Injection Mold Data Transmission System

The present invention relates to injection molding apparatus and procedures and more particularly to a structure and method for enabling and facilitating the transmission of information from injection mold sensors to a control device without the use of cumbersome and expensive analog hard-wired connections. The present invention also provides increased reliability in the feedback control loop as it enables the user to eliminate numerous junctions which can introduce errors into the control system.

Injection molding is typically done in molds which operate at high temperatures and high pressures within the molds. Typical molds include means to heat the molds at numerous points within the mold in order to ensure that the material injected into the mold remains in a molten state until the mold cavity is completely filled and that no voids exist within the cavity (i.e. hot runner system) as is known to those skilled in the art. In addition, as is known to those skilled in the art, it can be desirable to heat a mold, prior to injecting material therein, in order to control the rate at which the material cools and hardens in order to effect the material properties of the molded product (e.g. material strength, etc.)

In order to effect such control, it is necessary to provide a closed-loop feedback system between the controlled device (e.g., a mold heater) and the mold sensor (e.g., a mold temperature sensor), through a controller of some sort which can utilize the information from the mold sensor and control the controlled device in accordance with a predetermined set of instructions. Currently, information from injection mold sensors is transmitted to a controller in analog form via a hard-wired connection which utilizes sensor specific wires which are physically connected to the sensors and the control device through a series of connectors. These wires, used with readily available connectors, create sensor feedback cables. Each cable typically requires two or more wires per sensor located in the mold to transfer an analog signal.

The number of cables required to transfer the information as applied to, for example, temperature in thermal analog form, from the mold to the control device, is dependent on the number of sensor devices located in the mold, but often times exceeds 48 wires for a typical commercial mold configuration. For example, if a mold requires 30 sensor devices, 60 analog sensor wires would typically be required. In addition, each of the sensor wires is typically arranged such that there are 7 thermal junction points between the sensor device and the control device for each sensor wire. Accordingly, in an injection mold such as the one described above, there would be 420 connections created between the sensor devices in the identified mold and the control device for that mold.

Closed-loop feedback systems such as those described above with numerous wires and connectors can create various problems known to those skilled in the art, including: 1) problems associated with bad connections and cold solder joints which may feedback faulty or intermittent data; 2) inaccurate feedback due to temperature variations along the path of the analog feedback cable; 3) the effects of electrical noise on low level analog signals over the span of the feedback cable; 4) numerous problems caused by the sheer volume of cables and wires required, including problems as simple as storage of the wires and cables, and people tripping over cables located on the floor of the injection mold area; and 5) other problems known to those skilled in the art. As the number of sensors in a given mold increases, so too does the number of wires and connections in a conventional system. Thus, as the mold becomes more intricate or sophisticated and control of the operation of the mold becomes more critical, the chance for induced error in a conventional control system similarly increases. Indeed, one practical limitation on the number of temperature sensors which can be effectively employed in injection molding systems results from the limitation on the number of sensor and control wires which a system and system operator can manage.

The preferred embodiment of the present invention provides for sensor input circuitry to be positioned within a thermally isolated enclosure attached to the mold or positioned in the vicinity of the mold. A signal processor, which in the preferred embodiment of the present invention converts analog sensor signals from the sensors into a digital format is also provided. In addition, the present invention includes a communicator positioned within the thermally isolated enclosure to transmit information from the mold temperature sensors, once it has been converted to digital format, to the mold controller and a receiver positioned in or in the proximity of the mold controller to receive said digital information transmitted to the mold controller from the communicator so as to permit the closed-loop control of the molding apparatus.

The advantage of the invention is that, unlike the system of the prior art which required numerous analog connections and the concomitant problems associated therewith, the present invention allows the transmission of signals from the. sensor input circuitry to the mold controller to be accomplished by digital means, thereby eliminating numerous analog connections and the associated problems therewith. This digital interface eliminates all but one of the analog connections, thereby almost entirely eliminating the possibility of junction induced error. In addition, because the information is preferably converted to digital form within a thermally isolated enclosure located on the proximity of the mold itself and transmitted in such form to the control device, the possibility of electrical noise effecting an analog control signal is also greatly reduced. Furthermore, many advantages are created through the elimination of the numerous cables required by the prior art, including: 1) reduced replacement costs for the numerous wires; 2) reduction in cable connection errors; 3) energy and space savings due to the elimination of the need to transport and store the vast number of wires and cables required under the prior art; 4) elimination of the safety hazard created when low level analog signals run next to high power output cables, which may be mistakenly connected to the wrong device and cause damage, fire or electrocution; and 5) elimination of the safety hazard created when numerous wires and cables are run along the floor of the area in which the injection mold is positioned.

