SYSTEM FOR OPERATING A FLUID ACTUATOR

Description

[0001] The invention relates to a system for operating a fluid actuator, in particular a system for adjusting / varying the stroke of a piston comprised in the fluid actuator.

[0002] In injection molding machines, taken here as an example, molten material is injected into a mold through one or more injection nozzles whose opening and closing is regulated by one or more stems controlled by an actuator. For complex or large parts, produced by multi-injection and / or sequential injection methods, the positional control of the shutter, which opens and closes the nozzle, is essential to obtain a high quality of finish, in particular to control the flow of molten material together with the injection pressure in the mold cavity. Currently, for the molding of valuable products, shutters are controlled by electric actuators (because they allow a wide range of adjustments and controls), which however require complex and expensive control devices (an electronic control unit + related software + sensors + complex wiring + specialized operators). The use of fluid actuators is therefore more convenient and more familiar to users for certain applications, see e.g. the system in Fig. 2 in EP3490777 which - commonly - uses a three-way solenoid valve 20 to control an actuator 1 via a fluid circuit.

[0003] A problem is that in case of sudden power voltage failure or in case of emergency, the solenoid valve 20 moves to the central rest position (position determined / set by the action of springs 220 and 230), locking the shutter in the current position and leaving the injection channel open. Clearly, this creates a potentially dangerous situation as well as considerable damage to the injection system.

[0004] EP 2 556 941 A1, WO 2014 / 153330 A1, US 2007 / 059397 A1, US 2006 / 070378 A1, JP S61 128017 U and US 2020 / 180201 A1 disclose solenoid-valve-actuated systems.

[0005] The main object of the invention is to improve this state of the art.

[0006] Another object is to improve systems such as the one in EP3490777 by making them safer, in particular by allowing the shutter to be repositioned in the closed position in the event of an electrical power failure.

[0007] An aspect of the invention relates to a system comprising: an actuator that is provided with a piston movably mounted to be moved linearly by the thrust of a fluid within two chambers separated by the piston, a needle shutter connected to the piston to regulate the injection flow of molten material from one or more nozzles into a mold, so that the shutter can move from a closing position, wherein there is no passage of molten material through the nozzle, to an opening position, wherein there is passage of molten material through the nozzle, a supply circuit for bringing pressurized fluid from a reservoir to the chambers with a flow direction and an opposite direction, the two fluid flow directions corresponding to a forward and a backward movement of the piston, respectively, and a solenoid valve, connected to the supply circuit and configured so that in rest condition it leaves open a fluid drainage path that connects the chambers and the reservoir to allow a flow of fluid, between the chambers and the reservoir, which causes a movement of the piston aimed at bringing the shutter towards a, or the, closing position.

[0008] A plurality of needle shutters may be connected to the piston, to be moved by the piston in synchronism.

[0009] The solenoid valve is inserted directly into the path of the supply circuit.

[0010] In particular, the solenoid valve comprises two excitation positions: a position wherein it allows fluid communication between the chambers and the reservoir by imposing in the supply circuit a flow direction for the fluid opposite to that obtainable in the rest position, and a position wherein it inhibits fluid communication between the chambers and the reservoir.

[0011] Or two solenoid valves may be inserted directly into the supply circuit path, each with an excitation position wherein they allow fluid communication between the chambers and the reservoir by imposing in the supply circuit a flow direction for the fluid opposite to that obtainable from the other solenoid valve.

[0012] The fluid may be a liquid, such as oil, or compressed air.

[0013] The advantages of the invention will be even clearer from the following description of a preferred system, in which reference is made to the accompanying drawing in which• Figure 1 shows a scheme of the system.

[0014] The system MC2 of Fig. 1 is used to drive an actuator 10. The actuator 10 is attached to a support, such as a hot runner (manifold) or a plate or mold, and is used to move (directly or indirectly, through interposed motion transformation mechanisms - not shown) at least one needle shutter 12 for an injection nozzle (not shown) by means of a piston 14. The piston 14 is linearly movable within a cavity defined by a housing 16. The cavity is divided by the piston 14 into a first chamber 20, communicating with a port 22, and a second chamber 24, communicating with a port 26. The chamber 20 is typically isolated from the chamber 24; however, situations may arise in which it is necessary to provide means for connecting the two chambers.

[0015] Through the fluid ports or inlets 22, 26, fluid, e.g. oil or compressed air, can be injected or extracted into / from the chamber 20 or 24 on opposite sides of the piston 14, respectively, so as to be able to move the latter linearly in opposite directions moving the shutter 12 accordingly. The movement of the shutter 12 determines the opening or closing of the nozzle with consequent passage or obstruction of the molten material.

[0016] The opening and closing of the nozzle, and therefore the movement of the shutter (pin), can take place according to a single movement in both directions (trend with a single opening ramp and a single closing ramp) or can comprise multiple and different intermediate stops (pauses of movement, according to pre-established parameters, after which the movement resumes according to the previous parameters (speed, pressure, flow rate, etc.....) or according to modified parameters). It is possible to achieve infinite pauses of movement according to infinite positions, during the opening or closing movement.

