JPH0775454B2 - Power control method for injection molding factory - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the maximum power demand in an injection molding factory having a plurality of injection molding machines.

[Prior Art] Conventionally, in order to reduce the maximum demand power (maximum value of 30 minutes or 1 hour average power in one month) or the amount of power in an injection molding factory, an injection molding machine 1 such as a hydraulic circuit improvement is used. Only reducing the power per stand has been done.

[Problems to be solved by the invention]

However, in recent years, as the number of injection molding machines in the injection molding factory has increased and the factory has become huge, the fluctuation range of the average power (demand power) per hour or 30 minutes of the factory is large depending on the operating status. It has become to. Therefore, if the contract power with the power supply company is set high, the basic charge will be large, and conversely, if the contract power is set low, the additional charge will be levied when the maximum demand power exceeds the contract power. There is a problem.

An object of the present invention is to provide a power control method that reduces the fluctuation range of demand power by leveling the operating conditions of the injection molding machine.

[Means for solving problems]

 First, the principle of power control according to the present invention will be described.

The average electric power X per hour of an injection molding factory (hereinafter referred to as a factory) is divided into the average electric power x of the injection molding machine and the average electric power Δx of other auxiliary equipment. That is, X = x + Δ
x. By the way, the average electric power X of a large-scale factory is dominated by the average electric power x of the injection molding machine, and generally x >> Δx. Therefore, in order to prevent the maximum demand power in one month, that is, the maximum value of the average power X in one month from exceeding the contracted power, the average power x of the injection molding machine that occupies most of the average power X is set to It is necessary to keep it below a certain value.
Therefore, a method of controlling this average power x will be described next.

The number of injection molding machines (hereinafter referred to as machines) M _{1 to MN in} a factory is N, and the molding conditions for each machine Mi (i = 1, ..., N) are predetermined, and accordingly, each machine Mi 1 molding cycle time Ti [sec] and 1 molding sylk power amount wi
It is assumed that [kwh] is fixed. In addition, each machine Mi
Pci [kw] is the average power of the intermediate step (sometimes including a pause step from the completion of one molding cycle to the next cycle, and a molded product take-out step), and the intermediate step time is Tci [se
c], one cycle power consumption Vi (Tci) including the intermediate process of machine Mi and average power per hour ei (Tci)
Are as follows:

The total average power x of all machines is given by the following equation.

Clearly from equation (1), one cycle power consumption Vi (Tc
i) is a monotonically increasing function of the intermediate process time Tci, and normally the average power Pci of the intermediate process is Therefore, from the equation (2), the average power per hour ei
It can be seen that (Tci) is a monotonically decreasing function of the intermediate process time Tci. That is, if the intermediate process time Tci is extended, the machine M
The one-cycle power consumption Vi (Tci) including the intermediate step of i increases, and conversely, the average power ei (Tci) per hour and the total average power x decrease. Therefore, it is more advantageous not to extend the intermediate process time Tci in order to reduce the original unit price of the molded product.
In addition, a so-called trade-off relationship occurs in which it is advantageous to extend the intermediate process time Tci as much as possible in order to reduce the maximum demand power to reduce the contract power, or to keep the contract power within the contract power.

However, it is self-evident that taking only one of the above is less effective. Therefore, within the range where the maximum demand power is kept below the contract power, the intermediate process time Tci that is intentionally set is shortened and the one cycle power consumption Vi
There is a realistic demand for lowering (Tci). Such a requirement can be expressed as the following problem. In other words, Problem I “Set the average power per hour of all the machines you want to set. And under the constraint of 0TciZci, The intermediate process time Tci ^* (i = 1, ..., N) that minimizes is obtained. However, Zci is the maximum extendable intermediate process time allowed in the production plan, and the number of molded products produced by machine Mi (=
Assuming the number of molding cycles) is Ni, and the allowable production time is Ui, Is represented.

Here, if Li = ei (Tci), then from equations (1) and (2) That is, Therefore, this one-cycle power consumption Vi (Tci) becomes a function of the variable Li, and this is designated as Yi (Li). Then, the problem I is mathematically rewritten as follows.

Problem II That is, the problem I of setting the intermediate process time results in the problem II (power distribution problem) of allocating the average power Li to each machine.

Next, an algorithm for solving this problem II will be described. This algorithm is based on the principle of optimality in dynamic programming.
It was derived based on.

First, ai = ei (Zci), far.

_{<STEP1> a 1 <h <} b 1 and _{f 1 (h) = minY 1} (L 1) Distant, f ₁ (h) and f ₁ for each _{a 1 L 1 h h (h} ) = Y 1 Find and store L ₁ ^* that satisfies (L _{1 *} ).

<STEP2> The following sequential calculation is performed from n = 2 to N.

Functional equation Solve for each h that satisfies.

Fn (h) for each h, and Calculate and store L ^* _n .

<STEP3> If h = W and ▲ L ^* _n ▼ and fn (h) are calculated, fn
(H) is the optimum value.

<STEP4> Obtain an optimal solution in the following order from n = N to 2.

