bushings 22 and 21 are not pressed into bearing sockets formed in unit with the housing 14 in this case, but into the extensions 18' and 19'. In this embodiment, the bending moments acting on the adjusting spindle 11 are not borne direct by the housing 14 but first via the gearwheel 13 as a whole and are carried on the housing 14 via its bearings 15,16. The internal screw thread present between the bearing bushings 20,21 nevertheless remains largely unaffected by forces deriving from such bending moments.

1. A servo drive of the kind described, wherein the adjusting spindle is arranged in a longitudinally displaceable manner in a bearing member co-axially secured with respect to the female element at least at its one egress side from the later.

2. A servo drive as claimed in claim 1,wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to servo drives The present invention relates to servo drives comprising an externally-threaded adjustable spindle secured against twisting, which is screwed into a female element coupled to a motor via a slipping clutch and a transmission and is drivable thereby. Hereinafter such a servo drive will be referred to as "of the kind described". Servo drives of the kind described have been disclosed, for example in the Swiss patent specification No. 601,744. The purpose of the slipping clutch limiting the torque transmitted consists in that the motor driving the female element via the transmission gear need not be switched off via limit switches actuated by the adjusting element, which may be for example a flap or slider, actuated by the adjusting spindle, has reached one of its terminal positions. This also eliminates the need for adjusting such limit switches upon installing the servo drive in situ. Furthermore, this ensures that the adjusting member is held in its terminal positions with a force which, under consideration of the transmission ratios within the transmission gear and/or between the female element and the adjusting spindle, depends on the response torque of the slip clutch. In the known servo drives, the female element is commonly formed integrally from plastics material or from another material requiring no, or only infrequent, lubrication, whereas the adjusting spindle is commonly formed from steel. The stress on the adjusting spindle is purely axial in the most infrequent cases only, in particular at the terminal positions of the adjusting member but also at its intermediate positions. This has the consequence that the female element and in particular its internal screw thread has to bear not only purely axial forces but also such as tend to skew the adjusting spindle within the female screw thread, i.e. such as exert a bending movement on the adjusting spindle. If the servo drive then remains in an identical position for a protracted period, in particular at one of the terminal positions of the servo drive whilst the motor continues to run, the female screw thread of the female element may be deformed gradually by cold deformation. This may lead to jamming of the adjusting spindle in the female element during the next displacement of the drive, or else at least to excessive play of the adjusting spindle within the female element. Consequently it is an object of the invention to provide a servo drive of the kind described, which avoids or minimises the disadvantages referred to. Accordingly, the invention consists in a servo drive of the kind described, wherein the adjusting spindle is arranged in longitudinally displaceable manner in a bearing member which is co-axially secured with respect to the female element, at least at its one egress side from the latter. In order that the invention may be more clearly understood reference will now be made to the accompanying drawings which show some embodiments thereof by way of example and in which: Figure 1 shows a first embodiment, partially in cross-section through an axial plane of the adjusting spindle, and Figure2 shows a modified embodiment in a mode of iilustration analogous to that of Figure 1. Referring now to the drawings, the servo drive 10 illustrated in Figure 1 comprises an externally threaded adjusting spindle 11 which is secured against twisting by means which are not illustrated. The adjusting spindle is screwed into a female element 12 which is integrally formed as the hub of a gearwheel 13. The gearwheel 13 is the final member of a reduction gear installed in a housing 14 and is rotatably journalled therein by means of two bearings 15, 16. A motor 17, for example a synchronous motor comprising a built-in magnetic clutch (not illustrated) is flange-coupled to the housing 14 as the slipping torque limiting clutch, said motor element 12 in the one direction of rotation or the other. Two co-axial bearing sockets 18,19 surrounding the adjusting spindle 11 are provided on the housing 14. A metal bearing bushing 20 and 21 respectively, surrounding the adjusting spindle 11 in a sliding fit and consisting of hardened steel for example, is pressed into each of the bearing sockets 18,19. The bearing bushings 20,21 which are co-axial to the female element 12 offer no impediment to a longitudinal displacement of the adjusting spindle 11, but effectively absorb bending moments acting thereon so that the female screw thread of the female element 12 is relieved of this stress. The spacing of the bearing bushings 20,21 from each other, or the length of the bearing sockets 18,19 are arranged to be of such size as is appropriate to the requirements of use. The spacing of the bearing bushings 20,21 which is fixed in this case, from each other may for example amount to 1.5 - 2 times the length of the female element 12 provided with the female screw thread. The embodiment shown in Figure 2 differs from that of Figure 1 in that the female element 12 forming the hub of the gearwheel 13 is extended at both extremities beyond the middle section having the internal screw thread. These extensions are marked 18' and 19'. The bearing bushings 22 and 21 are not pressed into bearing sockets formed in unit with the housing 14 in this case, but into the extensions 18' and 19'. In this embodiment, the bending moments acting on the adjusting spindle 11 are not borne direct by the housing 14 but first via the gearwheel 13 as a whole and are carried on the housing 14 via its bearings 15,16. The internal screw thread present between the bearing bushings 20,21 nevertheless remains largely unaffected by forces deriving from such bending moments. CLAIMS

2. A servo drive as claimed in claim 1,wherein the bearing member is located at the egress side of the adjusting spindle.

3. A servo drive as claimed in claim 1, in which the female element is the hub of a transmission installed in a housing, wherein a bearing sleeve for the adjusting spindle is installed in one bearing socket formed on the transmission housing at both egress sides of the adjusting spindle out of the female element.

4. A servo drive as claimed in claim 1, in which the female element is the hub of a gearwheel forming the final member of a transmission, wherein a bearing sleeveforthe adjusting spindle is installed in one of the two terminal axial portions of the hub.

5. A servo drive as claimed in claim 1, in which the female element is the hub of a gearwheel forming the final member of a transmsission, wherein a bearing sleeve for the adjusting spindle is installed in each of the two axial terminal portions of the hub.

6. A servo drive as claimed in claim 1, wherein the bearing element is of metal.

7. A servo drive as claimed in claim 6, wherein the metal bearing element is hardened.

8. A servo drive, substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

9. A servo drive, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.