DE202013009833U1 - Electric cylinder with force sensor - Google Patents

Abstract

Electric cylinder (10) with a housing (12) in which a threaded spindle (14) is rotatably mounted with respect to a longitudinal axis (11), wherein the threaded spindle (14) is surrounded in sections by a cantilever (20), which with a first end ( 21) in the direction of the longitudinal axis (11) protrudes from the housing (12), wherein it is provided at the opposite second end (22) with a nut (30) which engages in the threaded spindle (14), wherein the nut (30) with respect to the longitudinal axis (11) relative to the housing (12) with a rotation (15) is secured against rotation, wherein at the first end (21) of the boom (20) a ball joint head (50) with a bearing bore (51) is arranged the electric cylinder (10) comprises a force sensor (60), characterized in that the force sensor (60) by a separate bolt (40) is formed, which passes through the bearing bore (51) of the ball joint head (50).

Description

The invention relates to an electric cylinder according to the preamble of claim 1.

A known electric cylinder comprises a housing in which a ball screw spindle is rotatably mounted with respect to a longitudinal axis via radial rolling bearings. Away from the pivot bearing, the threaded spindle is surrounded by a tubular arm, which protrudes with a first end of the housing. At the opposite second end of the boom with a ball screw nut is firmly connected, which engages with their endless rotating balls in the threaded spindle. Further, an anti-rotation device is provided, which comprises a slide strip, which is fixedly connected to the mother, wherein it runs in a groove extending along the longitudinal axis in the housing. Thus, the mother can not be rotated relative to the housing with respect to the longitudinal axis. Further, a separate force sensor is provided, which has a ball joint head with a bearing bore, wherein the force sensor is attached to the first end of the boom.

The disadvantage of this electric cylinder is that the force sensor increases the overall length of the electric cylinder in the direction of the longitudinal axis.

According to the independent claim, an electric cylinder according to the invention is characterized in that the force sensor is formed by a separate bolt which passes through the bearing bore of the ball joint head. Such an electric cylinder has a short length.

In the dependent claims advantageous refinements and improvements of the invention are given.

The nut may have an inner profiling, wherein a plurality of separate planetary rollers are provided with an outer profiling, which engage both in the inner profiling of the nut and in the threaded spindle. The inner and the outer profiling are preferably each a thread with helical profile grooves, which have an opposite pitch direction, so that the planetary rollers do not move in the longitudinal direction relative to the remaining nut when they roll on the inner profiling. Such a planetary screw drive can transmit particularly high forces, in particular significantly higher forces than a ball screw. The force sensor according to the invention is able to absorb and measure these forces. In the inner and / or outer profiling but it can also be endless circumferential tread grooves.

There may be provided a first and a second fork leg, between which the ball joint head is arranged, wherein the bolt also passes through the first and the second fork legs. The entire force acting in the direction of the longitudinal axis of the electric cylinder is transmitted via the bolt so that it can be measured accurately. The first and second fork legs are preferably part of a one-piece forked bearing block.

The bolt may comprise a transformer having at least one primary and at least one secondary coil, which are penetrated by a common ring core, wherein the toroidal core is connected to the bolt so that it is elastically deformed when a force acting in the direction of the longitudinal axis on the Bolt acts. In order to measure the force acting on the bolt, an alternating voltage is fed into the at least one primary coil which induces in the at least one secondary coil an alternating voltage whose amplitude depends on the shape of the toroidal core. For this purpose, the toroidal core may in particular have a gap whose width changes due to the action of force.

The bolt may be provided with at least one ohmic resistance element which is connected to the bolt such that it is elastically deformed when a force acting in the direction of the longitudinal axis acts on the bolt. The ohmic resistance element may be a strain gauge or a thin film coating. A force-induced change in shape of the resistance element causes a change in its ohmic resistance. Preferably, a total of four resistive elements are provided, which are interconnected in the form of a bridge circuit to minimize temperature effects in the force measurement.

The bolt may have a first, a second and a third section, wherein the third section passes through the bearing bore, wherein the third section is connected to the first section via at least one first bending beam, wherein it connects to the second section via at least one second bending beam wherein the first and the second bending beam have a lower bending stiffness than the first, the second and the third section, wherein the at least one resistance element is fixedly connected to the at least one first and / or the at least one second bending beam. Due to the action of force on the bolt occurs on the bending beam on a sufficiently large elastic strain or compression, which can be measured well with the resistance element. The shape of the bending beam can at the same time be easily designed so that from the measured strain the acting force can be calculated exactly.