By setting h = h- ▲ L ^* _n ▼, ▲ L ^* _n-1 ▼ and fn- ₁ (h) are obtained. Through the above steps, the sequence of optimal solutions (▲ L
^* _n ▼, Ln _{-1 *} , ..., L ^* _n ▼, ..., L ^* _n ▼) are obtained. By the way, from equations (1) and (6) Therefore, using the optimal solution, Then, the intermediate process time ▲ Tc ^* _i ▼ (i = 1 ... N) of each machine Mi is calculated.

0 <▲ Tc ^* _i ▼ <Zci is satisfied, and It is an intermediate process time that satisfies the condition.

The power control method of the injection molding factory of the present invention is based on one molding cycle power amount during operation of each injection molding machine, average power during intermediate steps, and maximum allowable intermediate step time per hour of each injection molding machine. Keep the sum of average power below a predetermined value,
In addition, a plurality of intermediate process times corresponding to each injection molding machine that minimizes the sum of the one-cycle power consumption including the intermediate process of each injection molding machine is calculated, and the plurality of intermediate process times respectively correspond to the injection molding machine. It is characterized by setting to.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention applied to an offline control power control system. Measuring one cycle power amount W ₁ to _W-N of each power meter 1 ₁ to 1 _N injection molding machine M ₁ ~M _N. In the computer 2, the algorithms of STEP1 to STEP4 are stored in advance as a program, and the molding cycle time Ti of the injection molding machine Mi (i = 1, ..., N), the intermediate process average power Pci, and the maximum extendable intermediate process time. Each value of Zci and the average electric power W per hour of all injection molding machines is preset internally, and when one cycle electric energy Wi is input, the intermediate process time Tci is calculated based on this algorithm.

Next, the operation of the embodiment of the present invention will be described.

First, one cycle power amount W ₁ to _W-N of the power meter 1 ₁ to 1 by the _N connexion injection molding machine M ₁ ~M _N are measured, respectively. Then, one cycle power amount W ₁ to _W-N from the input device is the measurement value of the power meter 1 ₁ to 1 _N by an operator (not shown) is input to the computer 2, is further program execution, each of the computer 2 The intermediate process time Tci of the injection molding machine Mi is output. These intermediate process times Tci are set by the operator in a controller (not shown) of each injection molding machine Mi.

FIG. 2 shows a second embodiment applied to an online control power control system. Wattmeter 1 ₁ to 1 _N may be respectively measured cycle power amount W ₁ to _W-N and intermediate steps average power Pci~Pcn of the injection molding machine M ₁ ~M _N output. MODEM3 _{1 to} 3 _N is one cycle electric energy W _{1 to} W _N and intermediate process average power Pci to P
Digitize cn. MODEM4 sequentially connects the respective outputs of MODEM3 _{1 to} 3 _{N to} the computer 5. The computer 5 stores the above-mentioned STEP1 to 4 algorithms as a program in advance, and the injection cycle Mi of the injection molding machine Mi, Ti,
The maximum extendable intermediate process time Zci and the average electric power W per hour of all injection molding machines are preset internally, and 1 cycle electric energy Wi and intermediate process average electric power Pc _{1 to} Pc
When c _N is input, the intermediate process time Tci is calculated based on this algorithm.

In this case, one cycle power measured by the power meter 1i
Wi is input to the computer 5 via MODEM 3i, 4 and the intermediate process time Tci calculated by the computer 5 is automatically set in a control device (not shown) of the injection molding machine Mi.

〔The invention's effect〕

As described above, according to the present invention, the maximum demand power is kept below a predetermined value (contracted power) and the sum of the one cycle power consumption including the intermediate process of each injection molding machine is minimized. The process time is calculated and set in each injection molding machine.

As a result, the demand power of the factory can be controlled according to the contracted power determined by the injection molding factory. That is, since the demand power can be controlled so as not to exceed the contracted power, the surcharge can be avoided. Further, when the contracted electric power is set, the contracted electric power can be kept low, so that the basic charge can be lowered. From the above, it is possible to reduce and reduce the waste of electric power cost in the injection molding factory, and it is possible to expect a great economic effect.

In addition, the operating conditions of the factory will be leveled and the idle time of the equipment will be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention applied to an offline control power control system, and FIG. 2 is a block diagram of another embodiment applied to an online control power control system. 1 ₁ to 1 _N ...... Power meter 2,5 ...... Computer 3 _{1 to} 3 _N , 4 ...... MODEM M _{1 to MN} ...... Injection molding machine Tc _{1 to} Tc _N ...... Intermediate process time

Claims (1)

[Claims] 1. In an injection molding factory having a plurality of injection molding machines, each injection molding is performed from one molding cycle electric power amount during operation of each injection molding machine, average power during intermediate process, and maximum allowable intermediate process time. A plurality of intermediates corresponding to each injection molding machine that keeps the sum of average electric power per hour of the machine below a predetermined value and minimizes the sum of power consumption of one cycle including the intermediate process of each injection molding machine. An electric power control method for an injection molding factory, comprising calculating a process time and setting the plurality of intermediate process times in respective corresponding injection molding machines.