METHOD FOR LIFTING LOAD WITH VACUUM GRIPPING APPARATUS

Abstract: The invention relates to a method for lifting a load, such as a paper roll (1), with a vacuum gripping apparatus (2), whereby a pressure lower than the ambient pressure is sucked into a suction space arrangement (5) between the upper surface of the load and the vacuum gripping apparatus, and whereby the lifting capacity of the vacuum gripping apparatus is proportional to the pressure difference thus produced. In accordance with the invention the required pressure difference limit is set load-specifically on the basis of load information available in advance.

Description: METHOD FOR LIFTING LOAD WITH VACUUM GRIPPING APPARATUS BACKGROUND OF THE INVENTION The invention relates to a method for lifting a load, such as a paper roll, with a vacuum gripping apparatus, whereby a pressure lower than the at- mospheric pressure is sucked into a suction space arrangement between the upper surface of the load and the vacuum gripping apparatus, and whereby the lifting capacity of the vacuum gripping apparatus is proportional to the pressure difference thus produced. The pressure difference achieved by the pump of the vacuum grip- ping apparatus is also proportional to the displaced volume flow. When sucking a paper roll, air still leaks through the roll, whereby the pressure difference remains inferior to a leakless ideal case. As regards different types of paper rolls, the pressure difference achieved varies considerably. In a general case, when the roll is being gripped it occurs that upon the suction command the pressures in a vacuum chamber and the suction space arrangement stabilize. Thereafter the pump is capable of raising the pressure difference. After a while the pressure difference reading stabilizes at a level determined by the leakage in the roll, the level being lower than the original pressure difference of the chamber. In vacuum gripping apparatuses designed for lifting tight or nearly tight paper rolls an impeller pump is used for producing vacuum, the impeller pump being able to produce a great pressure difference for lifting rolls as heavy as possible. In a conventional structure, the gripping apparatus is provided with a pressure switch that is adjusted to permit the lifting of the roll if the pressure difference is sufficient for lifting a roll used as a design load. This roll is naturally the heaviest of the rolls to be lifted in view of the suction surface. When tight, heavy rolls and loose, light rolls are handled in the same warehouse, for a roll the vacuum gripping apparatus is not able to produce the pressure difference required for a lifting permission. This is not al- ways possible even by increasing the output of the vacuum pump by changing the pump for a bigger one in the system, since the overall dimensions of the pump have certain limits. On the other hand, it is not possible to change a pump type, since in that case the pressure difference needed for lifting heavy rolls is lost. BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to avoid the above-described drawbacks. This is achieved with the method of the invention, which is mainly characterized in that the required pressure difference limit is determined load- specifically on the basis of load information available in advance. Thus, a plurality of different load types can be lifted safely with the same vacuum gripping apparatus, whereby, for instance, in the above- described warehouse of two paper types a lower pressure difference is used for obtaining a lifting permission for a loose, light roll, and a higher pressure difference for a tight, heavy roll. It is possible to use a load-specific lifting permission limit, for instance, in a warehouse where the paper rolls are stocked in vertical position, since the paper quality and roll measurements of each roll entering the warehouse are known, which values are entered into a stock computer. On the ba- sis of the paper quality and roll measurements the lowest safe pressure difference can be calculated for lifting the roll concerned. Preferably the stock computer informs PLC, controlling the operation of the vacuum gripping apparatus, of this pressure difference (or its code), the PLC granting a lifting permission to a lifting machinery of the vacuum gripping apparatus, when the informed pres- sure difference is realized. At simplest, this system is used, for instance, in a warehouse where usually tight rolls, and occasionally loose rolls, are stocked. Most advantageously, a plurality of pressure difference limits are set in the system, whereby apart from a paper type, different values are used for rolls of different dimen- sions. For instance, it is thus possible to lift heavier rolls than before by setting the required pressure difference permission to the extreme limits of the equipment, when a heavy roll awaits longer the rise in pressure difference, which does not, however, substantially delay the handling of other rolls in the warehouse. Moreover, for monitoring defective rolls, security and state of the system it is most advantageous that the developing of vacuum and the maintaining of the pressure difference achieved is controlled after the suction command. BRIEF DESCRIPTION OF THE DRAWINGS In the following the invention will be described by means of one preferred embodiment with reference to the attached drawings, in which Figure 1 is a simplified schematic view of the method of the inven- tion and of a vacuum gripping apparatus to be used in the method, and Figure 2 illustrates stabilization of pressure difference in the system in proportion to time. DETAILED DESCRIPTION OF THE INVENTION In Figure 1 the method of the invention is described by means of a simplified schematic view in connection with a paper roll warehouse, where paper rolls 1 to be lifted are stocked in vertical position. A vacuum gripping apparatus 2 used in the method comprises in the lowest position a vacuum chamber 3 whose lower surface acts as a suction plate. Concentric circles of sealing tape 4 are provided onto said lower surface, which circles together with the end of the roll 1 form circular suction spaces 5 constituting a suction space arrangement. The number of suction spaces 5 formed naturally depends on the diameter of the roll 1. In the centre of the sealing tape circles 4 there is a downward centering cone 6, which is intended to cooperate with the centre hole 7 of the paper roll 1 for centering the vacuum gripping apparatus 2 in the midpoint of the end of the roll 1. On top of the vacuum chamber 3 there is a vacuum equipment 8, communicating with said vacuum chamber, the equipment comprising a vacuum pump and necessary accessories (not shown in the drawings). A control system 9 for controlling the operations of the vacuum equipment 8 and the vacuum cham- ber 3, and for measuring the pressures in the vacuum chambers 3 and suction spaces 5 are arranged on top of the vacuum equipment 8. Pressure measuring means comprise low pressure transmitters which measure pressure difference between the pressure to be produced and the ambient (atmospheric) pressure. A reference numeral 10 indicates a framework of the vacuum grip- ping apparatus 2. This framework 10 comprises, among other things, guiding columns 11 for positioning into a swing preventing clamp. When lifting the roll 1 , the vacuum gripping apparatus 2 is placed by means of lifting ropes13 of its lifting machinery 12 onto the end surface of the roll 1 guided by the centering cone 6, and when the lifting ropes13 are found slack, the PLC 14 of the lifting machinery gives the PLC 15 of the vacuum gripping apparatus a lifting command. Consequently, vacuum is sucked by means of the vacuum chamber 3 and the vacuum equipment 9 into the suction spaces 5 that are formed with the end surfaces of the roll 1. The produced vacuum compared with the ambient pressure is measured with vacuum trans- mitters (not shown in the drawings) in the suction spaces 5 and the vacuum chamber 3, which communicates with the suction spaces 5 in suction phase. Necessary information (paper quality and roll measurements) for determining the required roll-specific pressure difference is received from a stock computer 16 whereby the required pressure difference limit is calculated in the stock computer 16 itself or possibly in the PLC 15. When the required pressure difference is achieved after a certain waiting time, the PLC 15 gives the lifting machinery 12 of the vacuum gripping apparatus 2 a lifting command. If the waiting time exceeds the set limits, the roll 1 is released and an error is reported. As stated above, after the suction command the pressures in the vacuum chamber 3 and in the suction space arrangement 5 stabilize. Thereafter the vacuum equipment 8 is able to increase the pressure difference. In accordance with the Figure 2, after a while the pressure difference reading stabilizes at the level determined by the leakage of the roll 1 , the level being lower than the initial pressure of the chamber 3. As distinct from a tight roll, after the stabilization of pressures, the pressure difference curve of a loose roll shows a gently declining part before the graph becomes even and turns upwards. Normally, the declining part indicates a phase in which the suction penetrates the roll. However, as long as the pressure falls, it is impossible to make sure, whether the roll is a typical loose roll, or whether the roll or the sealings (e.g. sealing tapes 4) of the vacuum gripping apparatus 2 have a defect causing leakage. In connection with the present invention the development of vacuum is preferably monitored after the suction command. The pressure differ- ence is then measured both in the suction spaces 5 and the vacuum chamber 3. The PLC 15 software monitors the stabilization of the pressure on the basis of measurement results. The roll 1 can be lifted if the pressure difference value is sufficient. If the pressure does not stabilize within a certain period of time, the roll is found defective and it is rejected. It is advisable to monitor and measure the pressure difference all the time when the roll 1 is exposed to the suction effect of the vacuum gripping apparatus. If the pressure difference starts falling later on, the control notices that. It is important that this occurs before the actual lifting permission limit is broken, so that there is more time to lower the roll 1 back to the ground. The above description of the invention is only intended to illustrate the invention. However, a person skilled in the art may implement its details in a variety of alternative ways within the scope of the appended claims.

