JP2008284705A - Pressure detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure detection device which has a simple system, can continuously obtain a pressure detection signal, and highly maintains reliability by reducing the risk of failure of electronic parts. <P>SOLUTION: The pressure detection device is provided with a converter unit having a load cell 6 for detecting the pressure applied on an injection screw, an amplifier 24 which is provided separately from the load cell 6 and amplifies a detection output of the load cell, an A/D converter 25 for converting an analog output signal of the amplifier to a digital signal, and a transmission part 26 for transmitting the output signal from the A/D converter 25 as a pressure detection signal. The load cell 6 always detects the pressure, and the converter unit 23 continuously transmits the pressure detection signal to a control device 30 based on the detection output of the load cell 6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pressure detection device for detecting pressure applied to an injection screw during pressure molding, particularly in an electric injection molding device.

  As an electric injection molding device, the rotation of the servo motor is converted into a linear motion via a ball screw mechanism or the like in which a nut member is attached to the screw shaft, and the injection screw in the heating cylinder is driven in its axial direction. Some perform pressure molding (see, for example, Patent Document 1). In this electric injection molding device, the pressure applied to the injection screw is detected by a load cell provided between the ball screw mechanism and the injection screw, and the deviation between the detected pressure value and a preset pressure command value is calculated. Then, the control of the injection pressure and the like in the injection process is performed by giving a feedback to the detected pressure value by giving a control signal for matching the detected pressure value to the pressure command value to the servo motor.

Further, as a device for detecting the pressure applied to the injection screw, as shown in Patent Document 2, a load cell, an amplifier that is integrally attached to the load cell, amplifies the output of the load cell, and an analog signal of the amplifier is digitally converted. A load cell unit comprising an A / D converter for converting signals, serial communication means for sending output signals from the A / D converters as serial data signals, and a box having an arithmetic control unit for controlling them Are arranged. In this pressure detection device, a control device connected to the load cell unit through a transmission cable is arranged, and the control device supplies power to the load cell unit and sends out a control signal. Then, the arithmetic control unit controls the amplifier, the A / D converter and the serial communication means by this control signal, and sends the output of the load cell to the control device side. That is, in the pressure detection device, the load cell unit and the control device are configured to communicate bidirectionally.
Japanese Patent No. 3166632 Japanese Patent No. 3810993

  By the way, when detecting the pressure applied to the screw in the pressure detection device of the conventional electric injection molding device, first, a start signal is sent from the control device to the load cell unit, and this load signal is sent from the load cell unit to the control device. Since the pressure detection signal is transmitted, in order to obtain the pressure detection signal, one-way communication for exchanging information from both directions is required, and the system is complicated. In addition, since the load cell unit and the control device communicate bidirectionally via a single transmission cable connecting them, when a signal is sent from either one, the other sends a signal. There is a drawback that the continuous pressure detection signal cannot be reflected in the control of the servo motor. For this reason, there existed a subject that the control precision of a servomotor fell and the quality of a molded product will vary.

  Further, in the conventional pressure detection device, as described above, electronic components such as an amplifier, an A / D converter, a serial communication unit, and an arithmetic control unit are arranged in a box attached integrally with the load cell. For this reason, the impact due to the pressure received by the load cell and the heat generated by the impact are directly transmitted to these electronic components, which may cause the electronic components to fail and lack reliability.

  In view of such circumstances, the present invention is simple and easy to handle, and can continuously improve the accuracy of servo motor control by obtaining a pressure detection signal. Provided is a pressure detection device in an electric injection molding apparatus capable of reducing the risk of failure and maintaining high reliability.

In order to solve the above problems, the present invention proposes the following means.
That is, a pressure detection device according to the present invention is a pressure detection device that detects a pressure applied to an injection screw of an electric injection molding device and sends it to a control device, and a load cell that detects a pressure acting on the injection screw; An amplifier that is provided separately from the load cell, amplifies the detection output of the load cell, an A / D converter that converts an analog output signal of the amplifier into a digital signal, and an output from the A / D converter A conversion unit including a transmission unit that transmits a signal as a pressure detection signal, the load cell constantly detects pressure, and the conversion unit continuously detects the pressure based on the detection output of the load cell. A signal is sent to the control device.

