The invention relates to a method and apparatus for a pressing process according to the preambles of the independent claims related thereto.

The invention is especially suited for use of a so called waste compactor, when e.g. waste being fed to a waste container is condensed by pressing it together in the waste container by a electro-hydraulic press. Thus, a pressing force produced by a pump used by an electric motor is accomplished controlled e.g. by a so called programmable logic by using a pressurized hydraulic fluid brought to a hydraulic cylinder arrangement via solenoid valves .

Traditionally the location of a pressing piston of a press in extreme positions of its pressing and releasing movements are being determined with mechanical limit switches, regulated by which the electric motor using the pressing piston is being controlled by a contactor operating on on-off- principle. In addition, at present, a waste container's degree of fullness is typically being monitored in a corresponding manner by using e.g. so called pressure switches. Use of an electric pressure motor with on-off-principle produces strong pressure strokes to the hydraulic arrangement every time the pressing piston's movement direction is being changed abruptly with solenoid valves. Naturally this also causes sudden load peaks in the electric network when the pressing motor starts. In addition, the type of limit switches described above get easily damaged due to circumstances in practice, which is why they have been abandoned when possible, as is also the case with pressure switches monitoring the waste container's degree of fullness. Today, the above described mechanical sensors are often replaced with pressure sensors connected to the hydraulic arrangement, in which case the extreme positions of the pressing piston are recognized and the progress of pressure in the pressing stage (i.e. the degree of fullness of the waste container) is monitored by the pressure sensors based on pressure information determined from the hydraulic system.

In addition, waste compactors today are typically used by electric motors with an output of ~ 4-5,5 kW that require three-phase supply according to the exemplary electric schematic diagram shown in figure 2. The pressing motor is expected to have a high power so that the pressing process may be carried out as fast as possible. Because providing a sufficient speed requires a large flow, it therefore requires a so called direct control electric motor and a pump with an efficient production. In a pressing process functioning on direct control, the change of the pressing piston's movement direction typically causes a power surge as high as 20 A to the electric motor, which a 16 A slow fuse, however, endures. With a single phase socket, however, more than 3,68 kW of current may not be plugged in nowadays, which is why an electric motor with single- phase input and based on direct control may not be used satisfactorily in the type of a pressing process described above, because the power of the electric motor may thus not exceed 3,68 kW according to present regulations .

Furthermore, it is typical in the present waste compactors, in order to make the pressing together of the waste mass more efficient, that a pressing piston in the end of its pressing movement executes a pre-set amount of so called press-release-cycles, usually 2-5 depending on the circumstances. The amount of pressing cycles is, however, very dependent on the quality of the mass to be pressed, when in certain practical situations a higher amount of these kinds of compressing cycles are needed, when instead in some cases they would practically not be needed at all.

As a summary of the worst defects regarding prior art may among other things be mentioned the following:

- waste compactors strain mechanically due to the abrupt movements caused by the electric pressing motor's on-off usage, which movements wear out both mechanical and hydraulic joints, and

- the waste compactor requires a three-phase input, which does not easily enable utilization of e.g. direct current stored in an accumulator unit in the power input of the pressing process. This is due to the fact that when direct current is converted into three-phase current to be used by the electric motor in the pressing process, three converting circuits for alternating current are needed, in -addition to which they must function in a synchronized manner, so that a right phase difference is obtained between the phases.

Improving the present on-off functioning waste compactors based on the three-phase current technically, would be possible e.g. in the following ways :

- by using a "pressure accumulator" in the hydraulic system in order to reduce pressure strokes, an additional expense of which, however, is considerable, as it, on the other hand, also increases the risk of accidents in malfunction/maintenance situations,

- controlling the use of a three-phase electric motor with a so called soft starter, which is an additional piece of equipment that causes additional costs and maintenance requirements. A soft starter limits current taken by the electric motor in the starting phase, in which case starting of the electric motor takes place more softly. This kind of implementation does not work well, if the electric motor has a high load right after it has started, which can easily occur e.g. due to the freezing temperatures in the winter, when oil is stiff, or in some practical pressing situations, such as e.g. when the waste compactor's logic starts the pressing piston's movement, when the same is already in the extreme position of its pressing movement. Generally soft starter does not suit to constant starting, either, which may be the case especially in a waste compactor that is used a lot.

