EP2476916A2 - Piston-cylinder unit with device for position tracking - Google Patents

Abstract

The unit (10) has a position determination device with an excitation unit e.g. oscillator (50) such as Hartley oscillator, which is directly or indirectly connected with a tubular hydraulic cylinder barrel (20) and electrical-conductively connected with a cylinder piston (30). The determination device is partially arranged within a cylinder housing or the barrel. An electrical resonant circuit formed from the unit and contact lines (40) is stimulated for oscillating at resonance frequency. An electric signal characterizing the resonance frequency is measured as measurable voltage at the unit.

Description

The present invention relates to a piston-cylinder unit with a device for position determination.

The position determination of a cylinder piston is a necessary and important task in a number of technical applications. In particular, the exact position of the cylinder piston often plays a major role in the targeted control of the piston-cylinder unit. In addition, the reliability of a piston-cylinder unit can be significantly increased by determining the position, since the inlet of the hydraulic medium, in particular the hydraulic fluid can be precisely controlled in the extreme positions of the cylinder piston and thus stopped in time.

Also, a precise position determination in the automatic control of the piston-cylinder units in construction equipment or lifting equipment is important. The piston-cylinder unit actuates in a conventional manner the working equipment of the construction machine or the lifting device. A sufficiently accurate position determination of the piston-cylinder unit increases the quality of the control and is therefore urgently needed.

The prevailing high control pressures within the piston-cylinder unit, which occur especially in hydraulic cylinder units, often allow only a slight modification of the piston or the cylinder jacket, without causing a safety-relevant impairment of the overall system. For this reason, the arrangement of a suitable position measuring device often designed as particularly difficult and expensive.

In many piston-cylinder units, the current position of the cylinder piston is detected by arranged pull-potentiometer.

Furthermore, methods are known which operate according to a magnetoresistive principle. Here, the position of the piston is detected by attaching a ring magnet at a certain piston position in combination with a built-in piston rod sensor.

All known methods, however, have in common that complex and costly modifications of the piston-cylinder unit are mandatory. Additional transducers or measuring sensors must be integrated into the piston-cylinder unit for the time being.

The object of the present invention is to provide a piston-cylinder unit with a position-determining device, which has a satisfactory stability and robustness and yet is easy and inexpensive to produce and install.

This object is achieved by a piston-cylinder unit with a device for position determination according to the features of claim 1. The piston-cylinder unit is preferably designed as a hydraulic cylinder and used as a hydraulic medium particularly preferably a hydraulic oil.

The device for position determination comprises at least one excitation means which is directly or indirectly electrically connected to the cylinder jacket and indirectly or directly to the cylinder piston of the piston-cylinder unit. Cylinder shell and cylinder pistons each act as an electrode of a series resonant circuit. The piston rod and the cylinder jacket form a series inductance. Opposing piston and cylinder surfaces with hydraulic media form a capacity. Accordingly, the complete piston-cylinder unit can be regarded as a resonant circuit.

The excitation means according to the invention serves to excite the electrical series resonant circuit for oscillation in its resonant frequency. The self-adjusting resonance frequency of a resonant circuit is basically due to the capacitance or inductance. Consequently, based on the resonant frequency, the variable capacity of the piston-cylinder unit can be deduced, the capacity and inductance depending on the current piston position. Thus, the actual and exact piston position can be determined from the resonance frequency. For this purpose, a further characteristic of the invention, a resonant frequency characterizing electrical signal on the device can be tapped.

The invention takes advantage of the fact that the piston-cylinder unit is suitable without modification for the formation of an electrical resonant circuit. In contrast to the prior art, no external sensors or measuring sensors or additional electrodes need to be arranged on or within the piston-cylinder unit. The known components of a piston-cylinder unit, such as the cylinder jacket and the cylinder piston are used to form a series resonant circuit.

Advantageously, the excitation means comprises an oscillator circuit which is electrically connected to the piston-cylinder unit. A particularly advantageous is a Hartley oscillator circuit.

