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US-12627209-B2 - Constant force generator

US12627209B2US 12627209 B2US12627209 B2US 12627209B2US-12627209-B2

Abstract

A constant force generator comprises a stator having a longitudinal axis and a permanently magnetic stator region, and an armature arranged to be movable relative to the stator in the direction of the longitudinal axis, the armature having a permanently magnetic armature region. The permanently magnetic stator region and the permanently magnetic armature region are each magnetized in a magnetization direction perpendicular to the direction of the longitudinal axis. The permanently magnetic armature region has a first sub-region which has a magnetization having a net magnetization component in a direction opposite to the magnetization direction of the permanently magnetic stator region, so that in the case of an only partly overlapping arrangement of the first sub-region and the permanently magnetic stator region, the net force component has a repulsive net force component which repels the armature away from the stator in the direction of the longitudinal axis.

Inventors

  • Ronald Rohner
  • Daniel Ausderau

Assignees

  • NTI AG

Dates

Publication Date
20260512
Application Date
20230703
Priority Date
20220706

Claims (15)

  1. 1 . A constant force generator, especially a tubular constant force generator, comprising: a stator which has a longitudinal axis and a permanently magnetic stator region, wherein the permanently magnetic stator region has a first longitudinal end and a second longitudinal end which is located axially opposite the first longitudinal end, and an armature which is arranged so as to be movable relative to the stator over a stroke in the direction of the longitudinal axis, which armature has a permanently magnetic armature region, wherein the permanently magnetic stator region and at least in part also the permanently magnetic armature region are each magnetized in a magnetization direction perpendicular to the direction of the longitudinal axis, and wherein the permanently magnetic stator region and the permanently magnetic armature region are arranged so as to be only partly overlapping in the direction of the longitudinal axis over the entire stroke of the armature, so that a magnetic force acting between the permanently magnetic stator region and the permanently magnetic armature region has a net force component in the direction of the longitudinal axis that is constant over the entire stroke, and wherein the permanently magnetic armature region has a first sub-region which has a magnetization having a net magnetization component in a direction opposite to the magnetization direction of the permanently magnetic stator region, so that in the case of an only partly overlapping arrangement of the first sub-region and the permanently magnetic stator region such that a longitudinal portion of the first sub-region protrudes from the permanently magnetic stator region in the direction of the longitudinal axis solely at the first longitudinal end of the permanently magnetic stator region, the net force component which is constant over the entire stroke comprises a repulsive constant net force component which repels the armature away from the first longitudinal end of the stator in the direction of the longitudinal axis.
  2. 2 . The constant force generator according to claim 1 , wherein the direction of the magnetization of the first sub-region of the permanently magnetic armature region is opposite to the magnetization direction of the permanently magnetic stator region.
  3. 3 . The constant force generator according to claim 1 , wherein the direction of the magnetization of the first sub-region of the permanently magnetic armature region and the magnetization direction of the permanently magnetic stator region enclose an obtuse angle.
  4. 4 . The constant force generator according to claim 1 , wherein the strength of the magnetization of the permanently magnetic stator region, viewed in the direction of the longitudinal axis, is constant over the length of the permanently magnetic stator region in order to generate a magnetic field which, viewed in the direction of the longitudinal axis, is homogeneous over the length of the permanently magnetic stator region and declines away from the first longitudinal end and from the second longitudinal end of the permanently magnetic stator region, viewed along the longitudinal axis, and wherein the strength of the magnetization of the first sub-region of the permanently magnetic armature region, viewed in the direction of the longitudinal axis, is constant over the length of the first sub-region of the permanently magnetic armature region.
  5. 5 . The constant force generator according to claim 1 , wherein the permanently magnetic armature region has a second sub-region which either is permanently magnetic and has a magnetization having a net magnetization component in a direction identical with the magnetization direction of the permanently magnetic stator region, or which consists of a magnetically conductive material, so that in the case of an only partly overlapping arrangement of the second sub-region and the permanently magnetic stator region such that a longitudinal portion of the second sub-region protrudes from the permanently magnetic stator region in the direction of the longitudinal axis solely at the second longitudinal end of the permanently magnetic stator region, the net force component which is constant over the entire stroke comprises an attractive constant net force component which attracts the armature towards the second longitudinal end of the stator in the direction of the longitudinal axis, the attractive and repulsive constant net force components pointing in the same direction, wherein in the case of the only partly overlapping arrangement of the first sub-region and the permanently magnetic stator region such that a longitudinal portion of the first sub-region protrudes from the permanently magnetic stator region in the direction of the longitudinal axis solely at the first longitudinal end of the permanently magnetic stator region, the repulsive constant net force component acts on the protruding longitudinal portion of the first sub-region, and wherein in the case of the only partly overlapping arrangement of the second sub-region and the permanently magnetic stator region such that a longitudinal portion of the second sub-region protrudes from the permanently magnetic stator region in the direction of the longitudinal axis solely at the second longitudinal end of the permanently magnetic stator region, the attractive constant net force component acts on the protruding longitudinal portion of the second sub-region.