In order to replace a three-phase input, there are nowadays also single-phase electric motors available, but the maximum limit set for the single-phase current that is e.g. in Finland 3 , 68 k at present, makes the waste compactor so slow that it is not possible to make an efficient enough entirety out of it only by using it with direct control. It is an aim of the method and apparatus for a pressing process according to the present invention to achieve a decisive improvement in the problems described above and thus to raise essentially the level of prior art. In order to carry out this aim, the method and apparatus according to the invention are mainly characterized by what has been presented in the characterizing parts of the independent claims related thereto . As the most important advantages of the method and apparatus for a pressing process according to the invention may be mentioned simplicity and efficiency of the functioning of the pressing process made possible by the method and apparatus and the appliances suited for the same, when first of all the pressing process may be significantly eased due to enabling the processing to be carried out with single-phase current instead of three-phase current thanks to the frequency inverter principle utilized in the invention.

As to the frequency inverter principle, the functioning of a frequency inverter is based on semiconductor technique. The frequency inverter rectifies alternating current coming from an electricity network into direct current. There are two main types of frequency inverters: the ones with an intermediate circuit and straight ones. In the ones with an intermediate circuit, alternating current is firstly converted into direct current and then back to alternating current with a desired frequency. In the straight type, incoming alternating current is chopped with semiconductor switches directly into alternating current with a desired frequency. At present, frequency inverters with an intermediate circuit are more common in practice. Therefore, e.g. direct current converted into an intermediate circuit of a frequency inverter with an intermediate circuit is proportioned in three- phases by three fast semiconductor circuits according to the desired functioning of the motor. In a frequency inverter at present there may also be integrated a so called programmable logic, such as e.g. a microprocessor control, in which information of the motor and parameters having impact on its desired functioning are set. In addition, it may nowadays even be programmed with a machine control, whereby a separate logic control unit is not needed. Because the frequency inverter rectifies the supply voltage, there are in practice single-phase functioning models available that are, however, used to control a normal three-phase motor having the lowest acquisition cost. Frequency inverters are able to follow the behavior of the phases of the motor and "listen to" the motor's load situation and its actual rotation speed. By adjusting phase differences and currents, torsion of the motor may be enhanced while, however, keeping the rotation speed in a desired value. Because the speed of the motor is based on the frequency of the supply voltage, it may, according to need, be steplessly adjusted even higher than the electric motor's nominal speed, whereby, however, the driving torque of the electric motor decreases in practice.

As an advantageous embodiment in practice, in the invention there has been utilized a programmable frequency inverter with a single-phase input and a nominal power of 2,2 kW, a three-phase motor with a corresponding power and correspondingly, as a pump, one with e.g. 3/5 of the output of a traditional 5,5 kw pump. The entirety described above would practically produce sufficient pressing pressure even though operating on direct control, but the overall time taken by the pressing process would become too long. The frequency inverter usage utilized in the invention enables use of an electric motor both at higher and lower speeds than its nominal speed in specific phases of the pressing process. Because torsion of the motor, however, decreases as the revolutions rise, there must not be too much pressure response at higher speeds. In the use of a frequency inverter this may be compensated so that, with higher pressure responses, the electric motor's basic speed is decreased thus causing its driving torque to rise and simultaneously keeping its supply current within desired limits.

Furthermore, as advantageously executed, the control arrangement used in the process is based on indirect measuring of the pressure response, because the current taken by the electric motor is sufficiently comparable to the pressure produced by the pump. Thanks to this, it is possible to leave out traditional pressure transmitters, such as also a separate logic control unit, from the pressing process according to the invention, in addition to which the electric motors and pump utilized in the invention may be executed with cost effective standard components. Therefore, thanks to the invention, significant saving of costs are made possible due to both "lighter" machinery and ad ustment/control technique.

The invention also enables use of renewable energy, such as e.g. solar panels, wind or water/wave energy in an easy and reliable manner e.g. by using rechargeable accumulator units, because, when utilizing the invention, there is only need for one converting circuit for alternating current, such as an inverter arrangement or the like. Thanks to the invention, the accumulator system is not subject to load peaks exceeding its capacity.

In the following description, the invention is being illustrated in detail with reference to the appended drawings, in which: in figure 1

is show a simplified operating principle of an embodiment of the method according to the invention in one of its advantageous utilizing purposes in connection with a waste compactor, in figure 2

is shown an electric circuit diagram of use of a traditional electric motor with three- phase supply, in figure 3

is shown exemplary electric circuit diagram of use of an advantageous single-phase electric motor enabled by the invention, and in figure 4

is presented a parallel comparison of exemplary pressing processes executed traditionally and according to the invention.

