Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L3/00—Measuring torque, work, mechanical power, or mechanical efficiency, in general
  • G01L3/02—Rotary-transmission dynamometers
  • G01L3/04—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft
  • G01L3/10—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating
  • G01L3/106—Rotary-transmission dynamometers wherein the torque-transmitting element comprises a torsionally-flexible shaft involving electric or magnetic means for indicating involving electrostatic means

Definitions

• the invention relates to a housing for a sensor for measuring changes in length or distance, in particular for a torque sensor with a capacitive converter.
• a measuring sensor for changes in length or distance is known, which is particularly suitable for the contactless measurement of torques on rotating shafts.
• a capacitor arrangement with two electrode structures which can be adjusted in parallel is provided as the adjustable capacitance.
• the interdigitated electrode structures which are preferably comb-shaped, each consist of a plurality of planar electrodes arranged parallel to one another, which are assigned to one another in pairs.
• a highly asymmetrical arrangement of the electrode structures achieves capacitive decoupling, so that the total capacitance of the capacitor arrangement results from a parallel connection of electrode pairs, which are each formed by electrodes which are assigned to one another.
• the change in capacitance caused by the variable electrode spacing of the electrode pairs serves as the measured variable.
• electrode structures designed as microstructures for example, torsions of a few micrometers can be detected.
• the actual sensor element essentially consists of the functional groups comb structure and the necessary elastic and hermetic encapsulation.
• the need for hermetic encapsulation results from the capacitive sensor principle.
• the elasticity is determined by the transfer of the elongation to be measured, ie a change in length or also by the transfer of an extension. Change in position to the electrode spacing of the capacitor arrangement is required.
• high demands are to be placed on the fatigue strength with respect to vibrations.
• the transmission of the change in length or distance through the housing to the capacitor arrangement must be designed in such a way that only displacements in the measuring direction have an influence on the measurement result.
• Thermal expansions of the measurement object and expansions of the second order which are caused, for example, by transverse forces, bending moments or axial forces, must not cause any additional change in the electrode spacing.
• the double-comb structure of the capacitor arrangement is fastened in isolation in a metallic housing frame, which converts the displacement to be measured as a parallelogram guide into a corresponding change in the distance between the electrode pairs.
• the housing frame is designed with corresponding weak points.
• the hermetic encapsulation of the capacitor arrangement can then take place by covering the housing frame with metallic foils on both sides, the housing frame and foils being connected by resistance welding, preferably by roller seam welding.
• the parallelogram arrangement ensures that the capacitor electrodes are guided exactly to one another, but the corners of the welded cover foils occur considerable voltages, which can lead to problems in the case of continuous load changes in the order of magnitude of, for example, 10 10 . It can also hermetically seal the weld at the weak points in the corner areas of the housing frame when there is a permanent load change.
• the invention has for its object to provide a housing for a sensor for measuring changes in length or distance, in which the requirements for permanent tightness, elastic deformability and high fatigue strength are met at the same time.
• a generic housing with a sensor guide arranged inside the housing that only allows movement in the measuring direction, at least elastically deformable in the measuring direction, mechanically largely decoupled from the sensor guide and continuously running in the circumferential direction, and with two cylinder segments the housing interior tightly sealing, at least elastically deformable in the measuring direction housing covers.
• housings designed according to the invention are suitable for accommodating the capacitive torque sensors described at the outset, but also for other sensors for measuring changes in length or distance. Conventional strain gauges can be mentioned here as an example. Preferred embodiments of the invention are specified in the subclaims.
• Figure 1 and Figure 2 in plan view and in side view of a housing for a torque sensor with a capacitive converter without the associated housing covers.
• Figure 3 shows a housing according to Figures 1 and 2, but with the associated housing covers in perspective Dar position and