The first section can pass through the first fork leg, wherein the second section passes through the second fork leg. The bending beams are thus not involved in the load transfer to the bearing bore or the fork legs, so that the force measurement is not affected thereby.

The bearing bore may be formed circular cylindrical, wherein it is perpendicular to the longitudinal axis, wherein preferably the first, the second and the third portion are also formed circular cylindrical. Such an electric cylinder is particularly easy to produce. However, the proposed shape causes the bolt can rotate. This is no longer sure that the force acting exactly opposite the bolt has the optimal direction for the force measurement. The solution to this problem will be discussed below.

The anti-rotation device can be arranged at one end of the housing, on which the boom emerges from the housing. The anti-rotation causes primarily that the corresponding torque does not have to be absorbed by the bolt. This would falsify the result of the force measurement. The proposed arrangement of the rotation of the bolt is best relieved of said torque.

The bolt may have a groove with a bottom surface which extends transversely to the bolt, wherein at least one separate plate is provided, which engages in the groove, wherein it rests with a flat edge surface on the bottom surface. The plate on the one hand causes the bolt can not rotate with respect to the central axis of the bearing bore. Next prevents the plate that the bolt moves in the direction of the central axis of the bearing bore.

The at least one plate may be attached to the first or the second fork leg and preferably screwed thereto. Such an electric cylinder is particularly inexpensive.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

1 a perspective view of an electric cylinder according to the invention;

2 a partial exploded view of an electric cylinder according to the invention in the region of the first end of the boom;

3 a front view of a bolt according to the invention; and

4 a cross section of the engagement between the nut and the threaded spindle.

1 shows a perspective view of an electric cylinder according to the invention 10 , The housing 12 of the electric cylinder 10 includes a main body 17 in the form of a with respect to a longitudinal axis 11 circular cylindrical steel tube is formed with a constant wall thickness. Inside the main body 17 is a threaded spindle 14 taken from the in 1 only the circular cylindrical drive pin can be seen. At one end of the body 17 is a separate pivot bearing 13 for the threaded spindle 14 attached so that the threaded spindle 14 with respect to the longitudinal axis 11 is rotatable. The pivot bearing 13 preferably comprises a plurality of radial roller bearings, in particular angular contact ball bearings. The opposite end of the threaded spindle 14 where the helical thread grooves are provided protrudes into the interior of the cantilever 20 into it and is there in the case of very long threaded spindles 14 slidably supported.

At the boom 20 it is also a respect to the longitudinal axis 11 circular cylindrical steel tube with constant wall thickness. The boom 20 however, is on its outside with a total of four flats 23 provided so that when viewed in cross section, a square with rounded corners results. At the flattenings 23 is the anti-twist device 15 positively, so that the boom 20 with respect to the longitudinal axis 11 not opposite the case 12 twisting kenn. The anti-twist device 15 is at the end 16 of the housing, on which the boom 20 protrudes from this. The anti-twist device 15 is preferably according to DE 10 2011 116 631 A1 whose entire content is referred to and incorporated in the present application.

At the first end 21 of the jib 20 that outside the case 20 is arranged, is a threaded pin 24 fixed, which extends along the longitudinal axis. At this threaded pin 24 a ball joint head (not shown) fixed with respect to 2 will be explained in more detail. At the opposite second end 22 of the jib 20 that is inside the main body 17 of the housing 12 is located, a nut is arranged, in screw engagement with the threaded spindle 14 stands. This screw engagement is related to 4 explained in more detail.

2 shows a partial exploded view of an electric cylinder according to the invention 10 in the area of the first end 21 of the jib 20 , There is a ball joint head 50 on the threaded pin (No. 24 in 1 ) screwed. By means of the two clamping screws 56 can the ball joint head 50 in any rotational position with respect to the longitudinal axis 11 be clamped. The ball joint head 50 includes a ball joint with a circular cylindrical bearing bore 51 whose central axis 55 in the middle position of the ball joint exactly perpendicular to the longitudinal axis 11 is aligned. In any case, the central axis intersects 55 the longitudinal axis 11 , The ball joint should be a bending stress of the bolt 40 be avoided, which distorts the force measurement. It should be noted that the present electric cylinder 10 can produce very large forces, despite the massive design of the electric cylinder 10 lead to a noticeable elastic deformation. This deformation can be compensated by the mobility of the ball joint, without causing unwanted tension.

On both sides next to the ball joint head 50 is ever a first and a second fork legs 52 ; 53 arranged, which is part of a one-piece fork bearing block 54 are. The fork bearing block 54 has, for example, four mounting holes on a base plate 57 via which it can be screwed to a (not shown) parent assembly.

