LOAD SIMULATION TEST STAND AND METHOD OF OPERATING SAME

Abstract

The invention relates to a load simulation test stand having at least one hydraulic test cylinder (1) which comprises at least one cylinder chamber (1a, 1b) which can be charged with hydraulic fluid, preferably two cylinder chambers (1a, 1b) which can be charged with hydraulic fluid and which act counter to one another, in the case of which load simulation test stand the at least one test cylinder (1), in particular each of multiple provided test cylinders (1), comprises at least one capacity element (5, 6, 7), preferably a capacity element (5, 6, 7) which is exchangeable or which is adjustable in terms of hydraulic capacity, by means of which the hydraulic overall capacity of the at least one cylinder chamber (1a, 1b) can be adjusted. The invention furthermore relates to a method for operating a load simulation test stand having at least one test cylinder (1), wherein the at least one test cylinder (1) is connected to a load which is to be moved, and wherein the load is moved by means of a pressure control system (4) by temporally changeable control of the fluid pressure in the at least one cylinder chamber (1a, 1b) of the at least one test cylinder (1), and wherein, for the load which is to be moved by means of the at least one test cylinder (1), in a manner dependent on the pressure control bandwidth of the pressure control system (4), the natural frequency of the unit composed of the at least one test cylinder (1) and load is set to a value smaller than the pressure control bandwidth by changing the capacity of the capacity element (5, 6, 7), preferably adjusting the capacity of the adjustable capacity element (5, 6, 7).

Claims

1. A load simulation test stand comprising a hydraulic test cylinder having two hydraulic fluid compartments that can be acted upon with hydraulic fluid and that work against one another, wherein the test cylinder comprises a capacity element that is exchangeable or adjustable with respect to hydraulic capacity and with which the total hydraulic capacity of the compartment is adjustable.

2. The load simulation test stand according to claim 1, wherein the test cylinder has for each of its compartments a separate adjustable capacity element.

3. The load simulation test after claim 1, wherein the capacity element is external to the respective test cylinder and in direct fluidic connection to the compartment.

4. The load simulation test stand according to claim 3, characterized that the external capacity element of the test cylinder is formed as: a membrane expansion tank having a membrane with one side acted on by the hydraulic fluid of the compartment and an opposite side movable by a gas, whose pressure can be adjusted to change the capacity value, or an expansion hose assembly, preferably whose effective total hose length is adjustable, or a resilient assembly made of an elastomeric and fluid-filled body, the fluid pressure in the cavity of the body is adjustable.

5. The load simulation test according to claim 1, wherein the capacity element, preferably each of the capacity elements, is in the compartment of the test cylinder and is acted on by the hydraulic fluid of the compartment.

6. The load simulation test stand according to claim 5, wherein the internal capacity element of the test cylinder is formed as: a elastomeric hollow fluid-filled body in which fluid pressure in a cavity of the body is adjustable, or a membrane expansion tank whose the membrane has one to side acted upon by the hydraulic fluid of the compartment and an opposite other side acted upon by a gas, whose pressure is adjustable to change the capacity value.

7. A method of operating a load simulation test stand comprising a test cylinder according to one of the previous claims, wherein the test cylinder is connected to the load to be moved and a pressure-control system with a time-changeable control of the fluid pressure in the compartment of the test cylinder moves the load, wherein for the load being moved by the test cylinder depending on the load pressure-control bandwidth of the pressure-control system, the resonant frequency of the assembly of the test cylinder and load is set by setting the capacity of the adjustable-capacity element to a value smaller than the pressure-control bandwidth.

8. The method according to claim 7, wherein the resonant frequency is set to a value of 30% to 70%, of the pressure-control bandwidth.

9. The method according to one of the preceding claim 7, wherein target fluid pressure set points of the pressure-control system in dependence on a given target movement of the load are determined directly in real time without the target fluid pressure set points being previously determined by metrological detection of the movement of the load to approach the specified target movement with iteration.