  In the pressure detection device of the present invention, the load cell detects the pressure applied to the injection screw, the detection output is amplified and digitally converted by the conversion unit, and sent to the control device as a pressure detection signal by the transmission unit. The signal is transmitted in only one direction from the conversion unit to the control device. Therefore, since a one-way communication is not required as in the prior art in order to obtain a pressure detection signal, the system can be simplified.

  Furthermore, in addition to the signal being transmitted from the conversion unit to the control device in only one direction, the load cell constantly detects the pressure applied to the injection screw, so the detection output is continuous, The pressure detection signal based on the detection output can be continuously sent to the control device without interruption. Therefore, since this continuous pressure detection signal can be reflected in the feedback control, it becomes possible to continuously grasp the deviation between the pressure detection value and the predetermined pressure command value, and the control accuracy of the servo motor can be improved. Can be improved.

  Furthermore, in the pressure detection device, the conversion unit including the amplifier, the A / D converter, and the transmission unit, which are electronic components that are vulnerable to shock and heat, is provided separately from the load cell. Since the impact due to the pressure received and the heat generated thereby are not directly transmitted to the electrical component, the risk of failure can be reduced and the lifetime can be extended.

  Further, in the pressure detection device according to the present invention, the conversion unit includes a power supply unit that supplies power to the load cell, the amplifier, the A / D converter, and the transmission unit. It is a feature.

  The power supply unit provided in the conversion unit is configured to collectively supply power to each part of the load cell and the conversion unit. Conventionally, power supply was performed from the control device side to the load cell side via the same cable that transmits the signal, but by transmitting the power supply unit on the conversion unit side, it is transmitted via the cable. Since only the pressure detection signal sent from the conversion unit side to the control device side is performed, the system can be further simplified, and noise generated by propagating power through the cable can be reduced. Since there is no need to consider the influence, highly reliable signal transmission is possible.

  According to the pressure detection device of the present invention, since the signal is transmitted only in one direction from the conversion unit to the control device, the system becomes simple and easy to handle, and the pressure applied to the injection screw by the load cell is always applied. Since it is possible to detect and continuously obtain a pressure detection signal based on the detection signal, it is possible to improve the control accuracy of the servo motor and to prevent variations in the quality of the molded product. Furthermore, since the conversion unit including the electronic components is disposed separately from the load cell, it is possible to reduce the risk of failure due to impact or heat and maintain high reliability.

  Hereinafter, an embodiment of a pressure detection device according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram of an electric injection molding apparatus in which the pressure detection device according to the present embodiment is used, and FIG. 2 is a block diagram showing the pressure detection device according to the present embodiment.

  In FIG. 1, reference numeral 1 denotes an electric injection molding apparatus, which is provided with a conversion unit 23 and a control apparatus 30, which will be described later. The electric injection molding apparatus 1 includes a heating cylinder 4 attached to a support plate 2 and having an injection nozzle 3 at the tip, an injection screw 5 inserted into the heating cylinder 4 so as to be movable in the axial direction thereof, and the injection A support base 7 that supports the rear end side (right side in FIG. 1) of the screw 5 via a load cell 6 is provided. A pair of screw shafts 12 a are rotatably supported on the support plate 2 and the support plate 8 disposed on the rear end side so as to face the support plate 2, and each screw shaft 12 a is fixed to both ends of the support base 7. Is engaged with the ball nut 12b. The screw shaft 12a and the ball nut 12b constitute a ball screw mechanism 12 that converts the rotation of the servo motor 11 into a linear motion.

  A pulley 13 is attached to the rear end of each screw shaft 12a, and a timing belt 15 is stretched between the pulley 13 and a pulley 14 attached to the rotation shaft of the servo motor 11. Thus, the rotation of the servo motor 11 is transmitted to the pulley 13.