The bolt 40 passes through the first and second fork legs 52 ; 53 each in a circular cylindrical bore. Next penetrated by the bolt 40 the bearing bore 51 in the ball joint head 50 , The bolt 40 has for this purpose a first, a second and a third circular cylindrical section 41 ; 42 ; 43 on. The third section 43 is with very little clearance to the bearing bore 51 adapted and is located there. The first and the second section 41 ; 42 lie on the first and on the second fork leg 52 ; 53 at. The third section 43 is over two first bending beams 44 integral with the first section 41 connected. Next is the third section 43 over two second bending beams 45 connected to the second section. The diameters of the first, second and third sections 43 are identical.

At the outer edge of the first and second sections 41 ; 42 is each a groove 46 provided, which is perpendicular to the central axis of the bolt 40 extends. The groove 46 has two parallel, flat side surfaces and a flat bottom surface 47 on. In at least one of the grooves 46 grab a flat plate 70 with a constant thickness, with an edge surface 71 the overall rectangular plate 70 at the bottom surface 47 the associated groove 46 is applied. The plate 70 For example, it will be two screws 72 interspersed, which are presently designed as a cylinder head bolts. The screws 72 are in the plate 70 associated first and second fork legs 52 ; 53 screwed in, taking the plate 70 on the outside of said fork leg 52 ; 53 is applied.

Attention is still on the transmitter 48 which inside the stud 40 is arranged and at which the force sensors (no. 60 in 3 ) are connected. Via the socket 49 can the transmitter 48 For example, be connected to a (not shown) machine control.

3 shows a front view of a bolt according to the invention 40 , wherein the viewing direction in 2 is marked accordingly. The third section 43 is over two first bending beams 44 integral with the first section 41 connected. Next he is over two second bending beam 45 integral with the second section 42 connected. The bending beam 44 ; 45 each have a significantly lower bending stiffness than the first, the second and the third section, since the respective cross-sectional area is significantly smaller. On each of the bending beams 44 ; 45 , preferably on the protected inside, is in each case a resistance element 61 attached, which in the present case is designed as a strain gauge. The ohmic resistance elements 61 are present on the associated bending beam 44 ; 45 glued so that they are subjected to the same elastic deformation as the bending beam 44 ; 45 , It is also possible the resistor elements 61 in the form of a thin film coating on the bending beam 44 ; 45 applied.

The four ohmic resistance elements 61 are interconnected in a bridge circuit. Accordingly, they are connected in an annular manner in series. Thereby define two immediately adjacent resistance elements 61 each a bridge node 62 ; 63 ; 64 ; 65 , To two opposite bridge nodes, for example the first and the third bridge node 62 ; 64 , is from the transmitter 48 an electrical voltage applied. At the remaining two opposite bridge nodes, here the second and the fourth bridgehead 63 ; 65 this results in an electrical voltage, which from the transmitter 48 is measured. The result of the measurement becomes the one on the bolt 40 attacking joint force 66 determined and in a suitable form on the socket 49 output. The evaluation electronics 48 is doing over the socket 49 also supplied with electricity. It should be noted that the two fork forces 67 due to the geometric structure of the electric cylinder are exactly half the size of the joint force 66 , pointing in the opposite direction.

4 shows a cross section of the engagement between the nut 30 and the threaded spindle 14 , The mother is doing with an internal profiling 31 provided, preferably in the form of with respect to the longitudinal axis 11 formed helically extending thread grooves, which most preferably have a pointed profile. Preferably, a multi-start thread is provided. At the inner profiling 31 For example, eight identical planetary rollers roll 32 spread uniformly over the circumference of the nut 30 are arranged. The planetary roles 32 are preferably kept at a distance via a cage (not shown). The planetary roles 32 are with a to the internal profiling 31 mother 30 adapted external profiling 33 provided, which is preferably formed in the form of helically extending thread grooves. The pitch, the number of gears and the pitch direction is preferably selected so that the planetary rollers 32 in the direction of the longitudinal axis 11 not to the mother 30 move as they roll on this. It is also possible that the inner and the outer profiling 31 ; 33 is formed in the form of annular circumferential grooves.