Description

[0041] The invention is explained in more detail with reference to the attached figures in which:

[0042] FIG. 1 shows an overall schematic view of a load simulation test stand that here, in particular for the sake of simplicity, has only one test cylinder 1. In actual practice it is however preferable to provide the load simulation test stand to operate with several such test cylinders 1, for example with several actuators for moving a load 2, including several test cylinders, as for example is the case with a hydraulic hexapod. In this example, the test cylinder 1 is a synchronized cylinder whose compartments 1a and 1b are controlled by a valve 3 of a pressure-control system 4 operated hydraulically by a hydraulic system 4a of the pressure-control system. A differential cylinder, for example, can also be used.

[0043] FIG. 1 shows that the load 2 here is attached via an adapter on the piston rod of the synchronizing cylinder, forming a jointly moving mass that is the sum of the masses of the piston rod, piston, adapter and the load 2 attached to it.

[0044] According to the invention, there is a respective external capacity element 5 for variably adjusting entire hydraulic capacity of each of the two compartments 1a and 1b. In this example the hydraulic capacity element 5 is a membrane expansion vessel where a face of the membrane turned away from the face subjected to the hydraulic fluid is pressurized via a line 5a. The membrane thus separates two compartments that, except for the membrane, are delimited by rigid walls. The ability to adjust the fluid pressure eliminates the need to change the capacity value of the membrane expansion tank against with another with a different capacity, which the invention, however, also includes.

[0045] According to FIG. 2, the invention can also provide as alternative to the capacity element 5 of FIG. 1 a capacity element 6 that is structurally formed as an expansion tube, preferably as an assembly of at least two expansion hoses can be connected together by valves 6a optionally so that the effective total length of the stretchable hose can be optionally set.

[0046] As a further alternative, according to FIG. 3 one of the compartments is for example provided with an elastomeric end stop 7 in direct fluid contact with the fluid are inside the compartment and preferably filled with a fluid, preferably a gas in a cavity whose the pressure of which can be changed via the line 7a.

[0047] FIGS. 1 to 3 each show essentially the same overall system, with only the capacity elements 5, 6, 7 different in type and preferably in each case in adjustable capacity. Instead of the alternative use these capacity elements can also be used cumulatively. And several different species capacity elements per compartment are possible.

[0048] For all possibilities of the realizable, preferred adjustable capacity elements, they are permanently connected to the respective compartments 1a and 1b and/or with the fluid of the respective compartment 1a, 1b. Consequently it is essential for the invention that a respective, preferably a capacity element that is adjustable in terms of the capacity is not separated from the cylinder by the valve 3 that is part of in pressure-control system for the application to the compartments of pressure which can be changed over time.

[0049] The pressure-control system here includes a reversible valve 3, with which the hydraulic fluid is supplied under pressure by a pump 4b from a tank 4c, and, depending on position, is fed into one of the two compartments 1a or 1b and at the same time is returned from the other compartment to the tank 4c.

[0050] The valve is controlled by control electronics 4d using pressure sensors to record the pressure P1 or P2 in the compartments 1a and 1b and compare these pressure as actual values with the target value and from this control the valve 3.

[0051] This described pressure control described can be part of an overriding further control that is not shown here and that regulates another variable, for example the movement or the position or speed of the load.

[0052] By changing the hydraulic capacity of the respective capacity element 5, 6 or 7 by exchanging the capacity elements against those of other capacities or by adjusting its own capacity, the resonant frequency of the entire assembly of the test cylinder and its load 2 for each cylinder chamber 1a, 1b is set to a value smaller than the control bandwidth of the pressure-control system 4, in particular as required by the system.

[0053] For example, the pressure-control bandwidth can be a system constant determined by the elements of the pressure-control system. In recognition of this pressure-control bandwidth and, in particular, therefore the upper limit frequency that this pressure-control system can reach, the resonant frequency of the assembly of the load and the load test cylinder can now be determined are selected so that the resonant frequency is smaller than the upper frequency limit and preferably in the range from 30% to 70%, more preferably 40% to 60% and particularly preferably 45% to 55% of the pressure-control bandwidth or the upper frequency limit.