EP3978420A1 - Method for damping mast torsional vibration in an industrial truck and industrial truck - Google Patents

Abstract

The invention relates to a method for damping lifting mast torsional vibrations in an industrial truck, in particular a reach truck, with a load handling device comprising a lifting mast with at least two mast profiles for picking up a load, the load center of a picked-up load being laterally displaceable by means of a side shift device, which is Control device is controlled. It is proposed that a sensor system (S) be used to determine elastic deformations of the mast profiles, with a torsion value being formed from the difference in the elastic deformations of the various mast profiles, which is fed back to the control device (C) in a closed control circuit and used for active damping of the lifting mast - Torsional vibrations are used by adapted control of the sideshift device (P). Furthermore, the invention relates to an industrial truck for carrying out the method.

Description

The invention relates to a method for damping lifting mast torsional vibrations in an industrial truck, in particular a reach truck, with a load handling device comprising a lifting mast with at least two mast profiles for picking up a load, the load center of a picked-up load being laterally displaceable by means of a side shift device, which is Control device is controlled.

The invention also relates to an industrial truck for carrying out the method.

Industrial trucks include, for example, forklifts, in particular counterbalanced forklifts, and reach trucks. Such industrial trucks are equipped with a load handling device for stacking and storing goods to be transported. The load handling device usually includes a lifting mast with at least one mast profile. As a rule, two mast profiles which are arranged parallel to one another and are laterally spaced apart from one another are provided with a vertical orientation. The lifting mast can also be provided with a tilting device, so that the mast profiles can be tilted against the vertical. A load carriage, in particular a fork carriage, on which forks are typically mounted, can be vertically displaced on the mast profiles, e.g. by means of a lifting cylinder device of a working hydraulic system, and thus raised and lowered. A load can be picked up on the forks, for example via a pallet. A side shift device is also often provided, with which the center of gravity of the load picked up can be shifted to the side. For this purpose, for example, the load carriage can be shifted laterally in relation to the mast profiles of the lifting mast by means of a side shift cylinder.

When picking up or putting down heavy loads at a high lifting height, the problem of vibrations of the lifting mast arises. While this behavior is not very noticeable in counterbalanced forklifts, it is reach trucks rather superficially and disturbingly. Compared to counterbalanced forklifts, reach trucks usually have much higher mast profiles and hardly any components that can absorb and dissipate the vibration energy. For example, reach trucks usually have no rubber tires and a mast connection without rubber buffers.

For this reason, assistance systems have been developed for reach trucks that actively dampen occasional mast vibrations.

However, these systems are designed exclusively for absorbing forward and backward pitching vibrations of the lift mast, which are primarily caused by driving the load onto or off the rack or pushing the lift mast in the longitudinal direction of the industrial truck, but not for absorbing the lift mast - Torsional vibrations about the vertical axis, which are primarily excited by the operation of the sideshift device. In order to eliminate the pitching vibrations of the lifting mast, the vibration damping is carried out by actively intervening in the mast extension function - i.e. in the longitudinal direction. Such an intervention possibility is unsuitable for the damping of torsional vibrations of the lifting mast.

Systems with active damping of the lifting mast torsional vibrations in a closed circuit are not previously known. A pre-controlled, model-based control of the side shift device is known, based on the essential variables lifting height and load weight, which is designed to minimize the torsional vibrations of the lifting mast after the side shift device has been actuated. Typically, a pre-control filter is used for this, the transfer function of which is based on the inverse function of the transfer function of the controlled system, and strives for the best possible open-loop compensation of the poles and zeros of the controlled system.

The disadvantages of such a pre-controlled active damping of the lifting mast torsional vibrations are poor performance with small deviations between model and reality and the fact that no damping of unforeseeable excitations is possible. These can occur, for example, by releasing a torsional preload when picking up the load in the rack and by contact with the rack or with other pallets during operation.

In industrial trucks, torsional vibrations of the lift mast about the vertical axis may not be as obvious as pitching vibrations of the lift mast forwards and backwards, but when they occur, torsional vibrations of the lift mast about the vertical axis are virtually undamped and therefore take a long time to subside.

The present invention is based on the object of designing a method of the type mentioned at the outset and an industrial truck for carrying out the method in such a way that torsional vibrations of the lifting mast can be reliably damped in all operating situations.

In terms of the method, this object is achieved according to the invention in that elastic deformations of the mast profiles of the lifting mast are determined by means of a sensor system, with a torsion value of the lifting mast being formed from the difference in the elastic deformations of the various mast profiles of the lifting mast, which is fed back to the control device in a closed control loop and to the active damping of the mast torsional vibrations is used by adapted control of the sideshift device.