The invention relates first of all to a method for a pressing process, such as for use of a waste compactor or the like, wherein a pressing force needed in the pressing process is being produced by action of an electric press motor 1 by using a mechanical drive assembly or preferably a pressure medium operated such as hydraulic pump arrangement 2 being coupled to a pressure medium system, whereby the medium pressurized by the same, such a hydraulic fluid, is being directed through a valve arrangement 3 , such as by one or more solenoid valves or the like, into an actuator cylinder arrangement 4, such as one or more hydraulic cylinders, in order to move an actuator 5 carrying out the pressing, such as a pressing piston or the like, with a pressing movement occurring in one direction and a return movement occurring in the opposite direction. The pressing process is being carried out in a controlled manner by a programmable logic 6, such as one or more micro-processors, logic circuits and/or the like, and mechanical, electric and/or pressure medium operated monitoring means 7 coupled therewith. E.g. in the method utilized in a waste compactor use according to figure 1, frequency inverter principle is being exploited particularly in order to enable use of the press motor 1 in a steplessly adjustable manner and depending on the situation/circumstances with a speed both lower and higher than its nominal speed. It is naturally also possible to use a mechanical drive assembly instead of the pump arrangement 2 in order to move the actuator 5, e.g. by rotating a screw with the press motor by a speed reducer, by means of which the pressing piston is being moved in the pressing process.

As an advantageous embodiment of the method according to the invention especially with reference to the exemplary electric circuit diagram shown in figure 3, in the method, as a frequency inverter arrangement X, a frequency inverter is being exploited that is operable by a single-phase input, applicable for single-phase current by its nominal output and provided with a programmable logic 6, especially as the press motor 1, a three-phase motor with an output corresponding essentially to the same of the frequency inverter X and, as the pump arrangement 2, one or more pumps, the output of which corresponding essentially to the same of the three-phase motor.

Therefore, thanks to the invention e.g. a waste compactor may be connected to the electricity network with a normal contact plug with protective grounding supply, in addition to which, there is such an advantage that the network is not subject to sharp load peaks . As a furthermore advantageous embodiment of the method, in the end of the pressing actuator's 5 pressing movement one or more brief releasing-pressing-cycles are being carried out by the same in order to make the pressing phase more efficient.

As a further advantageous embodiment, extreme positions of the actuator's 5 pressing and return movements are being recognized and/or the pressure response during its pressing movement are being monitored by monitoring means 7; 71, 7b, whereby the movement speed of the pressing actuator 5 during its pressing movement and/or the amount of the repeated releasing-pressing-cycles is/are being adjusted on grounds of the pressure response during the pressing movement, being recognized by the monitoring means 7.

As a furthermore advantageous embodiment of the method, in the return movement of the pressing actuator 5 and/or, when the pressure response of the same during its pressing movement is less than a pre-set limit value set for the same, the press motor 1 is being driven by the frequency inverter arrangement X with a higher speed than its nominal speed.

Furthermore, as an advantageous embodiment of the method, when a higher pressure response than the preset limit value set for the same is being recognized during the pressing movement of the pressing actuator 5, the speed of the press motor 1 is being adjusted by the frequency inverter arrangement X steplessly into an optimum torque zone in order to perform the pressing with an essentially lower speed than the pressing motor's 1 nominal speed.

As a furthermore advantageous embodiment of the method, at a switch moment of the movement direction of the pressing actuator's 5 pressing movement and/or return movement, the press motor 1 is preferably being stopped e.g. for an adjustable/pre-set length of time, whereafter a stepless acceleration of the press motor 1 is being initiated by the frequency inverter arrangement X into a higher speed of the press motor than its nominal speed.

The method according to the invention furthermore enables use of solar, wind, water/wave energy and/or the like to be charged into an accumulator unit, whereby the direct voltage produced is being converted e.g. by an inverter arrangement into alternating voltage for using one or more electric motors belonging to the pressing process. The invention also relates to an apparatus for a pressing process, such as for use of a waste compactor or the like, executed according to the invention, which apparatus consists of: an electric press motor 1 for producing a pressing force needed in the pressing process; a mechanical drive assembly or preferably a pressure medium operated, such as hydraulic pump arrangement 2 being coupled to a pressure medium system, whereby the medium pressurized by the same, such a hydraulic fluid, is directed through a valve arrangement 3, such as by one or more solenoid valves or the like, into an actuator cylinder arrangement 4, such as one or more hydraulic cylinders, in order to move an actuator 5 carrying out the pressing, such as a pressing piston or the like, with a pressing movement occurring in one direction and a return movement occurring in the opposite direction; and a programmable logic 6, such as one or more microprocessors, logic circuits and/or the like, and mechanical, electric and/or pressure medium operated monitoring means 7 coupled therewith. According to figure 1, the apparatus exploited in a waste pressing process includes, with reference to the exemplary electric circuit diagram shown in figure 3, a frequency inverter arrangement X particularly in order to enable use of the press motor 1 in a steplessly adjustable manner and depending on the situation/circumstances with a speed both lower and higher than its nominal speed. As an advantageous embodiment of the apparatus according to the invention, the frequency inverter arrangement X belonging thereto comprises a frequency inverter that is operable by a single-phase input, applicable for single-phase current by its nominal output, advantageously with a power of 2,2 kW, and provided with a programmable logic 6. Therefore, thanks to the invention e.g. a waste compactor may be connected to the electric network with a normal contact plug with protective grounding, in addition to which, there is such an advantage that the network is not subject to sharp load peaks.

