Does anyone know of a good solution for measuring axial force in trapezoidal screw jack, like this: https://en.zimm.com/product-catalogue/screw-jack-ze-series/ze-r-trapezoidal-screw/ ?

Force magnitude is around 50 kN.

I can't measure with torque data from the electric motor, because the screw jack is set and then and then we don't need the motor anymore until the next setting.

I was thinking of a compression load cell under the housing of a screw jack, but I need something that also supports some side forces and most of the load cells need force that is perpendicular. I will also get some side forces, because the screw jack is mounted so that it moves horizontaly.

Any good recommendations and proposals will be useful.

EDIT: Added application sketch. 1

  • $\begingroup$ I might consider a cage that houses a load cell. Fixed rods around the periphery and guides that allow it to telescope against the load cell to minimize side load. Make it all so side loads are minimized and lock down the lift before lifting. If motion is expected during lift, is it possible to make other supports compliant? $\endgroup$
    – Jim Clark
    May 31 at 23:11
  • $\begingroup$ Another thought is to build a rod of suitable material. Place 4-(or more even numbered) strain gages axially and equally spaced around the outside. Averaging (opposite or) all measurements will likely cancel out bending and represent axial load. $\endgroup$
    – Jim Clark
    May 31 at 23:20
  • $\begingroup$ Hey @JimClark, strain gages are not an option, because it is a application for production line, where we would like to use as standard components as possible. I was also thinking about a cage around the sensor, so that we get only axial force on the sensor, other side forces are transfered through the cage. What do you mean with making other supports compliant? I've added a quick sketch of my application. It is a tilting plate mounted in a way that the plate axis is horizontal. With three screw jacks I can adjust plate tilt, but for no more than 3°. $\endgroup$
    – Grega
    Jun 1 at 9:26
  • $\begingroup$ Straing gages are standard components but i belive you can get trapezoidal screws that are alkready instrumented. But why not put the loadcell on the nut itself? On the otherhand you could put it all mounted on a hydraulic bottle and measure there. $\endgroup$
    – joojaa
    Jun 1 at 13:58
  • $\begingroup$ You say you were thinking about a load-cell, but then reject someone's suggestion of a strain gauge. They're the same thing, just the load-cell is a strain-gauge that has been packaged in a mechanical housing. $\endgroup$
    – DKNguyen
    Jun 1 at 18:45

(Other supports compliant) I thought, that if you had an assembly and were straightening out a cantilever portion, you could fix the jack screw and make the other supports compliant. Such as supporting them on bases that have many holes drilled in the bottom and feed shop air into them so they could "fly" and move to accommodate the flexure rather than having the jackscrew be significantly sideloaded.

The image below is a quick cross-section of one concept that might help the active jackscrew allow limited sideload without causing problems.

Ahem, oh well so much for morning drafting, the sleeve bearing on the left should look like the sleeve bearing on the right (you get the idea).

load cell cage and compliant jackscrew support

I've used this mechanism before. The ball provides pivot to the assembly above thus acting as a truss member, that is, acting only in tension or compression.

Alternatively, instead of springs, you could have supports that come up from below to level the system, then after light contact is made, then remove them so the system can pivot freely on the ball (maybe even with springs on top of the supports, etc.).

  • $\begingroup$ Nice solution and great input @Jim Clark. In the meantime we found compression load cell, that is capable of withstanding 100% of compression load also in side directions. pavonesistemi.com/load-cells-universal-cvf, it doesn't say so in the technical specification, but I contacted the manufcturer and this was their information. I will probably design something around this, since we can remove most of the structure, that supports side loads. I only have to check for moment loads. $\endgroup$
    – Grega
    Jun 2 at 7:36
  • $\begingroup$ Did you draw the sleeve bearings on the left in the wrong place and give up? $\endgroup$
    – DKNguyen
    Jun 2 at 14:08
  • $\begingroup$ I drew the rolling spheres in the wrong place, took a photo with my phone, transferred it to the computer, included it in the post, and found it was poorly drawn. I was leaving for work in 10-minutes, and instead of repeating the process, I wrote my comments, submitted it, and departed. It's just a concept to be built upon/improved. $\endgroup$
    – Jim Clark
    Jun 2 at 14:30
  • $\begingroup$ Hi everyone. Just to inform a little bit. I designed the system and it will go into detailing soon. I will post back here when everything is finished, to put some additional value in this post... $\endgroup$
    – Grega
    Jul 13 at 6:54

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