JPH0251379B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention detects the pressure exerted on the cavity surface of a mold by a molten resin injected into the cavity of a mold of a resin injection molding machine. , relates to a resin injection molding machine that adjusts the injection time according to the pressure to prevent molded product defects due to excessive or insufficient injection.

[Prior art] In a resin injection molding machine, the injection process from when molten resin is injected into a mold cavity until it is smoothly filled with a predetermined amount of molten resin, and the transition to the next pressurizing process. Let's think about the process of doing so.

Conventionally, the injection process has been controlled by time or injection amount. Specifically, there is a method in which the injection cylinder automatically moves to the next pressurizing process when t seconds have elapsed since the injection cylinder first moves forward, or a method in which the injection cylinder moves to the next process when the injection cylinder moves forward by a predetermined stroke length. The injection process was controlled using . However, the optimum injection time changes due to the combined effects of various conditions such as variations in the viscosity of the molten resin, variations in the temperature of the mold, and variations in the extrusion speed. For this reason, in a control method using a fixed injection time or a fixed injection amount, if the injection time is shorter than the optimal injection time at that time, product defects will occur due to shot shot, and if the injection time is longer than the optimal injection time at that time. However, there was a problem in that burrs were generated at the joints of the molds, increasing manufacturing time and causing material loss.

[Problems to be Solved by the Invention] Therefore, the present invention improves the performance of the resin injection molding machine by detecting the pressure exerted by the molten resin on the cavity surface and controlling the injection process according to the pressure. The purpose is to increase

[Means for Solving the Problems] The present invention includes a molding die having a cavity, a heating cylinder that heats molten resin, and a mold that is inserted into the heating cylinder and rotates and reciprocates within the heating cylinder. , a resin injection molding machine comprising: a screw for injecting molten resin into the mold; an injection cylinder for driving the screw; a drive device for driving the injection cylinder; and a control device for controlling the drive device. In this, the control device includes a molding pressure detector disposed on a cavity surface of the molding die to detect molding pressure received from the molten resin injected into the cavity; a second pressure setting section that sets a second reference pressure smaller than the first reference pressure; and a signal from the molding pressure detector and the first pressure setting section. a first comparator unit that outputs a signal to that effect when the molding pressure is higher than the first reference pressure; and signals from the molding pressure detector and the second pressure setting unit. a second comparison unit that outputs a measurement start signal for measuring the subsequent elapsed time when the molding pressure becomes equal to the second reference pressure;
From the time when the signal is input from the second comparison section,
a timer unit that measures time and outputs a signal to that effect after a predetermined time elapses; and a timer unit that inputs signals from the first comparison unit and the timer unit, and when either one of the signals is input, the injection and a logic circuit for outputting a control signal to the driving device to stop the internal pressure in the cavity and maintain the internal pressure at the secondary pressure.

The molding pressure detector is a detector that detects the pressure received from the molten resin injected into the cavity of the molding die, and outputs a signal in accordance with the pressure. As the sensor of the pressure detector, for example, a pressure transducer element that outputs an electrical signal in response to applied pressure is desirable. The concept of the reference pressure and comparison section will be explained below with reference to FIG. In FIG. 1, the horizontal axis shows the time since the start of injection of the molten resin into the cavity, and the vertical axis shows the molding pressure P that the cavity surface receives from the molten resin. The first reference pressure is the first critical power that ends the injection of the molten resin and allows the transition to the next secondary pressurization process, and is P1 in the figure.
is the value of In the case of solid line graph 1, the first critical pressure is reached at time t3, and the pressure shifts to the secondary pressure.

The second reference pressure is a second critical pressure indicating a necessary condition for a product molded by injection to be molded as a good product, and is the value of P2 in the figure. The solid line graphs in the figure reach the pressure P2, which is the second reference pressure, at times t1 and t2, respectively. The pressure P2 indicates the pressure when the resin contacts the pressure detector. The pressure P1 is a pressure necessary to sufficiently spread the resin into the cavity and apply sufficient pressure.

The first and second pressure setting sections are respectively configured to
This is a device for setting the second reference pressure, and the setting method may be analog or digital.

The first comparison unit is a device that outputs a signal to allow transition from the injection process to the secondary pressurization process when it is confirmed that the molding pressure has reached the first reference pressure P1. .

The second comparison section is a device that outputs a signal indicating the start of time measurement when it is confirmed that the molding pressure P has reached the second reference pressure P2. The second comparator outputs a time measurement start instruction signal at times t1 and t2 in the solid line 1 and broken line 2, respectively.

The timer is a device that inputs a signal instructing to start timekeeping from the second comparator and outputs a signal permitting transition to the next secondary pressure pressurization process after a predetermined period of time has elapsed. For example, if a predetermined time is TO, then in the case of solid line graph 1, the measured time T1 is the TO
Since the molding pressure P reaches the first reference pressure by the time the molding pressure P reaches the first reference pressure, the molding pressure P is shifted to the second pressurizing step before the shift permission signal is input. In the case of broken line graph 2, when the measured time T2 becomes equal to the TO, a shift permission signal is output from the timer, and the injection process shifts to the next process.