LIST OF REFERENCE NUMBERS

10

electric cylinders

11

longitudinal axis

12

casing

13

pivot bearing

14

screw

15

twist

16

End of the housing on which the boom emerges

17

body

20

boom

21

first end

22

second end

23

flattening

24

threaded pin

30

mother

31

internal profiling

32

planetary roller

33

outside profiling

40

bolt

41

first section

42

second part

43

third section

44

first bending beam

45

second bending beam

46

groove

47

floor area

48

evaluation

49

receptacle

50

Ball joint head

51

bearing bore

52

first fork leg

53

second fork leg

54

Fork bearing block

55

Center axis of the bearing bore

56

clamping screw

57

mounting hole

60

force sensor

61

resistive element

62

first bridge node

63

second bridge node

64

third bridge notes

65

fourth bridge node

66

joint power

67

fork force

70

plate

71

Edge surface of the plate

72

screw

73

inner thread

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011116631 A1 [0022]

Claims (11)

Electric cylinder ( 10 ) with a housing ( 12 ), in which a threaded spindle ( 14 ) with respect to a longitudinal axis ( 11 ) is mounted rotatably, wherein the threaded spindle ( 14 ) in sections by a cantilever ( 20 ) surrounded by a first end ( 21 ) in the direction of the longitudinal axis ( 11 ) out of the housing ( 12 protruding at the opposite second end ( 22 ) with a mother ( 30 ), which in the threaded spindle ( 14 ), whereby the nut ( 30 ) with respect to the longitudinal axis ( 11 ) relative to the housing ( 12 ) with an anti-twist device ( 15 ) is secured against twisting, whereby at the first end ( 21 ) of the jib ( 20 ) a ball joint head ( 50 ) with a bearing bore ( 51 ), wherein the electric cylinder ( 10 ) a force sensor ( 60 ), characterized in that the force sensor ( 60 ) from a separate bolt ( 40 ) is formed, which the bearing bore ( 51 ) of the ball joint head ( 50 ) interspersed. Electric cylinder according to claim 1, characterized in that the nut ( 30 ) an internal profiling ( 31 ), wherein a plurality of separate planetary rollers ( 31 ) with an external profiling ( 32 ) provided in both the internal profiling ( 31 ) mother ( 30 ) as well as in the threaded spindle ( 14 ) intervene. Electric cylinder according to one of the preceding claims, characterized in that a first and a second fork leg ( 52 ; 53 ) are provided, between which the ball joint head ( 50 ) is arranged, wherein the bolt ( 40 ) also the first and second fork legs ( 52 ; 53 ) interspersed. Electric cylinder according to one of the preceding claims, characterized in that the bolt ( 40 ) comprises a transformer having at least one primary and at least one secondary coil, which are penetrated by a common ring core, wherein the toroidal core is connected to the bolt so that it is elastically deformed when one in the direction of the longitudinal axis ( 11 ) acting force on the bolt ( 40 ) acts. Electric cylinder according to one of claims 1 to 4, characterized in that the bolt ( 40 ) with at least one ohmic resistance element ( 61 ) provided in such a way with the bolt ( 40 ) is elastically deformed when one in the direction of the longitudinal axis ( 11 ) acting force on the bolt ( 40 ) acts. Electric cylinder according to claim 5, characterized in that the bolt ( 40 ) a first, a second and a third section ( 41 ; 42 ; 43 ), the third section ( 43 ) the bearing bore ( 51 ), the third section ( 43 ) via at least one first bending beam ( 44 ) with the first section ( 41 ), wherein it has at least one second bending beam ( 45 ) with the second section ( 42 ), wherein the first and the second bending beam ( 44 ; 45 ) have a lower flexural rigidity than the first, second and third sections ( 41 ; 42 ; 53 ), wherein the at least one resistance element ( 61 ) with the at least one first and / or with the at least one second bending beam ( 44 ; 45 ) is firmly connected. Electric cylinder according to claim 6, when dependent on claim 3, characterized in that the first section ( 41 ) the first fork leg ( 52 ), the second section ( 42 ) the second fork leg ( 53 ) interspersed. Electric cylinder according to one of the preceding claims, characterized in that the bearing bore ( 51 ) is circular cylindrical, being perpendicular to the longitudinal axis ( 11 ), wherein preferably the first, the second and the third section ( 41 ; 42 ; 43 ) are also formed circular cylindrical. Electric cylinder according to one of the preceding claims, characterized in that the anti-twist device ( 15 ) at one end of the housing ( 12 ) is arranged on which the boom ( 20 ) out of the housing ( 12 ) emerges. Electric cylinder according to one of the preceding claims, characterized in that the bolt ( 40 ) a groove ( 46 ) with a bottom surface ( 47 ), which transversely to the bolt ( 40 ), wherein at least one separate plate ( 70 ) provided in the groove ( 46 ), wherein they have a flat edge surface ( 71 ) at the bottom surface ( 47 ) is present. Electric cylinder according to claim 10, appended to claim 3, characterized in that the at least one plate ( 70 ) on the first / or the second fork leg ( 52 ; 53 ) is fastened and preferably screwed to it.

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