Therefore, the press motor 1 comprises advantageously a three-phase motor with an output corresponding essentially to the same of the frequency inverter X, and the pump arrangement 2 correspondingly one or more pumps, the output of which corresponding essentially to the same of the three-phase motor.

As a furthermore advantageous embodiment of the apparatus according to the invention, the monitoring means 7; 71, 7b for recognizing extreme positions of the actuator's 5 pressing and return movements and/or for monitoring pressure response during its pressing movement, being coupled with the programmable logic 6 of the frequency inverter arrangement X, are arranged to operate directly by monitoring the pressure of the pressure medium system or most advantageously indirectly by monitoring the current of the press motor 1.

In this case, furthermore advantageously, when a higher pressure response than the pre-set limit value set for the same is being recognized during the pressing movement of the pressing actuator 5, the frequency inverter arrangement X adjusts the speed of the press motor 1 steplessly into an optimum torque zone in order to perform the pressing with an essentially lower speed than the pressing motor's 1 nominal speed. Correspondingly, when the pressure response of the pressing actuator 5 during its pressing movement is less than a pre-set limit value set for the same, the frequency inverter arrangement X adjusts the speed of the press motor 1 by increasing it to a higher speed than its nominal speed. In the appended diagram 4 are shown exemplary process diagrams of the functions of both traditionally and according to the invention executed pressing processes . According to said diagram, the programmable logic controlling the pressing process according to the invention starts the electric motor softly and accelerates the speed of the same steplessly e.g. to 1,7 times higher than its nominal speed while the pressing piston's movement is free, i.e. without significant pressure response. When a load is detected

(i.e. with a pressure response higher than what is preset) , the electric motor's speed is dropped steplessly to an optimal torque zone and the pressing piston's pressing/turning movements are made with the electric motor's decreased speed, e.g. 0,6 x its nominal speed.

In this way, pressure strokes and other mechanical strains caused by abrupt movements may be avoided. The supply current of the electric motor stays constantly under 12 A during the whole pressing process. When the turning moment comes, as an advantageous embodiment the electric motor is stopped and after that its soft i.e. stepless acceleration to a higher speed is started, until according to a pre-set timing, the electric motor's speed is again decreased just before the turning moment. In case during the pressing a need is detected for one or more release-press-cycles, such will be started next.

It may be proven with calculations that compared to a traditional three-phase 5,5 kw motor, thanks to the invention, with a 60% smaller motor (2,2 kW) it is possible to produce 68% of its performance. Correspondingly with a 45% smaller motor (3,0 kW) it is possible to produce with a one-phase input according to the invention 100% of a three-phase 5,5 kW motor's capacity. It is clear that the invention is not limited to the embodiments shown or described above, but instead it can be modified in various ways to fit the needs of each utilization purpose and embodiment surrounding etc. within the limits of the basic idea of the invention. Therefore, it is first of all clear that in the practical executions of the method according to the invention, numeral alternative technical arrangements and processing logics, such as e.g. a straight type frequency inverter with integrated or separate programmable logics or the like may be utilized. In addition, it is possible to exploit the use of a frequency inverter with any kind of actuator associated with a pressing process, such as e.g. in a waste feeding lift used in connection with a waste container, directing solar panels to an optimal position etc., because with the use of the frequency inverter, all the appliances associated with a pressing process may be easily attached. In addition, it is naturally clear that e.g. the logic of the pressing process shown in figure 4, may be executed in a different manner e.g. according to the needs of the electric motor being used, in optimum drive speeds in each situation with accelerating/slowing down the electric motor steplessly or when needed with certain progressive steps etc.