The resonant frequency of the resonant circuit is classified as a high-frequency signal and experience has shown that it is in the megahertz range. The piston-cylinder unit can act as an antenna that emits electromagnetic waves. In this context, it may be expedient that advantageously at least a part of the device for determining the position is arranged within the cylinder housing or the cylinder jacket. In particular, the excitation means in the interior of the piston-cylinder unit or a dedicated cavity of the piston-cylinder unit is arranged. The shielding effect of the cylinder jacket has an advantageous effect on the EMC characteristics of the device or the piston-cylinder unit.

Alternatively, it can preferably be provided at least one additional shielding means, that the externally arranged device for position determination, in particular covers the excitation means and prevents the emission of the electromagnetic waves. An advantageous magnetic shield, which is made in particular of a ferromagnetic material turns out to be advantageous. Likewise, of course, other shielding materials are also conceivable which suitably cover and shield the device for determining the position. Furthermore, the use of at least one EMI filter proves to be advantageous.

Preferably, the signal to be picked off, which characterizes the resonant frequency, is an electrical voltage. This voltage has during the oscillation process of the piston-cylinder unit an oscillating waveform, advantageously is galvanically isolated, and used as a rectangular signal for digital evaluation.

Under certain circumstances, the vibration behavior is damped and influenced by the resonant circuit components or external influences. In order to keep the amplitude of the oscillation constant, a circuit device for stabilizing the tapped voltage may be advantageous. The external influences include moisture, dust deposits, etc. By this measure leaves stabilize the resonance frequency and allows a sufficiently accurate position determination.

Preferably, an evaluation means is provided, which is suitable for evaluating the signal and for outputting the present piston position. The evaluation means may be a correspondingly configured microcontroller or a suitable analogue circuit device. The evaluation is either permanently connected to the piston-cylinder unit or detachably connected to this.

In order to reduce the resonance frequency, an additional inductance between the excitation means and the piston or between the excitation means and the cylinder jacket can advantageously be arranged. This can be advantageous for EMC technical reasons.

The contact between the excitation means and the piston-cylinder unit is advantageously produced by a sliding contact. In particular, the contact between the movable part of the piston-cylinder unit, in particular the piston rod, is preferably realized by means of sliding contact. It proves useful brush contact between the piston rod and excitation means, the brush during the piston movement slides along the piston rod surface. The brush is preferably made of carbon, bronze or other suitable material.

Alternatively, the contacting between the piston rod and the excitation means can be effected by means of a capacitive or conductive ring. The ring is slidably disposed coaxially with the piston rod on the surface thereof. The use of a capacitive ring creates an additional constant capacitance connected in series with the tank circuit.

Preferably, the ring consists of a conductive material, which is directly or indirectly connected to the excitation means, wherein between the ring and piston rod, a dielectric is arranged or the conductive ring directly with the Piston rod is galvanically connected. Furthermore, insulation between the piston-cylinder unit and the oscillator or the excitation means can be achieved by inserting a transformer. The leakage inductance of the transformer can also be used to reduce the resonance frequency.

The present invention further relates to a construction machine or a lifting device with a piston-cylinder unit according to one of the preceding advantageous embodiments. The construction machine according to the invention or the lifting device obviously has the same advantages and properties as the above-described piston-cylinder unit, which is why at this point a further explanation is dispensed with.

The use of the piston-cylinder unit is by no means limited to construction machinery or lifting devices. Possible areas of application arise in aircraft or generally in all machines / devices with hydraulic / pneumatic technology.

Figur 1:

die erfindungsgemäße Kolben-Zylinder-Einheit mit einer Vorrichtung zur Positionsbestimmung,

Figur 2:

ein Schaltbild der erfindungsgemäßen Vorrichtung zur Positionsbestimmung,

Figur 3:

eine vorteilhafte Erweiterung der erfindungsgemäßen Kolben-Zylinder-Einheit,

Figur 4:

die erfindungsgemäße Kolben-Zylinder-Einheit mit einem zusätzlichen Abschirmungsmittel,

Figur 5:

eine alternative Ausgestaltung der erfindungsgemäßen Kolben-Zylinder-Einheit,

Figur 6:

die erfindungsgemäße Kolben-Zylinder-Einheit mit einem angeordneten kapazitiven Ring,

Figur 7:

eine Schnittdarstellung des kapazitiven Rings bzw. der Kolbenstange entlang der Schnittlinie A-A und

Figur 8:

eine weitere vorteilhafte Ausführung der erfindungsgemäßen Kolben-Zylinder-Einheit.