The present invention will be described more fully in reference to the accompanying drawings, wherein:

FIG. 1 is an illustrative prospective view of a typical mold and associated control device utilizing a system of the prior art;

FIG. 2 is a schematic block diagram of the preferred embodiment of the system of the present invention; and,

FIG. 3 is an illustrative prospective view of a typical mold and associated control device utilizing a system incorporating the present invention.

As is illustrated in FIG. 1, the system of the prior art provides for an injection molding system 1 to have a number of wires 2 running from the mold 1 to the mold controller 3. These wires carry analog information from the mold to the controller and commands or switched electrical power from the controller to the controlled elements associated with the mold. The mold controller must be located away from the mold due to its physical size and due to the environment in which a mold operates, namely an environment in which the mechanical operation of the mold/machine requires it to be suitably secure from any human contact during operations associated with typical injection molding processes. The controlled elements associated with the mold can be mold heaters arranged to heat the mold or the material injected therein (i.e., thermal elements), or valve pistons or the like arranged to create positive opening and closing of the gate within the mold for use in the injection molding process as known to those skilled in the art (i.e., valve gates) and mold/material pressure sensing devices known as cavity pressure sensors.

As is illustrated in FIG. 3, the system of the present invention includes: 1) a mold 1; and 2) a mold controller for receiving and processing information received from the mold as well as for generating control signals for transmission to one or more controlled elements associated with the mold. Sensors 3 are placed at desired locations on, in or around the mold. Such sensors can be directed to sensing information about the temperature, the pressure, the flow or any other variable which the operator wishes to monitor or measure. A temperature sensor input device typically consists of a bi-metallic thermocouple of the type known in the art which generates an analog signal from which a temperature can be determined. Similar sensor elements relating to pressure and other variables are known to those skilled in the art.

In the preferred embodiment of the present invention, the thermally isolated enclosure 4 is coupled 5 to the mold or to a holding structure in the vicinity of the mold. The thermally isolated enclosure can be constructed from a plastic or metallic material with a thermally nontransmissive material attached between the enclosure and the mold itself.

Arranged within the thermal enclosure are a junction box 6 which houses the interface connections between the mold sensors and the IMDT thermal enclosure. The IMDT thermal enclosure houses electrical and electronic components that include, a signal processor, a transmitter and a power supply. The junction box is arranged to provide a place to simply connect the wires from the mold sensor devices to the IMDT device. The junction box is detachable from the thermal enclosure to facilitate quick replacement of faulty components.

As illustrated in FIG. 2, the signal processor of the preferred embodiment includes a sensor conditioning input circuit, an isolation circuit 1, a multiplexer 3, an amplifier 4, a microprocessor 6, and an analog to digital converter 5 as well as the closed loop return logic from the control device. The sensor conditioning input circuit 1 is connected to the IMDT input devices 7, and serves to amplify the signals and filter noise from the analog inputs. The isolation circuit 2 is connected between the micro-processor 6 and the analog digital converter 5, the isolation circuit acts to optically isolate the signal conditioning and conversion circuitry from the logic of the micro-processor. A multiplexer 3 is coupled to said analog digital circuitry 5 and conditioned inputs. The resulting signals output from said multiplexer, are transmitted to an analog to digital converter 5 of a conventional design. The resulting digital signal is transmitted to a microprocessor 6 via optically isolated circuits for further signal processing within the micro-processor. The input of the transmitter 8 is coupled to said microprocessor 6 for transmission to the receiver connected to the mold controller. While described in reference to the above identified components, the present invention can be used with other and different configurations which will be known to those skilled in the art. Thus, the present invention is limited only by the claims set forth below.