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 a 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 configured to sense a capacitance of the piston-cylinder arrangement, applying a DC voltage to the piston-cylinder arrangement and to the electrical circuit unit, sensing the capacitance of the piston-cylinder arrangement as an input variable for the electrical circuit unit, generating a pulsed DC voltage by the electrical circuit unit on the basis of the sensed capacitance of the piston-cylinder arrangement, providing a measuring unit used to measure a frequency of the pulsed DC voltage generated, determining a frequency difference between the frequency of the pulsed DC voltage before displacement of the piston within the cylinder and the frequency of the pulsed DC voltage 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.

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 is applied to the cylinder and to the piston rod.

3. The method according to claim 1, 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 to be measured are in the range from 0.5 pF to 50 pF or 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. The method according to claim 1, wherein the pulsed DC voltage is generated on the basis of a discharge voltage that indicates the determined capacitance.

8. The method according to claim 1, wherein the DC voltage is applied to a resistor of the piston-cylinder arrangement.

9. A device for sensing a change in an 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, and an electrical circuit unit comprising a capacitance determination unit, which is configured to determine a capacitance of the piston-cylinder arrangement on the basis of a DC voltage, wherein the DC voltage is applied to the piston-cylinder arrangement and the electric circuit unit, wherein the electrical circuit unit is configured to generate a pulsed DC voltage on the basis of the determined capacitance of the piston-cylinder arrangement, the device further comprising: a measuring unit, which is configured to measure a frequency of the pulsed DC voltage generated, and an evaluation unit, which is configured to determine a frequency difference between the frequency of the pulsed DC voltage before displacement of the piston within the cylinder and the frequency of the pulsed DC voltage 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.

10. The device according to claim 9, 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 to the cylinder and to the piston rod.

11. The device according to claim 9, 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.

12. The device according to claim 9, wherein an outer tube is arranged on the cylinder and surrounds the cylinder.

13. The device according to claim 9, wherein capacitances (C) to be measured are in the range from 0.5 pF to 50 pF.

14. The device according to claim 13, wherein the capacitances (C) to be measured are in the range from 1 pF to 25 pF.

15. The device according to claim 9, wherein the piston-cylinder arrangement is a gas spring or a damper.

Description

(1) The present invention is described hereinafter with reference to the accompanying drawing, in which:

(2) FIG. 1 shows an electrical circuit unit that is connected to a piston-cylinder arrangement according to the present invention.

(3) 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.

(4) 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.

(5) 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:

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

(7) 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.

(8) By way of the proportionality discovered by the inventors between the frequency difference DF and the change in the extension of the piston-cylinder arrangement 12, the change in the extension thereof can subsequently be determined.