Further advantages and details of the invention are explained below with reference to the embodiments illustrated in the drawings. Show it:

FIG. 1:

the piston-cylinder unit according to the invention with a device for position determination,

FIG. 2:

a circuit diagram of the device according to the invention for determining the position,

FIG. 3:

an advantageous extension of the piston-cylinder unit according to the invention,

FIG. 4:

the piston-cylinder unit according to the invention with an additional shielding means,

FIG. 5:

an alternative embodiment of the piston-cylinder unit according to the invention,

FIG. 6:

the piston-cylinder unit according to the invention with an arranged capacitive ring,

FIG. 7:

a sectional view of the capacitive ring or the piston rod along the section line AA and

FIG. 8:

a further advantageous embodiment of the piston-cylinder unit according to the invention.

FIG. 1 shows the piston-cylinder unit 10 according to the invention with a device for position determination. The construction of the piston-cylinder unit 10 is similar to a known piston-cylinder unit. In detail, the unit 10 comprises a tubular cylinder jacket 20, in the cavity of which a piston 30 with arranged piston rod 31 is mounted linearly displaceable.

The piston-cylinder unit 10 is preferably used in construction machines or lifting devices, wherein a fixed implement is driven by the piston-cylinder unit 10. The automatic operation of the implement requires the precise positioning of the piston 30th

In order to enable an exact position determination, neither additional sensors, electrodes or transducers have to be installed on or in the piston-cylinder unit 10. Instead, the advantage is exploited that the entire piston-cylinder unit 10 acts by appropriate excitation as an electrical resonant circuit. In detail, the piston 30 forms a first electrode of a series resonant circuit and the cylinder jacket 20, the second electrode of the series resonant circuit. Neither the piston 30, nor the piston rod 31 are conductively connected to the cylinder jacket 20, but instead via seals between the piston 30 and cylinder shell 20 and in the opening region of the cylinder jacket 20th and the exiting piston rod 31 slidably mounted. Between the piston 30 and the cylinder jacket 20 is located in a hydraulic cylinder, a hydraulic medium, in particular hydraulic oil, which acts as a dielectric between the two electrodes.

To excite the resonant circuit is an oscillator 50, which is on the electrical lines 40 once with the cylinder jacket 20 and the piston rod 31 in conjunction.

After excitation of the resonant circuit via the oscillator 50, the oscillator oscillates at its resonant frequency. The formed impedance of piston 30 and cylinder shell 20 depends on the respective position of the piston 30 in the cavity of the cylinder. Since the capacitance or inductance of the resonant circuit influence the adjusting resonant frequency, a conclusion about the present impedance of the piston-cylinder unit 10 can be made on the basis of the detected resonant frequency.

For this purpose, a corresponding output voltage V _{out is} tapped off in the region of the oscillator 50 and analyzed or interpreted by a corresponding evaluation means, not shown, and optionally indicated optically or acoustically.

The electrical contact between the oscillator 50 and the movable piston rod 31 is realized by means of a sliding contact. The piston rod 31 facing the end of the connecting line 40 of the oscillator 50 has for this purpose a brush contact, which extends slidably on the surface of the piston rod 31. The brushes of this contact point are preferably made of carbon, bronze or other suitable material.

FIG. 2 shows a circuit diagram of the inventive piston-cylinder unit 10 with the corresponding interconnected device for determining position. The marked output voltage V _out has an oscillating signal course and accordingly describes the present resonance frequency of the entire resonant circuit. This voltage or the voltage curve changes depending on the corresponding piston position of the piston-cylinder unit 10th

In FIG. 3 is that out FIG. 1 known piston-cylinder unit 10 according to the invention, this being supplemented by an additional inductance between the oscillator 50 and the cylinder jacket 20. Since the resonant circuit formed oscillates in a high-frequency resonant frequency range, the resonant frequency can be significantly reduced by the additionally series-connected inductor 60.

Under certain circumstances, the application of the piston-cylinder unit 10 in construction equipment or lifting devices must meet high EMC requirements. As already mentioned above, particularly high-frequency oscillations occur in the arrangement according to the invention, which may possibly extend into the megahertz range. In order to meet the required EMC requirements, as in FIG. 4 installed, an additional shield 70 installed, which covers the area around the oscillator 50, and shields the released electromagnetic waves due to the antenna characteristics of the piston-cylinder unit 10 to the environment. Such a shield 70 is made of a ferromagnetic material, for example. Of course, all materials are conceivable that ensure adequate shielding of the electromagnetic waves.

In an advantageous embodiment, the cylinder jacket 20 can be misused as a shielding means. Like this FIG. 5 shows, the oscillator 50 is mounted in the cavity of the cylinder jacket 20. Furthermore, spark suppressors may be connected at the outputs of the oscillator 50.

As an alternative to the embodiment of the piston-cylinder unit with sliding contacts, the connection between oscillator 50 and piston rod 31 can be implemented by means of a capacitive or conductive ring 80. As in FIG. 6 shown, runs such a ring 80 coaxial with the piston rod 31 and slidably on the surface of the piston rod 31.

A sectional view along the section axis AA is the FIG. 7 refer to. This shows the capacitive ring 80, which is made of a conductive material. Between the piston rod 31 and the capacitive ring 80 is a dielectric 90. Ring 80 and piston rod 31 form a constant capacitance, which is connected in series with the resonant circuit.

The last figure ( FIG. 8 ) shows a possible decoupling of the oscillator 50 from the piston-cylinder unit 10. The electrical connection is made via a transformer 100. The internal inductance of the transformer 100 acts as an additional series-connected inductance of the resonant circuit, whereby the self-adjusting resonant frequency is further reduced. Furthermore, electrical isolation between the cylinder and the oscillator 50 is realized by the transformer 100.

Claims (12)

Piston-cylinder unit with a device for position determination, wherein the device comprises at least one excitation means, which is indirectly / directly electrically connected to the cylinder jacket and the cylinder piston of the piston-cylinder unit and the from the piston-cylinder unit and The resonant circuit formed for the oscillation of the resonant circuit formed in the contact lines excites the oscillation, wherein an electrical signal characterizing the resonant frequency can be tapped off at the piston-cylinder unit. Piston-cylinder unit according to claim 1, characterized in that the excitation means is an oscillator, in particular a Hartley oscillator. Piston-cylinder unit according to one of the preceding claims, characterized in that the device for determining the position at least is partially disposed within the cylinder housing or the cylinder jacket. Piston-cylinder unit according to one of the preceding claims, characterized in that the tappable electrical signal is a measurable voltage. Piston-cylinder unit according to claim 4, characterized in that a circuit device for stabilizing the tapped voltage or for maintaining the resonance oscillation is provided. Piston-cylinder unit according to one of the preceding claims, characterized in that an evaluation means for evaluating the tapped signal and optionally for output or representation of the piston position. Piston-cylinder unit according to one of the preceding claims, characterized in that at least one additional inductance between the excitation means and the piston or between the excitation means and the cylinder jacket is arranged. Piston-cylinder unit according to one of the preceding claims, characterized in that at least one additional shielding means, in particular made of ferromagnetic material, is provided for shielding the device. Piston-cylinder unit according to one of the preceding claims, characterized in that the electrical contact between the excitation means and the piston-cylinder unit, in particular the piston rod, takes place by means of a sliding contact. Piston-cylinder unit according to claim 9, characterized in that a capacitive ring is arranged around the piston rod as a sliding contact, which represents an additionally connected in series capacity within the resonant circuit. Piston-cylinder unit according to one of the preceding claims, characterized in that the excitation means is connected via a transformer with the piston-cylinder unit in connection. Construction machine or lifting device with a piston-cylinder unit according to one of claims 1 to 11.

Images