[0017] A fluid circuit allows fluid to be transferred to and from the chambers 20, 24 by pumping it from an external reservoir (not shown, e.g. a tank). The circuit comprises a first line 30 and a second line 32. Optional flow regulators 40, 42 are also comprised in the lines 30, 32, which allow, in addition to a homogeneous movement, the setting of different movement speeds of the piston 14 along its stroke.

[0018] The flow regulators 40, 42 may be manually or automatically activated. In the latter case, they may be adjusted according to predetermined positions or on the basis of positional feedback given by appropriate position sensors (not shown) for the shutter or the piston.

[0019] A solenoid valve 70, having a displaceable drawer 72, is used to reverse, at each complete cycle, the direction of fluid flow in the lines 30, 32. The flow direction determines the movement direction of the piston 14, and thus of the shutter 12, during the opening or closing.

[0020] The drawer 72 is electrically switchable between two excitation positions: in a first position, some fluid can travel along the line 30 toward the chamber 24 and some fluid can travel along the line 32 exiting the chamber 20, and in a second position the fluid flow is inhibited.

[0021] At rest, the solenoid valve 70 remains in a position wherein it allows fluid to flow through the line 32 to the chamber 20 and out of the chamber 24 to the reservoir via line 30.

[0022] It is understood that the system MC2 is inherently safe thanks to the solenoid valve 70, which in the event of an anomaly, or in the absence of voltage, automatically configures (or trips) so that a flow of fluid is possible in the lines 30, 32 to bring the shutter 12 to the closing position.

[0023] Note that in order to obtain the same dynamic profile for the shutter 12, the sequence of commands sent to solenoid valve is in particular:to raise the shutter 12 and open the channel for the molten material, the solenoid valve 70 is energized to bring it in the first position; to lower the shutter 12 and close the channel, the solenoid valve 70 is de-energized; to hold the shutter 12 in intermediate position, the solenoid valve 70 is energized to move the latter in the second position.

[0024] In general, the solenoid valve 70 is energized for holding the shutter 12 in the intermediate position, and moving the shutter 12 only in one direction.

[0025] The solenoid valve 70 may be replaced by a pair of two-way solenoid valves that have a same resting configuration.

[0026] In both cases, by an appropriate management of the opening or closing positions of the piston's supply circuits, thus the different positions of the solenoid valves together with possibly the adjustment of the flow regulators, the invention as described allows making / implementing one or more of the opening and / or closing profiles described and shown in the following documents: PCT / IB2019 / 053936, IT102017000037002, IT102016000080198, IT102016000055364, IT102015000008368, ITTO2014A001030, ITTO2014A001021, ITTO2014A000701, WO2012 / 074879A1, WO2012 / 087491 A1 and WO2018 / 020177A1

[0027] The invention is set out in the appended set of claims.

Claims

1. System (MC2) comprising: - an actuator (10) that is provided with a piston (14) movably mounted to be moved linearly by the thrust of a fluid within two chambers (20, 24) separated by the piston (14), - a needle shutter (12) connected to the piston (14) for regulating the injection flow of molten material from a nozzle into a mold, so that the shutter can move from a closing position, wherein there is no passage of molten material through the nozzle, to an opening position, wherein there is passage of molten material through the nozzle, and vice versa; - a supply circuit (30, 32) for bringing pressurized fluid from a reservoir to the chambers (20, 24) with a flow direction and an opposite flow direction, the two fluid flow directions corresponding to a forward and a backward movement of the piston (14), respectively; and - a solenoid valve (60; 70), connected to the supply circuit (30, 32) and configured so that in resting condition it leaves open a fluid drainage path that connects the chambers (20, 24) and the reservoir to allow a flow of fluid between the chambers (20, 24) and the reservoir determining a movement of the piston that brings the shutter to a closing position, wherein the solenoid valve (70) • is inserted directly into the path of the supply circuit (30, 32), and characterised in that the solenoid valve (70) • comprises two excitation positions: - a position wherein it allows fluid communication between the chambers (20, 24) and the reservoir by imposing in the supply circuit a fluid flow direction opposite to that obtainable in the rest position, and - a position wherein it inhibits fluid communication between the chambers (20, 24) and the reservoir.

2. System (MC2) according claim 1, wherein the fluid is a liquid.

3. System (MC2) according claim 2, wherein the fluid is oil.

4. System (MC2) according claim 1, wherein the fluid is compressed air.

5. Method for controlling a system according to any one of the preceding claims, wherein to raise the shutter (12) and open the channel for molten material, the solenoid valve (60; 70) is energized, to lower the shutter (12) and close the channel for molten material, the solenoid valve (60; 70) is de-energized, and to hold the shutter (12) in a intermediate position, the solenoid valve (60; 70) is energized