Claims: CLAIMS 1. A method for lifting a load, such as a paper roll (1), with a vacuum gripping apparatus (2), whereby a pressure lower than the ambient pressure is sucked into a suction space arrangement between the upper surface of the load and the vacuum gripping apparatus, and whereby the lifting capacity of the vacuum gripping apparatus is proportional to the pressure difference thus produced, characterized in that the required pressure difference limit is set load-specifically on the basis of load information available in advance. 2. A method as claimed in claim 1, used for lifting paper rolls (1) stocked in a warehouse where the paper rolls are in vertical position, characterized in that information on the paper quality and dimensions of the roll (1) stored in a stock computer (16) is utilized for calculating the required pressure difference. 3. A method as claimed in claim 2, characterized in that the required pressure difference is calculated in the stock computer (16) which informs PLC (15) controlling the operation of the vacuum gripping apparatus (2) of the obtained result, the PLC granting a lifting machinery (12) a lifting permission, when the informed pressure difference is realized. 4. A method as claimed in claim 2, characterized in that the required pressure difference is calculated in the PLC (15) or in the vacuum gripping apparatus (2) according to the information received from the stock computer (16). 5. A method as claimed in claim 1, characterized in that the development of vacuum is monitored after the suction command. 6. A method as claimed in claim 5, characterized in that the pressure difference is monitored and measured in the suction space arrangement (5) of the vacuum gripping apparatus and in the vacuum chamber (3), which communicate with one another in suction phase 7. A method as claimed in claim 5, characterized in that the pressure difference is monitored all the time when the load is exposed to the suction effect of the vacuum gripping apparatus (2).

Inventors: HAKKARAINEN SIMO, LINDBERG TEPPO, SORSA TIMO, HAKKARAINEN, SIMO, LINDBERG, TEPPO, SORSA, TIMO
Applicants: HAKKARAINEN SIMO, KCI KONE CRANES INT OY, LINDBERG TEPPO, SORSA TIMO, HAKKARAINEN, SIMO, KCI KONECRANES INTERNATIONAL CORPORATION, LINDBERG, TEPPO, SORSA, TIMO
Application year: 1998
Main classification: B66C1
IPC codes: B65G47, B66C1