I used a resource from a book on the exploitation of constructions by graphic statics. So far so good, digging into the possibilities I have made a modalization of a double scissor lift table............... by setting the formula to obtain the effective load of the cylinder according to its anchor points, Solidworks performs the calculation but if we put the calculation by hand........ The value is different............ 6666 daN instead of 7850.27 daN.
Can someone clarify the error that was made during the processing of this information.
You are in version 2020 or higher, so I can't open your file which is also a part file and not an ASM file.
Post pictures of the parameters used for the simulation and also very importantly the pictures of the part with the places where you put the connectors.
Kind regards
PS: did you have a solid training on the simulation module?
In fact it's an approach and for the moment I only use a 2D sketch as a reference, then a copy of this sketch by applying a small variation in the height to obtain the load of the cylinder. The method is described step by step, it is the calculation by solidworks which is different from a manual calculation, not a drift problem.......... I don't understand.
Thank you for your answer, I will do a complete study with an assembly as soon as this step is consolidated.
I don't understand your reasoning, I don't see what the problem is.
Summarize:
As long as your two members are of the same length and the central axis is located at 500 mm for the two members and the two low points (axes) are as on the constrained sketch on the horizontal construction line (here connected to the origin), you must have a symmetry. After that, it is the variable length of the cylinder that makes the upper plate rise or fall (and not the rating of 300 unless you put a horizontal cylinder.
You say (set a range of operation of the table.) In fact, it is the effort required to start the climb when the table top is totally in the starting position at the very bottom. The maximum effort is at this beginning of the cycle and if you go too low it will be blocked. After the other criterion for the high point of the table is the position of the theoretical CG because if you raise your table too high will risk tipping over.
As an example, for a current starting height of 200 mm, the force on the cylinder will be about 19521 N for a load of 100 kg and a mass with a centered CG. Note that the maximum force will be in X on the bar of the first junction (axis with the second scissors) and will be 29282 N at start-up. This junction will always be the most stressed compared to the other axes, regardless of the height.
The error is only apparent... Your calculation with Excel uses values rounded to two decimal places for the cylinder lengths. As the movements are very small, these roundings have a significant, even enormous, effect on your calculation. Switch to 4 decimal places as for the dimensions displayed in your sketch, and you will have a consistent result: 7843 N. Compare this to the value of 7850 N given by SolidWorks.
SolidWorks probably uses a significant number of decimal places... Note that SolidWorks declares a circular reference problem of the dimensions in the equations folder, which does not seem to me to be the case.
What is the rating of 300 that you mentioned in your last message?
A recommendation: use the equal-dimensional properties of the bars and other geometric elements between your two graphs, so that a change in one is immediately reflected in the other. Hence the presence of the construction circles for the dimensions 350 and 530 mm. And a significant lightening of the scheme...
you say (by varying the center of gravity of the load, the force in the cylinder remains a constant.), it's true, but obviously the forces in the bars will change at the level of the axes (but that's another story ;-) )
Second question, which I discovered just now, and relating, if I understand correctly, to the position of the axis of symmetry of the "chisel", which you want to freeze... The left foot of your chisel is stationary, since it coincides with the origin of the sketch. All we have to do is remove this coincidence relationship and define the dimension of 300 mm between the origin and the vertical construction line passing through the "joint" of the chisel. The diagram still has a degree of mobility, but moving a foot will no longer change the position of the axis of symmetry... If you remove the "driven" property from the corner dimension, the sketch is fully constrained.
Thank you very much m.blt for the help and the explanations, I understand the problem comes from the exploitation of decimals, it's a trap.
I find that this approach is easy to have the load on a mechanism with a cylinder, I also share the Zozo complement, it will change the forces in the connections and there a simulation becomes relevant otherwise we can do several dynamics by isolating the elements one by one (bring back to 3 forces + balance).