• Figure 4 shows a housing according to Figures 1 and 2 without housing covers and without torque sensor in perspective.
• FIGS. 1 and 2 show a top view and a side view of a housing for a capacitive torque sensor denoted by DS, the structure and mode of operation of which can be found in EP-B-0 354 386.
• DS capacitive torque sensor
• the housing fuselage shown which consists for example of steel, is produced in one piece, for example by injection molding, by laser cutting or by wire EDM.
• the one-piece housing body comprises a sensor guide SF designed as a parallelogram guide with two transverse webs QS and four elastically deformable joints GE, two mutually opposite external fastening parts BT, each connected to the sensor guide SF via a leaf spring BF, and a circular cylindrical housing jacket GM two opposite, elastically deformable circular cylinder segments ZS.
• the fastening parts BT each provided with two fastening holes BL, are fastened in the circumferential region of a shaft by means of corresponding fastening screws (not shown in the drawing), a torsion of the shaft indicated by arrows PF being transmitted to the sensor guide SF as a change in length.
• the attachment via the fastening parts BT can, however, also be carried out in a radial alignment in the end region of a shaft or an elastic transmission member.
• the torsion measured by the strain sensor DS represents a measure of the transmitted torque. It is important that the sensor guide SF only allows movement in the measuring direction MR running parallel to the arrows PF.
• FIG 1 the course of a weld SN is indicated by a circular, dash-dotted line, with which two corresponding housing covers are to be connected to the housing jacket GM.
• FIG 3 the upper of these two housing covers designated GA can be seen.
• the housing covers GA are structured by a concentric, circular undulation W. This structuring W in the form of several concentric, bead-like grooves semicircular in cross section results in a slight elastic deformability of the housing covers GA, i.e. the housing covers GA can easily undergo elastic deformations of the circular cylinder segments ZS.
• the hermetically sealed connection of the housing covers GA, which is designed as a steel foil, to the housing body is preferably carried out by roller seam welding, the circular course of the weld seam SN, as already mentioned in FIG. 1, being indicated by a dash-dotted line.
• FIG. 4 shows the open housing body without the torque sensor DF shown in FIG. 1. It can be seen that the sensor guide SF two parallel to the crossbars QS and Has extensions FO oriented perpendicular to the measuring direction MR. The torque sensor DS is attached to these two extensions FO in the position shown in FIG. 1, for example by soldering.
• the housing covers GA required for hermetic encapsulation are circular, so that the roll seam welding can be carried out on arcs of constant width, this width being, however, significantly larger than the weak points forming the joints GE the cross bars QS of the sensor guide SF.
• the circular arc shape ensures easy deformability and a more even distribution of stress.
• the parallel movement of the electrodes of the torque sensor DS is ensured, as already mentioned, by the sensor guide SF designed as a parallelogram with the four joints GE.
• the structure of the housing covers GA explained above results in an extremely easy deformability of these covers.
• FIGS. 1 to 4 Further advantages of the housing shown in FIGS. 1 to 4 result from the one-piece connection of the fastening parts BT to the housing body via the leaf springs BF, which are likewise formed by weak points.
• These leaf springs BF mechanically decouple temperature-related expansions or expansions of the second order, as well as the shape and position tolerances of the fastening surfaces or the measurement object.
• the number of degrees of freedom of this mechanical decoupling depends on the fastening method chosen. This ensures that only the change in elongation or length in the measuring direction is transmitted exactly to the measuring capacitor of the torque sensor DS and that no additional voltages are introduced into the area of the elastic encapsulation.
• the proposed design of a hermetic-elastic encapsulation for a capacitive tive torque sensor or strain sensor the following decisive improvements: significantly less stress on the material and the roller seam welding, thereby significantly improved fatigue strength, much better durability of the hermetic encapsulation,

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=7815051

Family Applications (1)

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Family Cites Families (5)

• 1997
  • 1997-11-10 JP JP10527164A patent/JP2000507711A/ja active Pending
  • 1997-11-10 EP EP97949905A patent/EP0948738A1/de not_active Withdrawn
  • 1997-11-10 WO PCT/DE1997/002627 patent/WO1998027410A1/de not_active Application Discontinuation

Non-Patent Citations (1)

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