JPH09272144A - Offset controlling method of load cell in injection molder - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To facilitate and surely perform offset adjustment by performing offset adjustment (zero-point adjustment) of a load cell by software. A load cell for detecting a pressure applied to a screw in a heating cylinder is provided, and rotation of an electric servomotor is converted into a linear motion by a rotation → linear motion conversion mechanism using a screw mechanism and transmitted to the screw. In the injection molding machine configured as described above, in a state where it can be considered that the pressure from the resin is not applied to the screw, the load cell is rotated even if the electric servomotor is rotated forward and reverse by rotating the electric servomotor. To detect the rotational position where the detected value does not change,
The detected value by the load cell at the rotational position where the detected value does not change is automatically updated and held as 0 point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell offset adjusting method in an injection molding machine, and more specifically, it converts the rotation of an electric servomotor into a linear motion by a rotation-linear motion conversion mechanism using a screw mechanism. In the injection molding machine that takes the structure to transmit to the screw,
The present invention relates to a load cell offset adjustment method in which a load cell offset adjustment (zero-point adjustment) for detecting a pressure applied to a screw is performed by software.

[0002]

2. Description of the Related Art In an in-line screw type injection molding machine, as a method of measuring a resin pressure, there are a method of directly measuring a resin pressure and a method of measuring a pressure applied to a screw by a load cell. However, in the former method of directly measuring the resin pressure, there is a problem that the resin pressure sensor used is expensive and easily broken, and the installation work of the resin pressure sensor is complicated, and the behavior of the molten resin is also adversely affected. I have a concern.

Therefore, in an in-line screw type injection molding machine, a load cell is arranged on the rear end side of the screw, and the force applied to this load cell is measured as a pressure value corresponding to the resin pressure applied to the tip of the screw. It is common to take

The pressure value detected by the load cell is the injection stroke (the primary injection stroke and the subsequent pressure-holding stroke).
Used as a monitoring value for pressure control in. Therefore, if the detection value of the load cell deviates, the molding conditions itself will change. Therefore, when the machine (injection molding machine) is shipped or the load cell is replaced, the load cell offset adjustment (0 point correction) is performed and the bolt tightening to the load cell is performed. It is designed to absorb variations in torque and variations in parallelism of the load cell mounting surface. Then, the offset adjustment of the load cell is performed by adjusting the load cell amplifier to 0.
It was done by a hardware method by manually adjusting the point adjustment volume (variable resistor).

[0005]

By the way, as described above, even if the offset adjustment of the load cell is performed at the time of assembling the machine or replacing the load cell, the detected value of the load cell (detection output of 0 point) becomes A gap occurs. That is, for example, due to repeated loading, the contact state between the mounting bolt and the load cell changes (the bolt tightening torque changes due to conforming), and the adhesive with the strain gauge used in the load cell ages. By doing so, a deviation occurs in the detection output of the load cell.

For this reason, the load cell offset adjustment (0 point adjustment) was performed by adjusting the 0 point adjustment volume of the load cell amplifier at the time of periodic inspection, but it is pointed out that the workability is poor due to the manual adjustment. was there. In addition, it was pointed out that the workability of adjusting the offset when assembling the machine or exchanging the load cell was similarly poor.

[0007] The present invention has been made in view of the above points,
The purpose thereof is to facilitate and surely perform the offset adjustment by performing the offset adjustment (zero-point adjustment) of the load cell by software.

[0008]

In order to achieve the above-mentioned object, the present invention comprises a load cell for detecting the pressure applied to a screw in a heating cylinder, and uses a screw mechanism to rotate an electric servomotor. In an injection molding machine configured to convert linear motion by a rotation-to-linear motion conversion mechanism and transmit it to the screw, the electric servomotor rotates forward and backward when it can be considered that the pressure from the resin is not applied to the screw. By doing so, it is necessary to find a rotational position where the detected value by the load cell does not change even though the electric servo motor is rotating.
The detected value by the load cell at the rotational position where the detected value does not change is automatically updated and held as 0 point.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a main part configuration of an inline screw type injection molding machine according to an embodiment of the present invention (hereinafter referred to as the present embodiment).

In FIG. 1, 1 is a heating cylinder, 2 is a screw arranged in the heating cylinder 1 so as to be rotatable and forward / backward, 3 is a servomotor as an injection drive source, 3a is a servomotor 3. The output pulley 4 is a timing belt for transmitting the rotation of the output pulley 3a to the pulley 5a of the linear-to-linear movement conversion mechanism 5, and the reference numeral 5 is a ball screw mechanism for converting the rotational movement into the linear movement and transmitting it to the screw 2. → Linear motion conversion mechanism, 6
Is an encoder for detecting the rotation of the servomotor 3, 7 is a load cell for detecting the resin pressure applied to the tip of the screw 2, and 8 and 9 are A / D converters.

Reference numeral 10 denotes an offset processing unit embodied by a function such as a microcomputer, which is a load cell output correction calculation unit 10a.
And an offset amount storage unit 10b and an offset value confirmation determination unit 10c. 11 is an injection condition setting storage unit that is also embodied by a function of a microcomputer, 12 is an injection feedback control unit, 13 is a D / A converter, 14 is a servo amplifier, and 15 is an automatic embodied function of a microcomputer. It is an offset operation control unit.

The offset processing unit 10 includes a load cell 7
Is input via the A / D converter 9, and in the load cell output correction calculation unit 10a, the offset amount storage unit 10b
The output of the load cell 7 is corrected and calculated with reference to the data value stored in, and pressure (resin pressure) data is calculated. In the offset amount storage unit 10b, in the automatic offset processing operation by the automatic offset operation control unit 15, which will be described later in detail, the electric servo motor 3 is provided in a state in which it can be considered that the pressure from the resin is not applied to the screw 2. The output value N of the load cell 7 is stored in a rewritable form at a rotation position where the output value (detection value) of the load cell 7 does not change even though the electric servomotor 3 is rotated in the forward and reverse directions. And load cell output correction calculation unit 10
a corrects the output of the load cell 7 by setting this value N to 0 (that is, assuming that the pressure is 0). In the automatic offset processing operation described later in detail, the offset value confirmation determination unit 10c determines that the output value (detection value) of the load cell 7 does not change even though the electric servomotor 3 is rotated. Determine, load cell 7 at this time
The output value N of is stored in the offset amount storage unit 10b.

The injection condition setting storage unit 11 rewritably stores the control conditions for the primary injection stroke and the subsequent pressure-holding stroke. In this example, for example, the primary injection control condition is injection. Injection speed according to the screw stroke from the start position (injection speed set in multiple stages)
And the primary pressure (that is, the upper limit monitoring pressure value of the primary injection) are set and stored, and the holding pressure control condition is a holding pressure according to the time from the holding pressure switching point (a holding pressure set in multiple stages). Pressure) is set and stored.

The injection feedback control unit 12 has setting data stored in the injection condition setting storage unit 11 and speed data obtained by appropriately converting the output of the encoder 6 via the A / D converter 8 and the like. Output of load cell 7 is A / D
Based on the pressure data obtained via the converter 9 and the offset processing unit 10, a control signal is generated and D /
It outputs to the servo amplifier 14 via the A converter 13, and drives and controls the servo motor 3. As a result, in the primary injection stroke, the injection feedback control unit 12 drives and controls the servomotor 3 via the servo amplifier 14 so that the measured speed data matches the injection speed setting data, and also the pressure holding stroke. In (1), the servomotor 3 is drive-controlled via the servo amplifier 14 so that the actually held pressure data matches the holding pressure setting data.

The rotation of the servomotor 3 is controlled by the output pulley 3
a, rotation via belt 4 → linear motion conversion mechanism 5
Is transmitted to the pulley 5a, and the rotational movement is converted into the linear movement by the rotation → linear movement converting mechanism 5 and transmitted to the screw 2. As a result, in the primary injection stroke, the screw 2 is driven forward by feedback control so as to follow the set injection speed, and the molten resin stored on the tip side of the screw 2 in the known measurement stroke is transferred to the metal mold. It is injected and filled in the mold. Further, in the pressure-holding process, the pressure following the set pressure-holding pressure is applied to the screw 2
The forward pressure of the screw 2 is controlled by feedback control so that it is applied to the resin in the mold via the.

Next, the automatic offset processing operation of the load cell 7 according to this example will be described. For example, when the operator has instructed the start of the automatic offset processing operation interactively with a predetermined screen of a display device attached to the machine when the periodic inspection time comes, the automatic offset operation control unit 15 recognizes this and Start the automatic offset processing operation.

In this example, the automatic offset processing operation is possible even when the heating cylinder 1 is clogged with resin, that is, the automatic offset processing operation can be performed without time-consuming resin removal. Therefore, the automatic offset operation control unit 15 forcibly retracts the screw 2 by a predetermined stroke by the electric servomotor 3 when the high-pressure resin is stored on the tip side of the screw 2. First, a state where no resin pressure is applied to the screw 2 (by causing a so-called suck back operation) is first set in the machine.

Then, in a state where it can be considered that the pressure from the resin is not applied to the screw 2, the automatic offset operation control unit 15 rotates the electric servomotor 3 in the forward and reverse directions to rotate the electric servomotor 3. However, the electric servomotor 3 is controlled so as to find a rotational position where the output value of the load cell 7 does not change. The offset value confirmation determination unit 10c of the offset processing unit 10
While referring to the information from the automatic offset operation control unit 15 as necessary, it is determined that the output value of the load cell 7 does not change even though the electric servomotor 3 is rotated, and the output position is determined. The load cell output value N at the rotational position where the value does not change is automatically updated / held in the offset amount storage unit 10b as data corresponding to 0 point.

The rotational position where the load cell output value does not change even though the electric servomotor 3 is rotated will be described with reference to FIG. In this example, as described above, the rotation of the electric servomotor 3 is converted into the linear motion by the rotation → linear motion conversion mechanism 5 using the ball screw mechanism and transmitted to the screw 2. In a rotation-> linear motion conversion mechanism using a screw mechanism such as a ball screw mechanism, the nut body portion and the screw shaft portion are screw-coupled, and there is a place between the screw thread of the screw shaft portion and the screw thread of the nut body portion. There is a certain amount of clearance (clearance).

FIG. 2 is a view schematically showing the engagement relationship between the screw thread of the screw shaft portion and the screw thread of the nut body portion. In FIG. 2, 21 is the screw thread of the screw shaft portion, and 22 is the nut. The screw thread L of the body portion is the amount of play between the screw thread 21 and the screw thread 22. In the ball screw mechanism, the balls correspond to the screw threads 22 of the nut body, but here, for convenience of illustration, they are equivalently shown as the screw threads 22.

When the electric servomotor 3 is continuously rotating in one direction, that is, when the nut body of the screw mechanism is continuously rotating in one direction, FIG. 2A or FIG. (B), the screw thread 21 of the nut body portion abuts the screw thread 21 of the screw shaft portion, and the screw shaft portion receives thrust from the nut body portion. Therefore, in FIG.
In the state shown in (b), the screw 2 that moves forward and backward integrally with the screw shaft portion also receives a thrust from the nut body portion, and a force based on the rotational force of the electric servomotor 3 is applied to the load cell 7. Is in a state.

On the other hand, as shown in FIG. 2 (c), when the screw thread 21 of the screw shaft portion and the screw thread 22 of the nut body portion are not in contact with each other, the electric servomotor 3 is rotated. However (even if the nut body rotates), the screw shaft does not receive any thrust from the nut body. Therefore, the thread 22
As long as the nut body (electric servomotor 3) is rotating within the range of the play L that does not contact the screw thread 21, the load cell 7 receives no force based on the rotational force of the electric servomotor 3, The load cell output at this time can be regarded as that when the screw 2 is in an unloaded state.

In the present example, the load cell output in the state shown in FIG. 2C is fetched, and this is automatically updated / held in the offset amount storage unit 10b as data corresponding to 0 point. It is a thing.

Although the play amount L differs depending on the screw mechanism, in this example, the play amount L is about 3 ° of the electric servomotor 3.
It corresponds to the rotation angle of.

FIG. 3 is a diagram showing an example of the automatic offset processing operation according to this example. In FIG. 3, 31 is an output value of the load cell (shown here as a value converted into pressure), 32 is a rotation amount of the electric servomotor 3, and +
(Plus) indicates the direction of moving the screw 2 forward, and- (minus) indicates the direction of moving the screw 2 backward.
The horizontal axis of FIG. 3 represents time.

As shown in FIG. 3, first, the electric servomotor 3 is largely rotated in the backward direction (screw backward direction) to perform the suck back operation, so that the screw 2 is not pressured by the resin. After shifting, the electric servomotor 3 is stopped for a predetermined period. Subsequently, after rotating the electric servomotor 3 in the backward direction by a predetermined angle, the electric servomotor 3 is stopped for a predetermined period, and then the electric servomotor 3 is rotated in the forward direction (screw forward direction) by the predetermined angle. , The electric servomotor 3 is stopped for a predetermined period (control period T1). Similar to this control period T1, backward rotation → stop → forward rotation → stop is repeated as many times as necessary (in this example, only the next control period T2 is repeated). The state where the pressure from the resin is not applied is surely shifted (that is, it is confirmed that the load cell output in each stop period of the control periods T1 and T2 is substantially uniform).

Next, the control shifts to a control for finding a rotational position where the load cell output value does not change even though the electric servomotor 3 is rotated, and the electric servomotor 3 is moved.
The control shown in part A of FIG. On the lower side of FIG. 3, a part of the control of the part A is enlarged and shown.

When the control shown in the section A is entered, the electric servomotor 3 is slightly rotated in the backward direction, then the electric servomotor 3 is stopped for a short time, and then the electric servomotor 3 is slightly rotated in the forward direction. After that, the electric servomotor 3 is stopped for a short time (control period T3). In the control period T3, the electric servomotor 3 moves backward depending on the positional relationship between the screw thread 21 of the screw shaft portion and the screw thread 22 of the nut body portion when the electric servomotor 3 is stopped. Immediately after starting the rotation or immediately after starting the forward rotation, there is a range S in which the load cell output value does not change even though the electric servomotor 3 is rotated. That is, as shown in FIG. 2 (c),
The screw thread 21 of the screw body is different from the thread 21 of the nut body.
There is a non-contact state.

After the control period T3, the small reverse rotation → short stop → small forward rotation → short stop are repeated, but the rotation angle and the stop time are controlled so as to be gradually reduced, and then the minute reverse rotation is performed. → Micro stop → Micro forward rotation → Micro stop When the control period Tn is entered, the load cell output value does not change during the entire control period Tn even though the electric servomotor 3 is rotated. . That is, the play amount L in FIG. 2 is set so that the screw thread 22 of the nut body portion does not touch the screw thread 21 of the screw shaft portion.
Within the rotation range, the electric servomotor 3 slightly performs forward and reverse rotations, and at this time, the output value (detection value) N of the load cell 7 becomes constant.

Therefore, the output value N of the load cell 7 is equivalent to that when the screw 2 is in the unloaded state without any force based on the rotational force of the electric servomotor 3 being applied. As described above, the data corresponding to the 0 point is automatically updated and held.

In the above description, the automatic offset processing operation of the load cell 7 is performed at the time of regular inspection, but the automatic offset processing operation of this example can be performed at any time, and Of course, it can be performed at the time of assembling or replacing the load cell. Alternatively, when the machine is started up, the load cell 7 is detected when no load is applied to the screw 2 (a state where the resin is not supplied and the screw 2 is not in the forward limit or the backward limit). The value is the offset amount storage unit 1
When the value stored in 0b deviates from the permissible range and deviates, an alarm message prompting the automatic offset processing operation may be displayed to prompt the start of the automatic offset processing operation.

[0032]

As described above, according to the present invention, since the offset adjustment (correction of 0 point) of the load cell is performed by software, the offset adjustment can be easily and surely performed by anyone. Therefore, even if the detection value (output value) corresponding to the 0 point of the load cell deviates due to aging, the user can easily adjust the offset and maintain the resin pressure detection accuracy of the machine at a good level for a long period of time. You can Furthermore, the automatic offset processing operation can be performed without performing time-consuming resin removal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a main configuration of an inline screw type injection molding machine according to an embodiment of the present invention.

FIG. 2 is an explanatory view schematically showing an engagement relationship between a screw thread of a screw shaft portion and a screw thread of a nut body portion in a screw mechanism.

FIG. 3 is an explanatory diagram showing an example of an automatic offset processing operation in the embodiment of the present invention.

[Explanation of symbols]

 1 Heating Cylinder 2 Screw 3 Servo Motor 3a Output Pulley 4 Timing Belt 5 Rotation → Linear Motion Conversion Mechanism 5a Pulley 6 Encoder 7 Load Cell 8, 9 A / D Converter 10 Offset Processing Section 10a Load Cell Output Compensation Calculation Section 10b Offset Amount Storage Section 10c Offset value confirmation determination unit 11 Injection condition setting storage unit 12 Injection feedback control unit 13 D / A converter 14 Servo amplifier 15 Automatic offset operation control unit 21 Screw thread of screw shaft portion 22 Screw thread of nut body L Latter amount

Claims (1)

[Claims] 1. A screw comprising a load cell for detecting a pressure applied to a screw in a heating cylinder, and converting the rotation of an electric servomotor into a linear motion by a rotation-linear motion conversion mechanism using a screw mechanism. In the injection molding machine configured to transmit the electric power to the screw, the electric servomotor is rotated forward and reverse to rotate the electric servomotor in a state where it can be considered that the pressure from the resin is not applied to the screw. In spite of this, the rotation position where the detection value by the load cell does not change is found, and the detection value by the load cell at the rotation position where the detection value does not change is automatically updated and held as 0 point. A method for adjusting the offset of a load cell in a characteristic injection molding machine.