As the main circuit components of the first and second comparison sections and the time measurement section, for example, a digital comparator, a microcomputer, etc. can be used.

The logic circuit is a circuit that outputs a signal when a signal from either the first comparison section or the time measurement section is input, and includes an OR circuit or an OR element,
Alternatively, OR connection method etc. can be used.

The meaning shown in FIG. 1 is explained with respect to the solid line 1 and the broken line 2. In the former case, the apparatus of the present invention starts the next secondary pressurization process as soon as the molding pressure reaches the first reference pressure. In the latter case, the molding pressure does not reach the first reference pressure, but after a predetermined time TO has elapsed after the molding pressure exceeds the second reference pressure, the secondary pressure pressurization step is performed. Controls the transition to That is, in both the former and latter cases, the transition to the next step is controlled in the minimum time.

Molten resin is inserted into the screw inside the heating cylinder,
A heating cylinder heats the molten resin, a drive device drives an injection cylinder, and the injection cylinder moves the screw toward the mold. In response to the movement, the screw starts injecting the molten resin into the cavity of the mold.

The molding pressure detector receives pressure from the molten resin, and outputs a signal corresponding to the pressure that changes every moment according to the injection to the first and second comparing sections. The first and second pressure setting sections set first and second reference pressures, respectively, before starting the molding cycle.
They are output to the first and second comparison sections, respectively.

The first comparison section inputs signals from the molding pressure detection section and the first pressure setting section, and when the molding pressure becomes equal to or higher than the first reference pressure, the first comparison section switches from injection to the next step. Outputs a signal to clarify. The second comparing section inputs and compares signals from the molding pressure detector and the second pressure setting section, and outputs a signal instructing to start timing when the molding pressure becomes equal to or higher than a second reference pressure.

When the timekeeping section receives the signal from the second comparison section, it starts timekeeping, and when a predetermined time elapses,
Outputs a signal to clearly indicate this.

The logic circuit inputs signals from the first comparison section and the time measurement section, and outputs a control signal instructing to proceed to the next step when either one of the signals is input.

[Examples] Hereinafter, the present invention will be explained in detail based on specific examples. FIG. 2 is a block diagram illustrating the characteristic parts of the present invention of a control device for a resin injection molding machine according to a specific embodiment, and FIG. 3 is a block diagram that further embodies the block diagram in FIG. 2. be. The configuration of the apparatus of this embodiment will be described below with reference to FIGS. 2 and 3.

In the following explanation, the flip-flop circuit,
The OR circuit, transistor, comparator, and inverter element are respectively FF, OR, TR,
Abbreviated as COMP, INV. Also, regarding signal terminals, input and output terminals are IN, OUT, and
Regarding signal levels, high and low levels are abbreviated as H and L, respectively.

The main body of the resin molding machine consists of a heating tube 1, a screw 2,
It consists of an injection cylinder 3 and a drive device 4. The molding die 5 is composed of a lower mold 6 and an upper mold 7, and has a cavity 8.

The molding pressure detector 10 is composed of a pressure transducer element 11 whose output terminal has an electrical resistance that changes depending on the pressure received from the molten resin, and an amplifier 12 which processes the detected signal. As a specific circuit, the third
The detection unit 110 shown in FIG.
, the pressure transducing element 11, and a power supply 115. Pressure detection is performed using terminals 116 and 1.
It is utilized that the potential difference of 17 changes according to the resistance of the pressure conversion element 11.

The amplifier 12 includes COMPs 121 and 122 for comparing signals from the terminals 116 and 117 of the detection section 110 shown in an amplifier circuit diagram 120, and an amplifier 123,
It consists of 124.

The first and second pressure setting units 20 and 30 include D/A converters 21 and 31, and an operational amplifier 2, respectively.
It consists of 2,32. Said D/A converter 2
1 and 31 each have a total of 12 dip switches, and set the first and second reference pressures.

The operational amplifiers 22 and 32 are connected to the D/A
This circuit amplifies the signals input from the converters 21 and 31.

The first and second comparison sections include a comparator 40 and a comparator 40, respectively.
50, that is, it is composed of COMP41, 51.

In this embodiment, in addition to the timer 60, a timer 65 is provided which starts counting time after injection has started.
The time measurement units 60 and 65 have exactly the same configuration,
timer circuits 61 and 66, and signal holding circuit 6, respectively.
It has 2,67. The timer circuits 61 and 66
outputs an H level signal after a predetermined time has elapsed. For control signals, a control circuit 75 that outputs an alarm is provided along with a logic circuit 70. The logic circuit 70 includes an output circuit 71 that outputs a signal from the comparator 40, and a sequence circuit 72 that outputs a control signal to the drive device. in particular,
The logic circuit 70 includes FF71, INV72, OR7
Relay 7 driven by 3, 74, and TR76
7, and the control circuit 75 includes an OR75
1,752, FF753, INV754, and TR
756, and a relay 757 driven by the relay 756.

In this embodiment, an injection start detection unit 80 is provided to detect an injection start signal, and injection is started by a normally open contact 811 of a relay that operates in parallel with a relay that outputs a drive command to the injection cylinder 3. Detect what has happened.

