LINEAR MEASUREMENT IN PISTON-CYLINDER ARRANGEMENTS

Abstract

The invention relates to a method for measuring the position of a piston-cylinder arrangement, said method comprising: providing the piston-cylinder arrangement, providing an electrical circuit unit, applying a DC voltage (Vcc) to the piston-cylinder arrangement, sensing a capacitance (C) of the piston-cylinder arrangement as an input variable for the electrical circuit unit, generating a pulsed DC voltage (Vcc) by means of the electrical circuit unit on the basis of the sensed capacitance (C) of the piston-cylinder arrangement, providing a measuring unit for measuring a frequency (F.sub.0, F.sub.1) of the pulsed DC voltage (Vcc) generated, determining a frequency difference (DF) between the frequency (F.sub.0) of the pulsed DC voltage (Vcc) before displacement of the piston within the cylinder and the frequency (F.sub.1) of the pulsed DC voltage (Vcc) after displacement of the piston within the cylinder, determining a displacement distance of the piston within the cylinder on the basis of the frequency difference (DF).

Claims

1. A method for measuring the position of a piston-cylinder arrangement, which comprises a cylinder and a piston movable within the cylinder, said method comprising: providing the piston-cylinder arrangement, providing an electrical circuit unit, applying a DC voltage (Vcc) to the piston-cylinder arrangement, sensing a capacitance (C) of the piston-cylinder arrangement as an input variable for the electrical circuit unit, generating a pulsed DC voltage (Vcc) by means of the electrical circuit unit on the basis of the sensed capacitance (C) of the piston-cylinder arrangement, providing a measuring unit used to measure a frequency (F.sub.0, F.sub.1) of the pulsed DC voltage (Vcc) generated, determining a frequency difference between the frequency (F.sub.0) of the pulsed DC voltage (Vcc) before displacement of the piston within the cylinder and the frequency (F.sub.1) of the pulsed DC voltage (Vcc) after displacement of the piston within the cylinder, and determining a displacement distance of the piston within the cylinder on the basis of the frequency difference (DF).

2. The method according to claim 1, wherein a piston rod is connected to the piston in an electrically conductive manner, and wherein the DC voltage (Vcc) is applied to the cylinder and to the piston rod.

3. The method according to, wherein a piston seal and/or piston guide and/or piston rod seal and/or piston rod guide is designed in an electrically insulating manner.

4. The method according to claim 1, wherein an outer tube is arranged on the cylinder and surrounds the cylinder.

5. The method according to claim 1, wherein capacitances (C) to be measured are in the range from 0.5 pF to 50 pF, in particular in the range from 1 pF to 25 pF.

6. The method according to claim 1, wherein the piston-cylinder arrangement is a gas spring or a damper.

7. A device for sensing a change in the extension of a piston-cylinder arrangement, the device comprising: the piston-cylinder arrangement, which comprises a cylinder and a piston that is movable within the cylinder, an electrical circuit unit, which is configured to apply a DC voltage (Vcc) to the piston-cylinder arrangement, and a capacitance determination unit, which is configured to determine a capacitance (C) of the piston-cylinder arrangement, wherein the electrical circuit unit is configured to generate a pulsed DC voltage (Vcc) on the basis of the sensed capacitance (C) of the piston-cylinder arrangement, the device further comprising: a measuring unit, which is configured to measure a frequency (F.sub.0, F.sub.1) of the pulsed direct current (Vcc) generated, and an evaluation unit, which is configured to determine a frequency difference (DF) between the frequency (F.sub.0) of the pulsed direct current (Vcc) before displacement of the piston within the cylinder and the frequency (F.sub.1) of the pulsed direct current (Vcc) after displacement of the piston within the cylinder, and which is further configured to determine a displacement distance of the piston within the cylinder on the basis of the frequency difference (DF).

8. The device according to claim 7, wherein a piston rod is connected to the piston in an electrically conductive manner, and wherein the electrical circuit unit is configured to apply the DC voltage (Vcc) to the cylinder and to the piston rod.

9. The device according to claim 7, wherein a piston seal and/or piston guide and/or piston rod seal and/or piston rod guide is designed in an electrically insulating manner.

10. The device according to claim 7, wherein an outer tube is arranged on the cylinder and surrounds the cylinder.

11. The device according to claim 7, wherein capacitances (C) to be measured are in the range from 0.5 pF to 50 pF.

12. The device according to claim 11, wherein the capacitances (C) to be measured are in the range from 1 pF to 25 pF.

13. The device according to claim 7, wherein the piston-cylinder arrangement is a gas spring or a damper.

Description

[0028] The present invention is described hereinafter with reference to the accompanying drawing, in which:

[0029] FIG. 1 shows an electrical circuit unit that is connected to a piston-cylinder arrangement according to the present invention.

[0030] FIG. 1 illustrates an electrical circuit unit (generally referred to using reference numeral 10) as provided by the device according to the invention. A DC voltage Vcc, which is also applied to the piston-cylinder arrangement 12 that is connected to electrical connection C, is applied to the electrical circuit unit 10. The piston-cylinder arrangement 12 is charged via resistors R.sub.A and R.sub.B and is discharged only via resistor R.sub.B, in which case the discharge voltage of the piston-cylinder arrangement 12 is fed into the input DISCH of the electrical circuit unit 10.

[0031] The following formulas are used to calculate the input voltage at the input DISCH with respect to a frequency F.sub.1 that is emitted at the OUTPUT.

[0032] Calculation of the output high-level duration t.sub.H and the output low-level duration t.sub.L:

t.sub.H=0.693(R.sub.A+R.sub.B)C(1)

t.sub.L=0.693(R.sub.B)C(2)

further:

[00001]$\begin{array}{cc}\mathrm{Period}=t_H+t_L=0.693.Math..Math.\left(R_A+2.Math.R_B\right).Math..Math.C& \left(3\right)\\ \mathrm{Frequency}\frac{1.44}{\left(\mathrm{RA}+2.Math.\mathrm{RB}\right).Math..Math.C}& \left(4\right)\\ \mathrm{OUTPUT}.Math..Math.\mathrm{driver}.Math..Math.\mathrm{working}.Math..Math.\mathrm{cycle}=\frac{t_L}{t_H+t_L}=\frac{R_B}{R_A+2.Math.R_B}& \left(5\right)\\ \mathrm{OUTPUT}.Math..Math.\mathrm{waveform}.Math..Math.\mathrm{working}.Math..Math.\mathrm{cycle}=\frac{t_H}{t_{H+t_L}}=1-\frac{R_B}{R_{A+2.Math.R_B}}& \left(6\right)\\ \mathrm{Low}.Math.\text{-}.Math.\mathrm{to}.Math.\text{-}.Math.\mathrm{high}.Math..Math.\mathrm{ratio}=\frac{t_L}{t_H}=\frac{R_B}{R_A+R_B}& \left(7\right)\end{array}$

[0033] The frequency F.sub.1 can then be compared to a frequency F.sub.0 that was sensed earlier. A frequency difference can then be determined via the difference between the frequencies F1 and F0.

[0034] By way of the proportionality discovered by the inventors between the frequency difference

[0035] DF and the change in the extension of the piston-cylinder arrangement 12, the change in the extension thereof can subsequently be determined.