A closed control loop is therefore provided, which enables a targeted, active counter-reaction when detecting lifting mast torsional vibrations about the vertical axis. For this purpose, elastic deformations are measured in both main mast profiles of the lifting mast. The lifting mast usually comprises two mast profiles which are aligned in parallel and are laterally spaced apart from one another. In this case, the elastic deformations are measured in both mast profiles. A torsion of the lifting mast about the vertical axis can be inferred from a difference in the elastic deformations in the various mast profiles. For example, a torsion value can be formed from the difference between the bending moments of the mast profiles detected by the sensors.

According to a particularly preferred embodiment of the invention, a lateral torsional offset is used as the torsional value. Instead of a torsion angle and its first and second derivatives, the resulting lateral torsional offset is used.

Expediently, the control device specifies a sideshift speed setpoint for a sideshift speed.

In a particularly advantageous embodiment of the invention, it is provided that the torsion value is fed back proportionally to the side shift speed setpoint in a closed control loop with an inverted sign. If a lateral torsional offset is used as the torsional value, then even a small offset can be actively counteracted with the sideshift device, as a result of which torsional vibrations of the lifting mast can be effectively damped from the start.

Strain sensors are preferably used as sensors to detect the elastic deformations of the mast profiles, with at least one strain sensor being provided on each mast profile.

In this case, strain gauges, so-called strain gauges, are expediently used as strain sensors. The use of strain gauges is in itself a proven method of measuring stress and strain. Strain gauges are used in a wide variety of applications to indirectly determine forces via strain measurement.

A particularly advantageous embodiment of the invention provides that the torsion value is determined from the difference in signals from the strain sensors on the different mast profiles.

The measurement is preferably carried out continuously, so that the current torsion value can be determined at any time.

A high-pass filter is advantageously used to form the torsion value.

A predetermined amplification factor is preferably applied when the torsion value is fed back in the closed control loop to the control device. The resulting gains refer to the momentary considered operating point, in particular with a given lifting mast, a given lifting height and a given load center.

The invention also relates to an industrial truck, in particular a reach truck, for carrying out the method with a load-handling device comprising a lifting mast with at least two mast profiles for picking up a load, and a side shift device, which is operatively connected to a control device, for laterally shifting the load center of a picked-up load.

In the case of the industrial truck, the object is achieved in that a sensor system is provided that is designed to determine elastic deformations of the mast profiles of the lifting mast and to form a torsion value of the lifting mast from the difference in the elastic deformations of the various mast profiles of the lifting mast, and a closed one Control loop is provided, which includes a feedback of the torsion value of the lifting mast to the control device, and the control device is set up to adapt the control of the side shift device to the torsion value of the lifting mast for active damping of the torsional vibrations of the lifting mast.

The sensor system expediently includes strain sensors, with at least one strain sensor being arranged on each mast profile.

The strain sensors are preferably designed as strain gauges.

• Eine bessere und einfachere Bedienung beim Abnehmen und Absetzen der Last in großer Hubhöhe. Die Folgen sind
  1. a) eine Entlastung der Bedienperson und
  2. b) eine höhere Umschlagsleistung des Flurförderzeugs.
• Mehr Sicherheit, weil schwingende Lasten in großer Hubhöhe über eine längere Zeit ein gewisses Gefährdungspotential implizieren.
• Eine Entlastung von Komponenten, beispielsweise der Mastrollen und der Mastprofile, da die Belastungen durch die Hubmasttorsion viel schneller abklingen.

The advantages of the active damping of lifting mast torsional vibrations according to the invention include the following points:

• A better and easier operation when removing and depositing the load at high lifting heights. The consequences are
  1. a) relief for the operator and
  2. b) higher handling capacity of the industrial truck.
• More safety, because swinging loads at high lifting heights imply a certain risk potential over a longer period of time.
• A relief of components, such as the mast rollers and the mast profiles, since the loads from the mast torsion subside much faster.

Figur 1

ein Signal-Flussdiagramm zur Modellierung der Seitenschub-Funktion und

Figur 2

ein Signal-Flussdiagramm zur Modellierung der Seitenschub-Funktion mit der erfindungsgemäßen, aktiven Schwingungsdämpfung.

Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiments illustrated in the schematic figures. show here

figure 1

a signal flow diagram for modeling the sideshift function and

figure 2

a signal flow chart for modeling the sideshift function with the active vibration damping according to the invention.

