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
Reexamination Certificate
2001-08-10
2004-01-13
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
C318S801000, C318S812000, C425S149000, C425S150000
Reexamination Certificate
active
06676400
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control unit of a motor for an injection molding machine, in particular, to a control unit for controlling a servo motor used for a motor-driven injection molding machine or a hybrid molding machine.
2. Description of the Related Art
Drive methods of an injection molding machine are broadly classified into hydraulic and motor drive methods. While previously the hydraulic method had been mainly used, the motor drive method has now become more common. This is attributable to features of the motor drive method including a high rigidity of the power transmission mechanism, good ability to control position and speed of the movable parts, and a high energy conversion efficiency. However, the hydraulic method has a feature permitting easy and accurate force control of the driving section, that is unavailable in the motor drive method. A hybrid method has therefore been developed which combines the motor and the hydraulic drive methods.
FIG. 1
illustrates the configuration of a typical motor-driven injection molding machine. This motor-driven injection molding machine has an injection unit
10
and a mold clamping mechanism
20
. The injection unit
10
comprises a hopper
11
for temporarily storing a raw resin material, a heating cylinder
12
for plasticizing and melting a resin fed from the hopper
11
, and a screw
13
for metering the molten resin in the heating cylinder
12
and injecting the thus metered molten resin. The molten resin is injected into a cavity positioned between a fixed mold
21
and a movable mold
22
.
The mold clamping mechanism
20
comprises the fixed mold
21
, the movable mold
22
, a fixed platen
23
and a movable platen
24
, to which the fixed mold
21
and the movable mold
22
are attached, respectively, a toggle link
25
for moving the movable platen
24
, and a plurality of tie bars
26
for guiding the movable platen
24
.
The motor-driven injection molding machine further comprises a plurality of drive motors (servo motors). The plurality of drive motors includes an injection motor
14
to move the screw forward and backward; a metering motor
15
for rotating the screw
13
; an injection unit moving motor
16
to move the entire injection unit
10
forward and backward; a mold opening/closing motor
27
for moving the movable platen
24
; an ejecting motor
29
to move an eject pin
28
incorporated in the movable platen
24
forward and backward; and a mold thickness complying motor
30
to move the movable platen
24
and the toggle link
25
in accordance with the thickness of the fixed mold
21
and the movable mold
22
.
The plurality of drive motors
14
to
16
,
27
,
29
and
30
are individually drive-controlled. For example, when all the drive motors are three-phase motors, as shown in
FIG. 2
, a servo controller
41
is connected via a three-phase inverter
40
to each of the drive motors
14
to
16
,
27
,
29
and
30
. An encoder
42
for detecting rotation of the motors and two current sensors
43
for detecting the magnitude of drive current fed from the three-phase inverter
40
are attached to each of the drive motors
14
to
16
,
27
,
29
and
30
. Detection signals from the encoder
42
and the current sensors
43
are fed back to the servo controller
41
.
The servo controller
41
issues, under control of an upper control unit not shown, a control signal to the three-phase inverter
40
on the basis of the detection signals fed back from the encoder
42
and the current sensors
43
. The three-phase inverter
40
generates signals (drive current) for three phases including U-phase, V-phase and W-phase in response to the control signal from the servo controller
41
, and feeds the same to the three-phase motors. The three-phase motors thus rotate by an instructed amount of rotation at a timing instructed by the upper control unit.
In the motor-driven injection molding machine, as described above, the drive motors
14
to
16
,
27
,
29
and
30
are independently controlled by the corresponding servo controllers, and injection molding is thus carried out.
A hydraulic injection molding machine is characterized in that it is possible to achieve a larger transmission energy per unit time with a relatively small-sized apparatus. This is why there is a tendency toward adopting the hydraulic method for a large-scale (large-output) injection molding machine. There is, however, a demand for adopting the motor drive method or the hybrid method also for a large-capacity injection molding machine.
In order to adopt the motor drive method or the hybrid method for a large-capacity injection molding machine, it is necessary to provide a large-output motor. In order to control the large-output motor, it is necessary to increase the maximum dielectric strength or maximum current of the inverter. Along with this, the corresponding voltage must be increased, for example, from 200-V class to 400-V class, for the control system of the servo controllers or the like.
On the other hand, the maximum output torque of the motor required for the injection molding machine varies with the drive source. For example, there is a considerable difference between the maximum output torque that the mold opening/closing motor is required to have and the maximum output torque that the ejecting motor is required to have. Even within a molding cycle, the torque that a motor is required to have is not constant. A large torque is required in some cases, and only a small torque suffices in others. When adopting the motor drive method or the like for a large-capacity injection molding machine, therefore, it is necessary to provide motors, inverters and servo controllers in response to the maximum output torque and change in torque necessary for the individual driving sources. This presents a problem in that the individual motors cannot have a common control unit.
Japanese Unexamined Patent Application Publication No. 2000-41392 (hereinafter referred to as “Publication 1”) discloses a brushless DC motor comprising an inverter connected to two three-phase windings. Japanese Unexamined Patent Application Publication No. 7-298685 (hereinafter referred to as “Publication 2”) discloses an invention that can drive a six-phase induction motor by the use of two inverters. However, because the two inverters are connected to the same controller, it is necessary to change the configuration (software) of the controller in accordance with the purpose of use in the above-mentioned Publications 1 and 2. The inventions disclosed in Publications 1 and 2 suggest nothing about the following object of the present invention of a common control unit, and disclose or suggest nothing about means for achieving such an object.
Furthermore, in the conventional motor-driven type injection molding machine or hybrid molding machine, a single drive motor is connected to a single inverter, and a single servo controller is connected to this inverter. When the inverter fails and cannot be controlled by the servo controller, runaway of the drive motor may occur. If such a runaway occurs, for example, in the mold opening/closing motor
27
, the movable mold
22
held by the movable platen
24
collides with the fixed mold
21
held by the fixed platen
23
, thus leading to breakage of these molds.
In the control unit of the motor for the conventional injection molding machine, as described above, if an inverter fails and the motor is in a runaway state, a problem exists in that there are no means for stopping the motor. For example, the brushless DC motor disclosed in Publication 1 has an object to rotate the motor even when a problem occurs in an inverter circuit or the like. Publication 1 does not disclose or suggest anything about stopping a runaway motor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to make it possible to concurrently use various portions of a control unit for controlling drive motors used in an injection molding machine. In other words, the present
Heitbrink Tim
Nokia Corporation
Squire Sanders & Dempsey L.L.P.
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