Hydraulic circuit of an injection molding machine

Details Hydraulic circuit of an injection molding machine Hydraulic circuit of an injection molding machine

2000-01-21

2001-07-10

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Control means responsive to or actuated by means sensing or...

Feed control of material en route to shaping area

C425S149000

Reexamination Certificate

active

06257859

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic circuit of an injection molding machine having a differential mode in which drain oil ejected from an injection cylinder during injection is utilized as working fluid.
2. Description of the Relevant Art
Japanese Patent Application Laid-Open (kokai) No. 6 (1994)-246800 discloses a conventional hydraulic circuit of an injection molding machine which permits selection of either a regular mode or a differential mode. In the regular mode, all drain oil ejected from a front oil chamber of an injection cylinder during injection is returned to an oil tank. In the differential mode, all or a portion of drain oil is supplied to a rear oil chamber of the injection cylinder.
FIG. 4
schematically shows a simplified block diagram of a conventional hydraulic circuit
50
for the purpose of illustrating the principle of the hydraulic circuit
50
.
In
FIG. 4
, when a mode selector valve
51
is changed over to a right-side position marked with symbol R (hereinafter referred to as the R position), the regular mode is established. Working fluid discharged from a hydraulic power unit
52
during injection is supplied via a main circuit
53
to a rear oil chamber
61
r
of an injection cylinder
61
of an injection molding machine
60
. All drain oil ejected from a front oil chamber
61
f
is returned to an oil tank
54
via the mode selector valve
51
set in the R position and the main circuit
53
.
When the mode selector valve
51
is changed over to a left-side position marked with symbol L (hereinafter referred to as the L position), a differential mode is established. Working fluid discharged from the hydraulic power unit
52
during injection is supplied to the rear oil chamber
61
r
of the injection cylinder
61
via the main circuit
53
. Drain oil ejected from the front oil chamber
61
f
flows through the mode selector valve
51
set in the L position and merges with working fluid from the main circuit
53
. The resultant mixture is supplied to the rear oil chamber
61
r
of the injection cylinder
61
. In the differential mode, drain oil ejected from the injection cylinder
61
is utilized as working fluid without being returned to the oil tank
54
, thereby enabling injection at a relatively high flow rate of working fluid without an increase in the amount of working fluid supplied from the hydraulic power unit
52
, and thus implementing an increase in injection speed, a reduction in the size of an oil line, and prevention of impact pressure.
However, in spite of yielding of the above advantages through selection of the differential mode, the hydraulic circuit
50
having the differential mode yields the following disadvantage. Even when the supply of working fluid from the main circuit
53
is stopped, drain oil ejected from the front oil chamber
61
f
circulates directly to the rear oil chamber
61
r
due to inertia of a piston of the injection cylinder
61
. As a result, at the time of stoppage of injection, braking control cannot be performed precisely and accurately. For precise, accurate braking, the conventional hydraulic circuit requires an additional braking circuit, resulting in an increase in the number of components of the hydraulic circuit and an associated increase in manufacturing cost. Also, control becomes complicated and unstable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hydraulic circuit of an injection molding machine capable of eliminating or simplifying an additional braking circuit to thereby reduce the number of components and manufacturing cost thereof and capable of facilitating and stabilizing control.
Another object of the present invention is to provide a hydraulic circuit of an injection molding machine capable of performing precise, accurate braking control to thereby drastically improve molding quality.
To achieve the above objects, the present invention provides a hydraulic circuit of an injection molding machine permitting selection of either a regular mode, in which all drain oil ejected from a front oil chamber of an injection cylinder during injection is returned to an oil tank, or a differential mode, in which all or a portion of the drain oil is supplied to a rear oil chamber of the injection cylinder during injection. The hydraulic circuit comprises a 4-port servo valve having A, B, P, and T ports and adapted to drive and control the injection cylinder; a shutoff valve for selecting the regular mode or the differential mode; and a logic valve. The A and B ports of the servo valve are connected to the front oil chamber and the rear oil chamber, respectively, of the injection cylinder. The P port of the servo valve is connected to a hydraulic power unit. The T port of the servo valve is connected to the oil tank via the shutoff valve. The T port is also connected to the rear oil chamber of the injection cylinder via the logic valve.
When the shutoff valve is opened, the regular mode is established, so that the T port of the servo valve communicates with the oil tank via the shutoff valve. During injection in the regular mode, working fluid from the hydraulic power unit is supplied to the rear oil chamber of the injection cylinder of the injection molding machine via the servo valve. All drain oil ejected from the front oil chamber of the injection cylinder is returned to the oil tank via the shutoff valve. When the shutoff valve is closed, the differential mode is established. During injection in the differential mode, working fluid from the hydraulic power unit is supplied to the rear oil chamber of the injection cylinder via the servo valve. Drain oil ejected from the front oil chamber flows through the logic valve and then merges with working fluid from the hydraulic power unit. The resultant mixture is supplied to the rear oil chamber of the injection cylinder. At the time of stoppage of injection, a regular injection stoppage is performed by means of the servo valve. Since drain oil ejected from the front oil chamber of the injection cylinder is supplied to the rear oil chamber via the servo valve, which constitutes a meter-out circuit, the servo valve serves also as a braking circuit.
The present invention further provides a hydraulic circuit of an injection molding machine permitting selection of either a regular mode, in which all drain oil ejected from a front oil chamber of an injection cylinder during injection is returned to an oil tank, or a differential mode, in which all or a portion of the drain oil is supplied to a rear oil chamber of the injection cylinder during injection. The hydraulic circuit comprises a servo valve, a shutoff valve, and a logic valve. The rear oil chamber of the injection cylinder is connected to a hydraulic power unit side via the servo valve. The front oil chamber of the injection cylinder is connected to the oil tank via the shutoff valve. The front oil chamber is connected to a P port of the servo valve via the logic valve.
In the regular mode, the shutoff valve is opened, so that the front oil chamber of the injection cylinder communicates with the oil tank via the shutoff valve, and a selector circuit is changed over so as to close the logic vale. Accordingly, during injection, working fluid from the hydraulic power unit is supplied to the rear oil chamber of the injection cylinder via the servo valve, and all drain oil ejected from the front oil chamber is returned to the oil tank. In the differential mode, the shutoff valve is closed, and the selector circuit is changed over so as to permit opening of the logic valve. Accordingly, during injection, working fluid from the hydraulic power unit is supplied to the rear oil chamber of the injection cylinder via the servo valve. Drain oil ejected from the front oil chamber flows through the logic valve and then merges with working fluid from the hydraulic power unit. The resultant mixture is supplied to the rear oil chamber of the injection cylinder via the servo valve. At the time of stoppage of injection, a regular i

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