Intelligent hydraulic manifold used in an injection molding...

Details Intelligent hydraulic manifold used in an injection molding... Intelligent hydraulic manifold used in an injection molding...

1998-10-16

2001-09-11

Grant, William (Department: 2121)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S019000, C700S028000, C700S054000, C700S200000, C425S145000, C425S149000

Reexamination Certificate

active

06289259

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and methods for controlling a hydraulic actuator for use in an injection molding machine, and more particularly to controlling such a hydraulic actuator (both linear and rotary) with a processor which is disposed locally near the actuator and/or the hydraulic manifold.
2. Related Art
Injection molding machines produce great quantities of products at high speed. For example, the widely-used PET plastic drink containers are made at production rates of thousands per hour. During these high speed operations, various injection molding machine devices (such as the molding clamp assembly, the injectors, various control switches, and other machine components) are moved using a number of hydraulic actuators. Such hydraulic actuators are supplied with pressurized hydraulic fluid that causes movement of an internal diaphragm or piston which, in turn, drives the molding device. A control valve controls the flow of hydraulic fluid to the actuator to control movement of the diaphragm.
FIG. 1
depicts a typical control valve. In
FIG. 1
, the hydraulic actuator
2
includes a piston
4
which divides a chamber into two halves
6
and
8
. Movement of the piston
4
drives a load
10
, which, for example, may comprise a mold and clamp mechanism. A position sensor
12
senses the position of the load
10
and provides a feedback signal to a system controller (to be discussed below).
The hydraulic actuator
2
has two hydraulic fluid lines
64
and
84
which allow hydraulic fluid to enter and escape from the chamber halves
6
and
8
, respectively. Pressure transducers
66
and
86
respectively monitor the pressure in line
64
and
84
and provide output signals to the system controller.
Hydraulic fluid from a pressure source (typically a hydraulic fluid pump; not shown in
FIG. 1
) is provided to valve
14
through hydraulic line
74
, while hydraulic fluid may be returned from valve
14
to hydraulic fluid storage tank (also not shown in
FIG. 1
) through hydraulic line
94
. Pressure transducers
76
and
96
respectively monitor the pressure in lines
74
and
94
and provide output signals to the system controller.
Valve
14
controls the flow of hydraulic fluid through the chambers of hydraulic actuator
2
to move the piston
4
back and forth thus driving the load
10
. Valve
14
has fluid ports A, B, P, and T which are respectively coupled to the hydraulic lines
64
,
84
,
74
, and
94
, as shown. The valve
14
has a straight flow section
142
and a cross-flow section
144
which are respectively driven by solenoids
146
and
148
in order to control the flow of fluid within the valve. For example, when the straight flow section
142
is driven to the A, B, P, and T ports, pressurized fluid will flow through lines
74
and
64
into chamber
6
, driving the piston
4
toward the load
10
. On the other hand, if cross-flow section
144
is driven to the ports A, B, P, and T, then pressurized hydraulic fluid will be provided through lines
74
and
84
to the chamber
8
, driving the piston
4
away from the load
10
.
In the related art, control of the hydraulic actuator
2
through the valve
14
was a relatively straightforward process. For example, U.S. Pat. No. 5,062,052 (incorporated herein by reference) discloses that such actuators may be controlled with an analog signal processor and/or a programmable logic controller which are disposed at a location remote from the injection molding actuators so that the processing circuitry is not damaged by machine heat and vibration. Typically, the analog signal processor and/or the programmable logic controller will perform closed-loop control of the actuator
2
through valve
14
in order to keep load
10
moving within the prescribed operational ranges. The analog signal processor and/or programmable logic controller will receive feedback signals from the pressure transducer units
66
,
76
,
86
, and
96
, and position information from position sensor
12
in order to control valve
14
according to a predetermined control program. The analog signal processor can also effect operational changes in the operation of the actuator
2
through command signals received through the programmable logic controller, for example to change the molding and clamping times used by load
10
.
The programmable logic controller stores a plurality of predetermined control programs which cause the analog signal processor to control the analog devices of the injection molding machine. The programmable logic controller may also include circuitry for controlling the digital devices in the injection molding machine, for example, digital solenoid valves and proximity switches. The programmable logic controller thus controls the elements of the injection molding machine either through the analog signal processor or directly through the digital devices.
In the control scheme of the '052 Patent, however, the analog signal processor and the programmable logic controller are required to perform command and control operations for all of the various devices in the machine. This imposes a processing bottleneck. For example, the programmable logic controller may attempt to execute closed-loop control of multiple different analog devices at the same time. Typically, faster and more powerful processors have been used in an attempt to overcome such problems. Such expensive solutions have, nevertheless, been unable to solve the control timing problems experienced in known actuator control architectures.
Another problem with the known control architecture is the reliability of the analog signal processor and the programmable logic controller. If either one of these components fails, the entire machine must be stopped until a replacement is located, installed, and programmed to operate in the specified machine. Since each actuator in every machine has unique operating characteristics, the newly-installed processor(s) must be re-programed and/or re-parameterized with the operating characteristics of the corresponding actuator(s) before full-scale production can be resumed.
Furthermore, the dedicated wiring inter-connections used for communication between the analog signal processor and the programmable logic controller to each actuator results in a plurality of wires which are difficult to install, maintain, and repair.
Thus, a need exists for a control architecture for hydraulic actuators in an injection molding machine which provides fast, flexible, and reliable control of the actuators.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the problems noted above by providing a local processor disposed near the actuator so that control functions are moved closer to the actuator and away from the central processor. Preferably, a microcontroller is mounted directly on each hydraulic fluid distribution manifold, and this microcontroller controls the actuators coupled to that manifold. Each hydraulic actuator can be controlled from a local processor, eliminating the need for a great number of wires between the actuator and the analog signal processor and/or the machine controller, such as a programmable logic controller. This enables modular control sub-systems to be realized. Also, a failure of any manifold-mounted microcontroller will only require its replacement, not the replacement of the central controller or the other manifold microcontrollers.
According to a first aspect of the present invention an intelligent hydraulic actuator for use in an injection molding machine which also has a system controller includes a hydraulic actuator for moving in a linear or rotary manner between first and second positions ,or for generating forces or torque in response to hydraulic flow and pressure, respectively. A microcontroller is disposed adjacent the actuator for causing the actuator to move between the first and second positions. The microcontroller is also coupled to the system controller.
According to another aspect of the present invention,

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