CONTROL SYSTEM AND METHOD OF AN INJECTION MOLDING APPARATUS OF PLASTIC MATERIALS

Abstract

A system and method for controlling an actuator which actuates an axially displaceable pin valve of an apparatus for injection molding of plastic materials, where the control system includes an electronic control unit of the actuator which adjusts at least one among position, speed and acceleration of the pin valve, and a position sensor which detects a position of a plunger of the actuator and is operatively connected to the electronic control unit. The position sensor indirectly detects the position of the plunger of the actuator.

Claims

1. A method for controlling an actuator which actuates an axially displaceable pin valve of an injector in an apparatus for injection molding of plastic materials, wherein the actuator is a fluid jack having a cylinder and a plunger and wherein an electronic control unit of the actuator adjusts at least one among position, speed and acceleration of the pin valve of the injector, the method comprising: a position sensor operatively connected to said electronic control unit and configured to (i) indirectly detect a position of the plunger of the actuator at a remote position, and (ii) detect and signal any leakages of a fluidic circuit of the actuator.

2. The method of claim 1, wherein the position sensor is operatively associated to a movable member actuated simultaneously with the actuator and includes a plunger of an auxiliary fluid jack.

3. The method of claim 2, wherein the fluidic circuit of the actuator includes a delivery and discharge circuit of the actuator, and wherein the plunger of the auxiliary fluid jack is inserted in the delivery and discharge circuit.

4. The method of claim 1, wherein the position sensor comprises a linear position transducer operatively associated to the plunger of the auxiliary fluid jack.

5. The method of claim 1, further comprising the position sensor being configured for detecting an end of stroke movement of the pin valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

[0014] FIG. 1 is a diagram showing the application of the position sensor according to the invention to a first example of an electrical-hydraulic circuit for the actuation of an actuator of an injector,

[0015] FIG. 2 is a diagram similar to FIG. 1 of a second example, and

[0016] FIG. 3 is a sectional schematic view of an embodiment of the position sensor.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Initially referring to FIG. 1, following is a summary description of an example of a control system of an injector of an apparatus for injection molding of plastic materials, comprising—in a per se known manner (and thus not illustrated in detail)—a nozzle in which the pin valve is axially displaceable between an advanced full closing position and a receded maximum opening position of the flow of the plastic material from a hot runner to the cavity of a mold. Generally, an apparatus thus made can for example be of the type described and illustrated in the previously mentioned document US-2015/0158227.

[0018] The displacement of the pin valve of the injector is obtained by means of a fluid actuator A including a cylinder a and a plunger b whose stem c is directly or indirectly connected to the pin valve of the injector. The actuator A, pneumatic or hydraulic, is of the double-acting type and it is connected to a delivery line P and to a return line T of a pressurised fluid, which mutually invert alternatingly depending on the displacement direction of the plunger b of the actuator and thus of the pin valve of the injector. The fluid, in the hydraulic case described herein, is supplied and discharged by a distribution unit schematised by section Y of the circuit, in turn connected to the delivery P and discharge T (section Z). The section Y may take various configurations, schematically illustrated, as a function of the needs and requests of the user of the molding apparatus.

[0019] Arranged between the actuator A and the distribution section Y are three sections B, C and E, all connected to a programmable electronic control unit D.

[0020] The section B includes a block solenoid valve by means of which the actuator A, and thus the pin valve of the injector, can be stopped in at least one intermediate position between the full closing position and the maximum opening position.

[0021] The section E includes a flow rate adjustment solenoid valve by means of which it is possible to control the displacement speed of the plunger b of the actuator A, and thus the speed of the pin valve of the injector. In the example described herein, the section E allows to adjust the displacement of the pin valve at a single constant speed, programmable by means of the control unit D.

[0022] The section B comprises a block solenoid valve which, upon command by the control unit D, stops the stroke of the plunger b of the actuator A, and thus the stroke of the pin valve of the injector, in at least one intermediate position between the full closing and maximum opening positions.

[0023] The section C, interposed in this case between the sections B and E, includes—according to the invention—a position sensor generally indicated with S which indirectly detects the position of the plunger b of the actuator A, and thus of the pin valve of the injector.

[0024] The expression indirect is used to indicate, in the description and in the claims that follow, the fact that the position sensor S is separated from the actuator A and it can thus be arranged in a remote position and spaced from the hot runner: for example on the mold, or on board the pressing machine or even outside the pressing machine of the molding apparatus.

[0025] As illustrated in detail in FIG. 3, the position sensor S consists of an auxiliary hydraulic circuit consisting of a cylinder 1 displaceable in which is a plunger 2 which delimits—in the cylinder—two chambers each of which is provided with a respective inlet/outlet 3, 4 connected to the hydraulic circuit of the actuator A. A linear position transducer 5, comprising a stem 6 slidable on which is an annular displaceable contact 7 carried by the plunger 2, is operatively connected to the electronic control unit D for indicating the position of the plunger 2 and thus, indirectly, the position of the pin valve of the injector.

[0026] The inlets/outlets 3, 4 of the auxiliary fluid jack S are connected—as mentioned—to the hydraulic circuit of the actuator A by means of a solenoid valve provided for in the section C, also controlled by the electronic control unit D, as outlined hereinafter.

[0027] Upon filling the hydraulic circuit, the solenoid valve of the section C is opened by the electronic unit D to allow the fluid to enter into the two chambers of the auxiliary hydraulic jack S filling them with oil and emptying them of air. At the end of this step, the solenoid valve of the section C is shut.

[0028] Subsequently carried out is a reset step, during which the actuator A is actuated to take the plunger b and thus the pin valve of the injector to the full closing position and then to maximum opening position, so as to respectively identify the origin and the maximum of the displacement. This step offers the possibility of being able to use the same position sensor S in molding systems provided with different actuators A.

[0029] During the normal regime operation, the hydraulic circuit oil will flow with reciprocating motion displacing the plunger 2 of the auxiliary hydraulic jack S proportionally to the stroke of the plunger b of the actuator A. The transducer 5 will detect the instantaneous position of the plunger 2 transmitting the relative signal to the electronic control unit D which will process it and use it to manage the electric controls of the various solenoid valves of the circuit so as to control the position, the speed and possibly the acceleration of the pin valve of the injector in a programmed fashion.

[0030] The variant of the hydraulic diagram represented in FIG. 2 is analogous to the embodiment described with reference to FIG. 1 and it differs from the latter solely due to the fact that the section E is configured so that the displacement speed of the pin valve adjusted by the electronic unit D can be double instead of single.

[0031] The advantages deriving from the invention, and specifically in that the position sensor S is physically separated from the actuator A, are summarised hereinafter: [0032] maximum flexibility, due to the possibility of being able to adapt to different types of actuators, of any size and manufacturing, [0033] possibility of remote-positioning and thus not affected by the high temperatures of the hot runner of the apparatus, [0034] possibility for the position sensor S to also serve as an end-stroke for the actuator A, [0035] capacity to detect and signal even possible leakages in the fluidic circuit of the actuator A, [0036] possibility of subsequently implementing, i.e. application of the electronic control even to previously existing molding apparatus, without having to directly intervene on the actuator of the or of each injector.

[0037] Obviously, the construction details and the embodiments, in particular as regards the configuration of the position sensor and relative transducer described above by way of example, may widely vary with respect to what has been described and illustrated, without departing from the scope of protection of the present invention as described in the claims that follow.

[0038] In particular, the indirect detection at a remote position could be actuated—instead of by means of the plunger of the auxiliary hydraulic jack—by a different mechanical device or device of any other nature, known to a man skilled in the art, capable of performing the same function.