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EP-4196427-B1 - CONTROL OF A LIFTING DEVICE OF AN INDUSTRIAL TRUCK

EP4196427B1EP 4196427 B1EP4196427 B1EP 4196427B1EP-4196427-B1

Inventors

  • Laaksonen, Janne

Dates

Publication Date
20260513
Application Date
20210806

Claims (14)

  1. A method for controlling a lowering motion of a lifting device (120) of an industrial truck, characterized in that the method, performed by a control unit (210) of the industrial truck, comprises: determining (420) a weight of a load dependent control ramp, wherein the weight of the load dependent control ramp defines values of a control signal as a function of time to cause the lifting device (120) to reach its maximum lowering speed, the weight of the load dependent control ramp is determined (420) by: selecting the load dependent control ramp among a plurality of the weight of the load dependent control ramps; or generating the load dependent control ramp by scaling a reference control ramp in accordance with the weight of the load; and generating (430) at least one control signal to at least one valve (230) controlling at least in part the lowering motion of the lifting device (120), the at least one control signal carrying data corresponding to the weight of the load dependent control ramp.
  2. The method of claim 1, the method further comprising: determining (410) a weight of a load carried by the lifting device (120).
  3. The method of claim 2, wherein a determination of the weight of the load is performed by one of: obtaining measurement data from at least one sensor (240) configured to measure the weight of the load; obtaining data representing the weight of the load from data storage; obtaining a parameter from a lift motor being dependent of the weight of the load.
  4. The method of claim 2 or claim 3, wherein the determination of the weight is performed in response to a detection of a control signal causing an initiation of the lowering motion of the lifting device (120).
  5. The method of any of preceding claims, wherein the control ramp dedicated to the load having a weight in a first range is defined to allow reaching of a maximum speed of the lowering motion faster than the control ramp dedicated to the load having a weight in a second range.
  6. The method of claim 5, wherein the weight in the first range is less than the weight in the second range.
  7. A control unit (210) of an industrial truck for controlling a lowering motion of a lifting device (120) of an industrial truck, characterized in that the control unit (210) is configured to: determine (420) a weight of a load dependent control ramp, wherein the weight of the load dependent control ramp defines values of a control signal as a function of time to cause the lifting device (120) to reach its maximum lowering speed, the weight of the load dependent control ramp is determined (420) by: selecting the load dependent control ramp among a plurality of the weight of the load dependent control ramps; or generating the load dependent control ramp by scaling a reference control ramp in accordance with the weight of the load; and generate (430) at least one control signal to at least one valve (230) controlling at least in part the lowering motion of the lifting device (120), the at least one control signal carrying data corresponding to a weight of a load dependent control ramp.
  8. The control unit (210) of claim 7, the control unit (210) further configured to: determine (410) a weight of a load carried by the lifting device (120).
  9. The control unit (210) of claim 8, wherein the control unit (210) is configured to perform a determination of the weight of the load by one of: obtaining measurement data from at least one sensor (240) configured to measure the weight of the load; obtaining data representing the weight of the load from data storage; obtaining a parameter from a lift motor being dependent of the weight of the load.
  10. The control unit (210) of claim 8 or claim 9, wherein the control unit (210) is configured to perform the determination of the weight in response to a detection of a control signal causing an initiation of the lowering motion of the lifting device (120).
  11. The control unit (210) of any of preceding claims 7 to 10, wherein the control unit (210) is configured to define the control ramp dedicated to the load having a weight in a first range to allow reaching of a maximum speed of the lowering motion faster than the control ramp dedicated to the load having a weight in a second range.
  12. The control unit (210) of claim 11, wherein the weight in the first range is less than the weight in the second range.
  13. An industrial truck, the industrial truck comprising: a lifting device (120), at least one valve (230) controlling at least in part a lowering motion of the lifting device (120), and a control unit (210) according to any of claims 8 to 14.
  14. A computer program comprising computer readable program code configured to cause performing of the method according to any of claims 1 to 6 when said program code is run on a control unit (210) according to any of claims 7 to

Description

TECHNICAL FIELD The invention concerns in general the technical field of industrial trucks. More particularly, the invention concerns controlling of a lifting device of an industrial truck. BACKGROUND Industrial trucks are important devices for handling of loads e.g. in warehouses and similar. Figure 1 illustrates schematically an example of an industrial truck according to a prior art. The industrial truck may comprise a body part 110 and a lifting device 120. The body part 110 may comprise among other entities a motor for enabling a motion of the industrial truck and control devices for allowing a control of the industrial truck by an operator of the truck. The lifting device 120 may comprise a mast structure 130 along which a load tool 140 may be lifted and lowered in accordance with control operations performed by the operator of the truck. In Figure 1 the load tool 140 is so-called fork tool, but it may be selected in accordance with a type of load to be handled with the industrial truck. A control of a lifting operation and a lowering operation of the lifting device 120 are important tasks in view of an overall operation of the industrial truck. The lifting operation is typically performed so that the motor of the industrial truck is controlled to generate a force causing the lifting of the load tool 140 along the mast 130 through increasing a pressure in one or more hydraulic cylinders of the lifting device 120. Depending on the truck type the mast 130 may also be implemented so that it may be extended in order to reach higher heights during the operation of the industrial truck. During the lifting operation so-called lift cylinder is filled in with a hydraulic agent applied in a hydraulic implementation and an amount of the hydraulic agent in a cylinder is dependent on the height of the load tool 140 of the lifting device 120. Some non-limiting examples of the hydraulic agent used by applicable cylinders may e.g. be any applicable liquid, such as oil. Now, at some point the operator of the industrial truck generates a control operation to cause a lowering of the load tool 140. This may cause a generation of an electrical signal to an electrically actuatable valve which, in turn, causes a leakage of the hydraulic agent from the cylinder enabling the lowering of the load tool 140. In accordance with prior art solutions the controlling of the lowering valve is performed by pre-defining a control ramp, or a control curve, for the lowering valve in order to optimize a motion of the lifting device 120 during the lowering phase. Figure 2 illustrates schematically such a control ramp according to prior art wherein it is shown a control signal, i.e. a control current of the lowering valve, as a function of time. As may be derived from Figure 2 by increasing the control current to the lowering valve the lowering motion accelerates until the lowering valve reaches its maximum operational speed set for the lowering motion and by maintaining the control current steady the lifting device 120 may be caused to lower down at a steady speed. The solution according to prior art is a compromise and has a drawback that it does not operate optimally with different amounts of loads. For example, in some situations, especially with heavy loads, applying the control ramp as shown in Figure 1 may cause bouncing of the load during the lowering phase which is an undesired effect, and even dangerous at some instances. Documents WO 99/16698 A1 and WO 2016/160113 A2 describe methods for controlling a lowering motion of a lifting device and lifting devices that make use of such technology. WO 99/16698 discloses the features corresponding to the preamble of claim 1. Hence, there is a need to introduce novel approaches for handling of loads. SUMMARY The following presents a simplified summary in order to provide basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. An object of the invention is to present a method, a control unit, an industrial truck and a computer program for controlling a lifting device The objects of the invention are reached by a method, a control unit, an industrial truck and a computer program for controlling a lifting device as defined by the respective independent claims. According to the invention, there is provided a method for controlling a lowering motion of a lifting device of an industrial truck, the method, performed by a control unit of the industrial truck, comprises: determining a weight of a load dependent control ramp, wherein the weight of the load dependent control ramp defines values of a control signal as a function of tim