A first reference pressure and a second reference pressure are set in the first and second pressure setting sections 20 and 30 by dip switches, respectively. The molding die 5 is the upper die 7
A cavity 8 is formed using the lower mold 6. The heating cylinder 1 heats the molten resin supplied to the screw 2, and the injection cylinder 3 driven by the drive device 4 starts injecting the molten resin into the cavity 8.

The resistance value of the pressure transducer element 11 of the detector 110 changes depending on the pressure received from the molten resin,
The potentials at terminals 116 and 117 of detector 110 change. The amplifier circuit 120 connects the terminals 116, 117
It amplifies the signal input from the comparator and outputs it to COMP41 and COMP51, which are the first and second comparators. Said
The COMP 41 inputs signals from the amplifier circuit 120 and the first pressure setting section 20, and the signal from the amplifier circuit 120 is input to the first pressure setting section 20.
When the signal exceeds the signal from 0, set the OUT level to H. The COMP 51 performs the same operation as described above.

When the molding pressure increases with the passage of time and reaches the second reference pressure, the OUT level of the COMD51 becomes H, and before the main injection molding cycle starts, a timer set for a predetermined time is activated by a deep switch. The circuits 63 and 68 start counting, and when a predetermined time elapses, the FF71 starts counting.
The level of IN711 becomes H level. Even after the injection is completed, if the molding pressure does not reach the first reference pressure, the level of IN 712 of FF 71 is L, and therefore the level of OUT 713 of FF 71 is L.
However, when the injection is finished, the normally open contact 81
1 becomes open, via TR813 and INV72,
The level of IN712 of FF71 becomes H, therefore the level of OUT713 becomes H, and relay 77 is activated via OR74. In other words, a signal for permission to move from the injection process to the next process is output, and the process moves to the secondary pressurizing process.

When the injection progresses smoothly and the molding pressure exceeds the first reference pressure, the level of the output terminal of COMP41 becomes H, and the control section 70 operates the relay 77 via the OR74, A signal from the normally open contact causes the resin injection molding machine to proceed to the next process.

Even after injection is completed, if the molding pressure does not reach the second reference pressure, the timer unit 68 changes the level of its output terminal to H after a predetermined period of time has elapsed, and the FF
The level of reset terminal 764 of FF753 becomes H, and IN763 of FF753 is L, so OUT
765 becomes L, and relay 7 is activated by INV754.
57 is activated. In other words, a warning lamp indicating a defect in the injection process lights up. When the operator confirms the injection failure and presses the lamp extinguishing button, the opening contact 831 opens and the set terminal 763 of the FF 753 becomes H, and the lamp is extinguished.

According to this embodiment, the conventional control device includes a molding pressure detector, first and second pressure setting sections, and first and second pressure setting sections.
By installing a comparison section, a timing section, an injection start detection section, and a timing section that measures the time from the start of injection, the injection process can be controlled according to the actual pressure condition inside the cavity, and molding defects can be avoided. In addition, when the injection pressure does not rise to a prescribed second reference pressure, a warning lamp can detect an injection failure.

[Effects of the Invention] According to the present invention, the molding pressure detector, the first and second
By arranging the pressure setting section, the first and second comparing sections, and the timing section, the injection process can be controlled according to the actual molding pressure inside the cavity, which means that the occurrence of shots and burrs can be prevented. Waste of molten resin can also be prevented, and the performance of the resin injection molding machine can be improved.

[Brief explanation of the drawing]

FIG. 1 is a pressure-time characteristic diagram showing the pressure inside the cavity of a molding die used to explain the configuration of the apparatus of the present invention. 2 and 3 are block diagrams of specific embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 10... Molding pressure detector, 11... Pressure conversion element, 20... First pressure setting part, 30... Second pressure setting part, 40... First comparison part, 50... Second pressure setting part Comparison section, 60... Timekeeping section, 70... Logic circuit.

Claims (1)

[Scope of Claims] 1. A molding die having a cavity; a heating cylinder for heating molten resin; In a resin injection molding machine comprising a screw for injecting molten resin, an injection cylinder for driving the screw, a drive device for driving the injection cylinder, and a control device for controlling the drive device, the control device a molding pressure detector disposed on the cavity surface of the molding die to detect the molding pressure received from the molten resin injected into the cavity; and a first pressure setting for setting a first reference pressure. a second pressure setting section for setting a second reference pressure smaller than the first reference pressure; a signal from the molding pressure detector and the first pressure setting section; is higher than the first reference pressure, a first comparing section outputs a signal to that effect, inputting signals from the molding pressure detector and the second pressure setting section, and adjusting the molding pressure. a second comparison section that outputs a measurement start signal for measuring elapsed time when the pressure becomes equal to the second reference pressure; and a second comparison section that measures time from the time when the signal is input from the second comparison section. and a timer unit that outputs a signal to that effect after a predetermined time has elapsed, and signals from the first comparison unit and the timer unit, and when either one of the signals is input, stops the injection. , a logic circuit that outputs a control signal to the drive device to maintain the internal pressure in the cavity at the secondary pressure. A resin injection molding machine comprising: