JPS6331320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load cell that detects a load through the amount of elongation of a frame of a press machine.

Various types of load cells have been proposed in the past as this type of load cell. For example, load cells that use mechanical elongation detectors, such as dial gauge type and tilt type, are relatively inexpensive;
The amount of elongation is easily affected by temperature, and malfunctions are likely to occur due to vibrations during press operation. For this reason, this type of mechanical type has the drawback of not being able to follow rapid load fluctuations such as during punching, and having poor detection accuracy. In addition to the above-mentioned mechanical type, the elongation (load) detector includes a capacitance type, a strain gauge type, an optical type, a differential transformer type, a rotary encoder type, and the like. However, all of these devices have high detection accuracy but are expensive and have the drawbacks of being restricted in the environment in which they can be installed.

The present invention has been made in view of the above, and includes:
The purpose of the present invention is to provide a load meter for a press machine that has a simple structure, is inexpensive, and is capable of high-precision measurement.

The present invention will be described below with reference to an illustrated embodiment.

In the figure, 1 is a frame of a C-type frame press, and a load detector 4 is installed between the lower end of a detection rod 2 whose upper end is fastened and fixed to the side surface of the frame 1 and a fixed arm 3 fixed to the side surface of the frame 1. It is installed.

The load detector 4 has a Hall element fixing case 6 fixed to the detector body case 5 fixed to the upper end of the fixed arm 3 with screws 7, and a hole element fixed case 6 formed at the center of the upper surface of the fixed case 6. A Hall IC 9 as a Hall element is installed in the recess 8.
10 is an output terminal of a Hall IC provided in the fixed case 6.

A cover 12 that holds the plunger 11 so as to be freely retractable is attached to the upper surface of the detector main body case 5 by screws 13.
It is tightened and fixed. Further, the upper end of the actuating plunger 14 passed through the upper wall of the main body case 5 is brought into contact with the inner end surface (lower end surface) of the plunger 11, and the permanent magnet 15 fixed to the lower end of the actuating plunger 14 is placed in the recess 8. Hall IC facing inside
It corresponds to 9 in proximity. By tensioning a return spring 17 between the spring receiver 16 fixed near the upper end of the operating plunger 14 and the upper wall surface of the main body case 5, both the plungers 11 and 14 are biased to protrude. The upper end surface of the plunger 11 is held in contact with the lower end surface of the detection rod 2, and a permanent magnet 15 is disposed to follow the plunger 14.

In such a load detector 4, when a load is applied to the slide supported by the frame 1, the frame 1 expands and contracts due to the reaction force of this load. Then,
Since the upper end fixed portion of the detection rod 2 and the fixed arm 3 come into contact with each other, the plunger 11, which is held in contact with the lower end surface of the detection rod 2, is moved in and out while being held by the return spring 17. Then, as the actuating plunger 14 moves up and down, the permanent magnet 15 fixed to the lower end of the plunger moves into the hole.
Connect to and separate from IC9.

Here, from one output terminal connected to the Hall IC 9, as the magnetic flux density changes due to a change in the relative distance between the permanent magnet 15 and the Hall IC 9, a change occurs as shown by characteristic line A in Fig. 3. At the same time, the other output terminal outputs a voltage that changes as shown by characteristic line B in the figure. Also, since the rate of change of both voltages is constant, the difference between the voltages output from both output terminals is determined by the difference between the permanent magnet 15 and the hole, as shown by characteristic line C in Figure 3.
It linearly decreases gradually as the relative distance to IC9, that is, the amount of extension of the frame that is proportional to the load on the slide increases. Therefore, if the output voltage according to this characteristic line C is converted into a load, the load on the slide can be detected.

Here, in the present invention, the output voltage of the detector 4 is converted into a load value by a control device 17 as shown in FIG. 4, for example.

That is, each output terminal 10 of the detector 4 is connected to the input terminal of the differential amplifier 18 to amplify the difference voltage between the terminals, and the temperature correction circuit 19 performs temperature correction on this amplified voltage. The voltage corrected in this way is sampled and held by the sample hold circuit 20 and the peak hold circuit 2.
1, respectively.

Further, a measurement range is set by a rotary cam limit switch 22 linked to the main shaft of the press machine, etc., and one pulse is applied to the gates 23 and 24 of each of the hold circuits 20 and 21 at the beginning of this measurement range. Then, the sample and hold circuit 20 samples the input voltage when the pulse is input and holds it after the pulse is input, and the peak hold circuit 21 holds the peak value of the input voltage after the pulse is input.

After the outputs of the sample hold circuit 20 and the peak hold circuit 21 are subtracted by a differential amplifier 25, the outputs are converted into tonnage by a load converter 26. Note that the signal thus converted is converted into a digital quantity by the A/D converter 27 and digitally displayed on the display 28.

On the other hand, the output of the load converter 26 is input to the comparator 3 together with the output of the overload setting device 29.
Enter 0. When the output of the load converter 26 becomes larger than the output of the setting device 29, that is, when the amount of elongation of the frame 1 in response to the load of the press machine reaches a permissible value or more, the indicator lamp 31
At the same time, the external output contact 32 is activated to output a stop signal to the press machine.

Furthermore, when the measurement range is outside the measurement range set by the rotary cam switch 20, a signal is applied from the gate 33 to the latch circuit of the A/D converter 27 to hold it, so the display 28 continues to display unless the power is turned off. . Also, within the measurement range, the hold is released and a new peak value is sampled.

Then, in the next measurement, the sample hold circuit 20 and the peak hold circuit 21 are connected to each circuit 2.
Since the same input voltage at the start of measurement is sampled by one pulse from the rotary cam switch 22 inputted to the gates 0 and 21, the output of the differential amplifier 25 automatically becomes zero. For this reason, the displacement amount for each cycle is peak-held and displayed every time. Reference numeral 34 denotes an inverter for inputting a check voltage to the NAND circuit 35, which is provided to check for disconnection of the detector 4.

That is, since the output of the detector 4 is an analog voltage responsive to the load, temperature correction and other processing circuits are simplified. For this reason, the control device 17 is simplified and the detection device can be provided at low cost.

Furthermore, since the detector 4 is of a non-contact type and has extremely high responsiveness, it can sufficiently respond to rapid changes in load accompanied by vibrations and the like. For this reason, measurement accuracy and reliability can be sufficiently increased.

On the other hand, in the control device 17, the sample hold circuit and the peak hold circuit start operating at the same time in response to a command from the rotary cam limit switch for each cycle of the press machine, and sample the same voltage output from the detector. Since the output of the differential amplifier becomes zero every cycle and the display is reset to zero, measurement errors due to various environmental factors such as temperature are extremely small. Therefore, the amount of displacement of the load is accurately displayed on the display for each cycle.

When an overload occurs, an indicator lamp lights up to indicate this, and at the same time a stop signal is output to the press machine, thereby preventing various troubles due to overload operation.

Incidentally, when the press machine is a straight side press as shown in FIG. 5, the amount of elongation of the frame 1 is relatively small. Therefore, in such a case,
By lengthening the detection rod 2 and the fixed arm 3 and increasing the fixed interval between them, the amount of elongation of the frame 1, that is, the detection accuracy of the load of the press machine can be increased.

As explained above, according to the present invention, the detector is composed of a permanent magnet and a Hall element, and the load of the press machine is detected through the analog output voltage that responds to the relative distance between them. Not only can reliability against vibrations and the like be improved, but also rapid load fluctuations can be accurately detected. In addition, the output of the peak hold circuit that holds the output peak from the detector and the output of the sample hold circuit are output to the load converter via a differential amplifier, and the output is simultaneously output to both hold circuits for each cycle. Since the operation start signal (one pulse) is output from the rotary cam limit switch, the output of the differential amplifier, that is, the display on the display, is automatically returned to zero after each cycle, which increases the accuracy and reliability of load detection and display. and can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a C-frame press equipped with the present invention. FIG. 2 is a sectional view showing a specific example of a load detector. FIG. 3 is an output characteristic diagram of the same detector as above. FIG. 4 is a block diagram of an electric circuit showing one embodiment of the present invention. FIG. 5 is a perspective view of a straight-sided press equipped with the present invention. 1... Frame, 4... Load detector, 9... Hall
IC, 15... Permanent magnet, 20... Sample hold circuit, 21... Peak hold circuit, 22... Rotary cam limit switch, 25... Differential amplifier, 2
6...Load converter, 28...Display device, 29...Overload setter, 30...Comparator, 31...Display lamp, 32...External output contact.

Claims (1)

[Claims] 1. A load detector composed of a permanent magnet and a Hall element whose relative distance changes according to the amount of elongation of the frame of the press machine, and a sample hold circuit and a peak hold circuit to which the output from the load detector is supplied. A rotary cam limit switch that controls the activation timing of both hold circuits, a differential amplifier and a load converter that subtracts the output of both hold circuits and converts it into a load value, and displays the load output from the load converter. an indicator lamp that indicates an overload condition when the load output from the load converter reaches a predetermined value or more; and an external device that outputs a stop signal to the press machine in synchronization with the operation of this indicator lamp. A load cell for a press machine equipped with an output contact.