  Moreover, the pressure detection apparatus 10 in this embodiment is comprised from the load cell 6 and the conversion unit 23, as shown in FIG. The load cell 6 includes, for example, four strain gauges 21, and the strain gauges 21 are connected so as to form a known Wheatstone bridge circuit 20 as schematically shown in FIG. One strain gauge 21 is arranged on each side of the eatstone bridge circuit 20. A constant input voltage is input from the power supply unit 27 described later to the two opposing terminals 20 a and 20 b in the Wheatstone bridge circuit 21, and the resistance value of the strain gauge 21 due to the pressure applied to the load cell 6. The output voltage between the remaining terminals 20c and 20d is changed in accordance with the change in. This output voltage is sent to the conversion unit 23 as a detection output of the load cell 6.

  The conversion unit 23 includes an amplifier 24, an A / D converter 25, a transmission unit 26 and a power supply unit 27. The conversion unit 23 is installed separately from the load cell 6. The amplifier 24 amplifies the detection output of the load cell 6 sent from the conversion unit 23, and the A / D converter 25 converts the analog signal output from the amplifier 24 into a digital signal. In the present embodiment, the transmission unit 26 is a serial I / O that sends the output of the A / D converter 25 as a serial data signal to the control device 30, and the serial data signal is used as the detection output of the load cell 6. The pressure detection signal is input to the control device 30. The power supply unit 27 supplies power to the terminals 20a and 20b of the Wheatstone bridge circuit 21 of the load cell 6 as an input voltage, and the amplifier 24, A / A provided in the conversion unit 23 as well as the power supply unit 27. The D converter 25 and the transmitter 26 are also configured to supply power.

  Then, the control device 30 calculates a deviation between the pressure detection value based on the pressure detection signal sent from the transmission unit 26 of the conversion unit 23 and a preset pressure command value, and applies a pressure to the servo motor 11. Pressure feedback control is performed to make the detected value coincide with the pressure command value.

  When the electric injection molding apparatus 1 operates, the servo motor 11 rotates, and the rotation is transmitted to the screw shafts 12a via the timing belt 15 and the pulleys 13 and 14, and the screw shaft 12a Due to the rotation, the support base 7 linearly moves in the direction of the screw shaft 12a through the ball nuts 12b attached thereto. The injection screw 5 is inserted into the injection screw 5 via a load cell 6 held so as to be sandwiched between the rear end side (right side in FIG. 1) and the front end side (left side in FIG. 1) of the support base 7. The molding operation is performed by moving forward or backward in the axial direction.

  When the electric injection molding apparatus 1 is in operation, an input voltage is always supplied to the terminals 20 a and 20 b of the Wheatstone bridge circuit 20 of the load cell 6 by the power supply unit 27 provided in the conversion unit 23. Yes. Further, the potential difference generated at the terminals 20c and 20d is the output voltage. When no pressure is applied to the injection screw 5, the Wheatstone bridge is in an equilibrium state. Therefore, the potential difference between the terminals 20c and 20d is Does not occur. On the other hand, when pressure is applied to the injection screw 5, the pressure is applied to the load cell 6 sandwiched between the injection screw 5 and the support base 7, and distortion is caused according to the magnitude of the pressure. The resistance value of the gauge 21 changes and a potential difference is generated between the terminals 20c and 20d. This potential difference becomes the output voltage of the Wheatstone bridge 20 and is sent to the conversion unit 23 as the detection output of the load cell 6. Accordingly, a change in pressure applied to the injection screw 5 is continuously sent to the conversion unit 23 as a detection output by the load cell 6.

  The value of the detection output by the load cell 6 is very small because it is based on a minute change in the resistance value of the strain gauge 21. Therefore, when the detection output is input to the conversion unit 23, the output is first amplified by the amplifier 24. Next, the amplified detection output is converted from an analog output signal into a digital signal by the A / D converter 25, and further converted into a serial data signal by the transmission unit 26, so that the control device is used as a pressure detection signal. 30. Thus, since the pressure detection signal is transmitted through digitization or serial data, it is less affected by noise or the like, and signal transmission with high reliability can be achieved. In addition, since the pressure detection output from the load cell 6 is continuously input to the conversion unit 23, the pressure detection signal sent from the conversion unit 23 to the control device 30 is also continuous. Then, based on the continuous pressure detection signal, the control device 30 performs pressure feedback control, so that an optimal control signal is given to the servo motor 11 and high-precision molding can be performed.

