JPH02239916A - Temperature control method for heating cylinder of molding machine - Google Patents

Abstract

PURPOSE:To prevent lowering of temperature of a heating cylinder and shorten the starting time of a molding machine by estimating the amount of heat taken from a heating cylinder at the time of mold starting of the molding machine and supplying the amount of heat consisting of said estimated heat and the operation heat amount to the heating cylinder. CONSTITUTION:An input generator 16 is incorporated in parallel with a PID controller 13, and responds to a synchronization and output delay signal from the PID controller 13 and outputs an additional control signal Ua responding to the amount of heat gamma to be taken out of a heating cylinder 10. Said additional control signal Ua is added to a control signal Uo from the PID controller 13 by means of an adding machine 17, and said added control signal is added to a heater 14. The temperature lowering of the heating cylinder 10 at the time of starting lowering is controlled by said arrangement to shorten the starting time of the molding machine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the temperature of a heating cylinder of a molding machine.

[Conventional technology]

Conventionally, temperature control of a heating cylinder of a molding machine such as an injection molding machine is performed as shown in FIG. The temperature θ0 of the heating cylinder 10 is detected by a thermocouple 11. Subtractor 1
In step 2, the heating cylinder temperature θ0 detected by the thermocouple 11 is subtracted from the set temperature θr to obtain the deviation e=θr−θ0.

In response to this deviation e, the PID controller 13 controls the heater 14 for heating the heating cylinder 10 on and off using the control signal Uo, as shown in FIG. The operating heat amount Qm is supplied to 10.

[Problem to be solved by the invention]

By the way, as is well known, when the injection molding machine starts molding, resin whose temperature is lower than that of the hopper is supplied into the heating cylinder 10. Therefore, a large amount of heat is taken away from the heating cylinder 10, and the temperature of the heating cylinder 10, particularly the portion of the heating cylinder near the water-cooled cylinder, drops rapidly, as shown by the solid line in FIG. In FIG. 4, the amount of heat taken away is shown as a disturbance γ applied to the adder 15 between the heater 14 and the heating cylinder 10. Therefore, there is a drawback that it takes a considerable amount of time to return the temperature of the heating cylinder 10 to the set temperature θO before molding.

An object of the present invention is to provide a method for controlling the temperature of a heating cylinder of a molding machine, which can prevent the temperature of the heating cylinder from decreasing at the start of molding and shorten the start-up time of the molding machine.

[Means to solve the problem]

A method for controlling the temperature of a heating cylinder of a molding machine according to the present invention includes:
In a temperature control method, the temperature of a heating cylinder of a molding machine is controlled by adding to the heating cylinder an operating amount of heat corresponding to the difference between a set temperature and a detected temperature of the heating cylinder. When the machine starts molding, the amount of heat that will be taken away from the heating cylinder is predicted in advance, the predicted amount of heat is added to the amount of operation heat, and the added amount of heat is supplied to the heating cylinder.

[For production]

When the molding machine starts molding, the amount of heat that will be taken away from the heating cylinder is predicted in advance, this predicted amount of heat is added to the operating amount of heat, and this added amount of heat is supplied to the heating cylinder, so the temperature of the heating cylinder decreases. can be suppressed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, a heating cylinder temperature control device to which a temperature control method according to an embodiment of the present invention is applied is shown in FIG. 4 except that an input generator 16 and an adder 17 are added. It has the same configuration as the one above.

The input generator 16 is incorporated in parallel with the PID controller 13 and responds to the synchronization and output delay signals from the PID controller 13 to generate an additional control signal Ua (third The diagonally shaded area in the figure) is output. This additional control signal Ua is sent to the PID controller 1 by the adder 17.
3 (white portion in FIG. 3) and this added control signal is applied to the heater 14.

As a result, in the conventional temperature control method, the temperature of the heating cylinder 10 decreased at the start of molding, as shown by the solid line in FIG. As shown by the broken line, the temperature drop of the heating cylinder 10 at the start of molding can be suppressed. Therefore, the start-up time of the molding machine can be shortened.