  6. 6 . The constant force generator according to claim 5 , wherein in the case where the second sub-region of the permanently magnetic armature region is permanently magnetic, the strength of the magnetization of the second sub-region is constant over its length in relation to the direction of the longitudinal axis, and in the case where the second sub-region of the permanently magnetic armature region is magnetically conductive, the magnetic conductivity of the second sub-region is constant over its length, viewed in the direction of the longitudinal axis.
  7. 7 . The constant force generator according to claim 5 , wherein the first sub-region and the second sub-region of the permanently magnetic armature region are arranged spaced apart from one another in the direction of the longitudinal axis by a distance that is smaller than 90% of the length of the permanently magnetic stator region.
  8. 8 . The constant force generator according to claim 5 , wherein the first sub-region and the second sub-region of the permanently magnetic armature region are arranged spaced apart from one another in the direction of the longitudinal axis by a distance that is substantially the same as the length of the permanently magnetic stator region.
  9. 9 . The constant force generator according to claim 5 , wherein the first sub-region and the second sub-region of the permanently magnetic armature region are both permanently magnetic, and wherein the strength of the magnetization of the second sub-region of the permanently magnetic armature region is reduced by from 10% to 40% relative to the strength of the magnetization of the first sub-region of the permanently magnetic armature region.
  10. 10 . The constant force generator according to claim 1 , wherein the constant force generator comprises a further stator having a further stator region which either is permanently magnetic and has a magnetization having a net magnetization component in the direction of the magnetization of the first sub-region of the permanently magnetic armature region, or which consists of a magnetically conductive material, wherein the further stator region has a further first longitudinal end as well as a further second longitudinal end which is located axially opposite the further first longitudinal end, and wherein the further second longitudinal end of the further stator region faces towards the first longitudinal end of the permanently magnetic stator region, wherein the first sub-region of the permanently magnetic armature region and the further stator region are arranged so as to be only partly overlapping in the direction of the longitudinal axis in such a way that a further longitudinal portion of the first sub-region protrudes from the further permanently magnetic stator region in the direction of the longitudinal axis solely at the further second longitudinal end of the further permanently magnetic stator region, so that a magnetic force acting between the first sub-region and the further stator region has a further constant net force component in the direction of the longitudinal axis which attracts the armature towards the further stator in the direction of the longitudinal axis, that further constant net force component pointing in the same direction as the repulsive constant net force component.
  11. 11 . The constant force generator according to claim 10 , wherein in the case where the further stator region is permanently magnetic, the strength of the magnetization of the permanently magnetic further stator region is constant over its length, viewed in the direction of the longitudinal axis, in order to generate a magnetic field which, viewed in the direction of the longitudinal axis, is homogeneous over the length of the further permanently magnetic stator region and declines away from the further first longitudinal end and from the further second longitudinal end of the further permanently magnetic stator region, viewed along the longitudinal axis, and in the case where the further stator region is magnetically conductive, the magnetic conductivity of the magnetically conductive further stator region is constant over its length, viewed in the direction of the longitudinal axis.
  12. 12 . The constant force generator according to claim 1 , wherein the constant force generator, especially the tubular constant force generator, comprises a securing device against rotation of the armature relative to the stator about the longitudinal axis.
  13. 13 . A linear drive system having a linear motor, especially a tubular linear motor, which comprises a motor stator having a drive longitudinal axis, and a motor armature which is movable relative to the motor stator in the direction of the drive longitudinal axis, wherein the linear drive system further comprises a constant force generator according to claim 1 .
  14. 14 . The linear drive system according to claim 13 , wherein the motor armature is axially fixedly connected to the armature of the constant force generator.
  15. 15 . The linear drive system according to claim 13 , wherein the linear drive system comprises at least two constant force generators wherein armatures of the at least two constant force generators are axially fixedly connected to one another and axially fixedly connected to the motor armature.

Description

REFERENCE TO RELATED APPLICATION This application claims the benefit of priority to European Patent Application No. 22183245.4, filed on Jul. 6, 2022, which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application. The present invention relates to a constant force generator according to claim 1 and to a linear drive system according to claim 13. Linear drive systems are used for moving masses along a (typically) straight travel path. If the straight travel path runs solely in a horizontal direction, the force applied by the linear drive system typically needs only to counteract the inertia of the mass and frictional forces. If, however, the straight travel path runs in a vertical direction or at least has a gradient, the linear drive system needs to apply an additional force in order to counteract the weight force acting on the mass, even when the mass is at rest. In the case of an electromagnetically operated linear drive system, its linear motor must in that case be continuously energised in order to counteract the weight force acting on a mass coupled to the linear drive system and accordingly in order to keep the mass at rest. The continuous energisation of the linear motor subjects the linear motor to additional strain and the linear motor suffers losses (for example due to heat). The (constant) force required which serves only to counteract the weight force can be disproportionately large in relation to the force required for moving the mass. In order that the linear motor of the linear drive system does not have to be specially designed merely in order to be able to apply the additional constant force for counteracting the weight force, there are various solutions by which a force that counteracts the weight force can be generated by means of an additional device. Such solutions include force-generating elements such as counterweights and mechanical springs as well as pneumatic systems. A further solution is a constant force generator, in which the weight force is compensated by a magnetic attraction force between permanently magnetic regions that are magnetized in the same direction or between a permanently magnetic region and a magnetically conductive region (for example a ferromagnetic region) having a net force component opposite to the weight force. Such a passive constant force generator has the advantage of neither requiring the application of electrical power in order to compensate the effect of the weight force nor giving rise to high mechanical stresses leading to excess wear. Another application of a constant force generator is, for example, a process in which the motor needs to apply a constant force, for example for pressing against a closing spring, which force is applied by the constant force generator instead of by the motor. Moreover, a constant force generator mechanically coupled to the motor can be advantageous in that, in the event of a loss of power, the armature can be moved automatically into a desired end position (for example into a safe position) by the magnetic force of the constant force generator. Depending upon the configuration of the constant force generator and the manner of its coupling to the motor, in the event of a lack of power a pushing constant force is able to move the armature forwards or a pulling constant force is able to retract the armature. EP 1 378 986 A1 describes such a constant force generator. In that constant force generator a armature of the constant force generator is guided in a stator of the constant force generator, both the armature and the stator each having a permanently magnetic region or at least a magnetically conductive region. As a result of a magnetic attraction force acting between the permanently magnetic or magnetically conductive regions of the armature and the stator, the armature is attracted in the direction of the stator. The permanently magnetic or magnetically conductive region of the stator is designed in such a way that the resulting magnetic field is inhomogeneous only in a region of a longitudinal end of that region of the stator, so that the portion of the armature guided inside the stator is subject only to very small magnetic forces or to no magnetic force. The armature is accordingly drawn into the stator only on a sub-portion of the armature that protrudes from the permanently magnetic or magnetically conductive region of the stator, which sub-region is located in the region of the one longitudinal end of the stator. Consequently, the force which the constant force generator transmits by means of the armature is always directed opposite to the direction in which the armature protrudes from the stator or the magnetic region thereof. This is disadvantageous, especially in respect of the installation space required for applications in which the armature is to provide a pushing constant force. Furthermore, this limits the scope for arrang