  Further, the value of the detection output sent from the load cell 6 to the amplifier 24 of the conversion unit 23 is very small and easily affected by noise or the like, but the conversion unit 23 is installed near the load cell 6 and the length of the cable 31 is increased. For example, by using a shielded cable having a length of 50 cm or less and shortly connecting, it is possible to easily prevent the influence of noise or the like received by the pressure detection signal in the previous stage of digitization.

  In the pressure detection device 10 of the present invention, the load cell 6 detects the pressure applied to the injection screw 5, and the detection output is amplified, converted into digital data and converted into serial data by the conversion unit 23, and then the control device is used as a pressure detection signal. Therefore, the signal is transmitted only in one direction from the conversion unit 23 side to the control device 30. Accordingly, since it is not necessary to perform one round-trip communication as in the prior art in order to obtain the pressure detection signal, the system of the pressure detection device 10 can be simplified.

  Furthermore, in addition to the signal being transmitted from the conversion unit 23 to the control device 30 in only one direction, the load cell 6 constantly detects the pressure of the injection screw 5, so that the detection output is continuous. The pressure detection signal based on the detection output is also continuously sent to the control device 30 without interruption. Therefore, since this continuous pressure detection signal can be reflected in the feedback control, it becomes possible to continuously grasp the deviation between the pressure detection value and the predetermined pressure command value, and the control accuracy of the servo motor 11 is improved. Can be improved.

  Furthermore, in the pressure detection device 10, the conversion unit 23 including the amplifier 24, the A / D converter 25, the transmission unit 26, and the power supply unit 27, which are electronic components vulnerable to impact and heat, is separate from the load cell 6. Since it is provided as a body, the impact caused by the pressure received by the load cell 6 and the heat generated thereby are not directly transmitted to these electrical components, so the risk of failure can be reduced and the life of the load cell 6 can be extended. It becomes possible.

  In the present embodiment, the power supply unit 27 provided in the conversion unit 23 is configured to collectively supply power to each part of the load cell 6 and the conversion unit 23. In the present embodiment, by arranging the power supply unit 27 in the conversion unit 23, what is transmitted via the cable connecting the conversion unit 23 and the control device 30 is sent from the conversion unit 23 side to the control device 30 side. Since only the detected pressure detection signal is obtained, the system can be further simplified.

  From the above, according to the pressure detection device 10 according to the present embodiment, since the signal is transmitted only in one direction from the conversion unit 23 to the control device 30, the system is simplified and handling is facilitated. Since the pressure of the injection screw 5 can be detected and a pressure detection signal based on the detection signal can be obtained continuously, the control accuracy of the servo motor 11 can be improved, and the quality of the molded product can be improved. Become. Furthermore, since the conversion unit 23 is disposed separately from the load cell 6, it is possible to reduce the risk of failure due to impact or heat and maintain high reliability.

  In addition, since the pressure detection signal is sent through digitization or serial data, highly reliable signal transmission can be performed.

It is a schematic block diagram of the electric injection molding apparatus in which the pressure detection apparatus which concerns on this embodiment is used. It is a block diagram which shows the pressure detection apparatus which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric injection molding apparatus 5 Injection screw 6 Load cell 10 Pressure detection apparatus 23 Conversion unit 24 Amplifier 25 A / D converter 26 Transmission part 27 Power supply part

Claims (2)

In the pressure detection device for detecting the pressure applied to the injection screw of the electric injection molding device and sending it to the control device,
A load cell for detecting the pressure applied to the injection screw;
An amplifier that is provided separately from the load cell, amplifies the detection output of the load cell, an A / D converter that converts an analog output signal of the amplifier into a digital signal, and an output from the A / D converter A conversion unit including a transmission unit that transmits a signal as a pressure detection signal,
The pressure detection device, wherein the load cell constantly detects pressure, and the conversion unit continuously sends the pressure detection signal to the control device based on the detection output of the load cell.   The pressure detection device according to claim 1, wherein the conversion unit includes a power supply unit that supplies power to the load cell, the amplifier, the A / D converter, and the transmission unit. .

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