Hereinafter, a method for determining the additional control signal Ua output from the input generator 16 will be specifically explained.

In FIG. 2, the shaded area represents the amount of heat Q+ [Cal/m2
It is Ko. This amount of heat q1 is expressed by the following formula.

Here, i+ is the time [H] when the temperature of the heating cylinder 10 starts to decrease from the steady state, and t2 is the time when the temperature of the heating cylinder 1
The time [H] when the temperature of 0 returns to the steady state, ρ is the specific weight of the heating cylinder 10 [1c g f/m3],
C is the specific heat of the heating cylinder 10, ■ is the volume of the heating cylinder 10 [m3], θr is the temperature (set temperature) of the heating cylinder 10 in a steady state [°C], and θ(1) is the temperature of the heating cylinder 10 at time t. ['C] and dt each represent minute time.

Next, the heat radiation ffiq2 [Cal/m2] per unit area from the surface of the heating cylinder 10 is expressed by the following formula.

Here, α is the heat transfer coefficient of the surface of the heater 14 [W/m2°C
K, θ flash is the ambient temperature [°C].

Therefore, from equations (1) and (2), the amount of heat γ in the shaded area in FIG. 2 can be determined by the following equation.

γ”'ql+Q2 (3) Therefore,
The heat mQ to be heated by the heater 14 is expressed by the following formula.

Q=Sγ (4) Here, S
is the heating area [m2] of heater]4.

Therefore, if the capacity of the heater 14 is A [W'l,
The heating time T1 of the heater 14 is expressed by the following equation.

T-=Q/A (5) As described above, the heating time T' of the heater 14 is determined in advance through experiments, and the heater 14 is continuously heated for the time T'.

However, in reality, since the heater 14 generally has only one operating point, the control signal UO output from the PID controller 13 and the A-1 addition control signal Ua output from the human power generator 16 are independently controlled. It is not possible to simultaneously apply this to the heater 14. Therefore, the following method is adopted.

That is, the control signal Uo from the PID controller 13
and the additional control signal Ua from the input generator 16 are divided and superimposed, and the output is applied to a relay (not shown). The number of divisions X at this time is from time t1 to time t
Assuming that up to 2 are equally divided and the period of the PID controller 13 is T, it is expressed by the following equation.

X = (t 2 t 1) / T one time PID
During the period T of the controller 13, the input generator 1
Output time Δt for superimposing the additional control signal Ua from 6
is expressed by the following formula.

Δt-T-/X By the way, in this embodiment, a frequency oscillator is used as the input generator 16, and the output level, period T1, and output time 8T are adjusted and used.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, by maintaining the temperature of the heating cylinder substantially constant before and after molding, the start-up time of the molding machine can be shortened.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a heating cylinder temperature control device of a molding machine to which a temperature control method according to an embodiment of the present invention is applied, and Fig. 2 shows the temperature of a heating cylinder according to the conventional temperature control method and the temperature control method of the present invention. FIG. 3 is a time chart showing an example of the control signal applied to the heater by the temperature control method of the present invention. FIG. 4 is a heating cylinder of a molding machine to which the conventional temperature control method is applied. FIG. 5 is a block diagram showing the configuration of the temperature control device, and a time chart showing an example of a control signal applied to the heater by a conventional temperature control method.

Claims (1)

[Claims] 1. In a temperature control method for controlling the temperature of a heating cylinder of a molding machine by adding to the heating cylinder an operating amount of heat corresponding to the difference between the set temperature and the detected temperature of the heating cylinder, The method is characterized in that the amount of heat that will be removed from the heating cylinder is predicted in advance when the molding machine starts molding, the predicted amount of heat is added to the amount of operation heat, and the added amount of heat is supplied to the heating cylinder. Temperature control method for heating cylinder of molding machine.