In the figure 1 a signal flow chart for modeling the sideshift function of a sideshift device of an industrial truck is shown. A control device (controller) C specifies a desired sideshift speed value for a sideshift speed y′ _des (desired shift speed) of the sideshift device (plant) P. In an actuator A of the sideshift device, the sideshift target value is converted into a target value for a cylinder speed y' cyl for a _sideshift cylinder. The second derivative _y " and the first derivative y' of the lateral position of the load center of a picked-up load in space and hence the resulting sideshift speed y' (resulting shift speed).

Instead of the torsion angle and its first and second derivatives, the resulting lateral torsional offset δy (elastic deflection) and the first and second derivatives y' and y" of the lateral position of the load center in space are used. There is a quasi-linear relationship between the angles small amplitude and lateral offset The resulting amplifications relate to the currently considered working point, in particular for a given lift mast, a given lift height and a given load center.

The controlled system can be simplified as a typical second-order mass spring system whose damping is directly dependent on the torsional velocity δy' via amplification with the amplification factor k _dp (passive damping). The problem here is that the gain k _dp is very low and causes the system to be very weakly damped (extremely weak).

the figure 2 shows the signal flow diagram for modeling the sideshift function from the figure 1 with the active vibration damping according to the invention.

The invention is based on the following consideration:
Hydraulic systems, such as forklift hydrostats that work with hydraulic oil, are often dampened by leakage effects. The damping effect is created by a certain proportionality between the size that builds up the force, for example a high oil pressure, and a (parasitic) reduction in the speed requirement, for example an oil flow.

If the sideshift cylinder were to give way under the torsional load as a result of leakage effects in the adjustment, then a damping effect would arise. Since this parasitic stabilizing effect is not provided by the lateral shifter itself, the invention is based on the idea of simulating it electronically.

For this purpose, according to the present exemplary embodiment of the invention, it is provided that the torsion of the lifting mast due to the torsional vibration is detected as a torsional offset δy (elastic deflection) by means of a sensor system S from the difference in the signals from two strain sensors, one of which is attached to a mast profile of the lifting mast is. The value of the torsional offset δy (elastic deflection) is returned proportionally with an inverted sign to the sideshift speed setpoint for the sideshift speed y′ _des (desired shift speed). An active amplification factor k _da (active damping) is used.

Claims (12)

Method for damping lifting mast torsional vibrations in an industrial truck, in particular a reach truck, with a load handling device comprising a lifting mast with at least two mast profiles for picking up a load, the load center of a picked-up load being laterally displaceable by means of a side shift device (P) which is controlled by a control device (C) is controlled, characterized in that elastic deformations of the mast profiles are determined by means of a sensor system (S), with a torsion value being formed from the difference in the elastic deformations of the various mast profiles, which is fed back to the control device (C) in a closed control loop and is used for active damping of the mast torsional vibrations through adapted activation of the sideshift device (P). Method according to Claim 1, characterized in that a lateral torsional offset (δy) is used as the torsional value. Method according to Claim 1 or 2, characterized in that the control device (C) specifies a sideshift speed setpoint for a sideshift speed (y' _des ). Method according to Claim 3, characterized in that the torsion value is fed back proportionally with an inverted sign to the sideshift speed setpoint for the sideshift speed (y' _des ) in a closed control loop. Method according to one of Claims 1 to 4, characterized in that strain sensors are used as the sensor system (S), with at least one strain sensor being provided on each mast profile. Method according to Claim 5, characterized in that strain gauges are used as strain sensors. Method according to Claim 5 or 6, characterized in that the torsion value is determined from the difference between signals from the strain sensors on the different mast profiles. Method according to one of Claims 1 to 7, characterized in that a high-pass filter is used to form the torsion value. A method as claimed in any one of Claims 1 to 8, characterized in that a predetermined amplification factor (k _da ) is applied when the torsion value is fed back in the closed control loop to the control device (C). Industrial truck, in particular reach truck, for carrying out the method according to one of Claims 1 to 9, with a load handling device comprising a lifting mast with at least two mast profiles for receiving a load, and a sideshift device (P) which is operatively connected to a control device (C) for lateral shifting of the center of gravity of a load that has been picked up, characterized in that a sensor system (S) is provided which is designed to determine elastic deformations of the mast profiles and to form a torsion value from the difference in the elastic deformations of the various mast profiles, and a closed control loop is provided, which includes feedback of the torsion value to the control device (C), and the control device (C) is set up to adapt the activation of the sideshift device (P) to the torsion value for active damping of the torsional vibrations of the lifting mast. Industrial truck according to Claim 10, characterized in that the sensor system (S) comprises expansion sensors, with at least one expansion sensor being arranged on each mast profile. Industrial truck according to Claim 11, characterized in that the strain sensors are in the form of strain gauges.

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