JPH05248926A - Mass variation measuring device - Google Patents

Abstract

PURPOSE:To measure accurately the mass variation of a specimen placed in a specific atmosphere such as in a furnace without being influenced by the buoyance due to the process gas or the drift existing in the load cell itself. CONSTITUTION:A specimen A is borne by a load cell 7 through a jig 6, and the vibration system is excited by a driving mechanism 8. The load W sensed by the load cell 7 is fed to a signal processing means 16, and the mass M of the mass point Y when this vibration system is assumed as a single vibration is determined. Time change of the mass (m) of the specimen A is observed from the time change of the mass M.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass change measuring device which is particularly useful for measuring the mass change of an object to be measured placed in a special atmosphere such as a furnace.

[0002]

2. Description of the Related Art For example, an injection molded body is an object to be measured placed in a furnace. The injection-molded body is obtained by mixing a raw material with wax and binding it into a predetermined shape, and is first subjected to dewaxing treatment in a furnace, and thereafter, preliminary or main sintering steps are performed. The dewaxing process is a process in which a process gas is filled in a vacuum-exhausted furnace to heat an injection molded body, and wax contained in the molded body is gradually evaporated to remove it under reduced pressure. The process of shrinking and solidifying a porous injection-molded body after dewaxing. At this time, if the temperature control and the pressure control are passed too quickly, the weight reduction and the shrinkage of the injection-molded body progress faster than expected, which causes the injection-molded body to crack. In the past, however, it was difficult to actually measure the change in the injection molded body in the furnace, so after the completion of sintering, the molded product taken out of the furnace was inspected for cracks, etc., and temperature control and pressure control were performed. I have tried to evaluate how it should be based on experience and feelings.

However, in such a method, the objectivity of the evaluation is poor, and there is a problem that it is difficult to improve the yield of products because the skill of a specific worker who is skilled in the work is beyond the limit. ..

Therefore, recently, a jig for holding the injection molded body in a suspended state in the furnace is inserted, and the upper end of the jig is carried by the load cell to continuously apply the load applied to the upper end of the jig. A weight measuring device has been developed for detecting the weight. In this device, the mass of the object to be measured can be indirectly obtained by weighing.

[0005]

However, the furnace is often filled with high-pressure processing gas and the like, and the object to be measured is generally in a state of being subjected to buoyancy from these gases. . This buoyancy F can be expressed by F = ρ × V, where ρ is the gas density and V is the volume of the object to be measured. Therefore, accurate measurement of the mass is impossible unless the influence of buoyancy is removed from the detection result of the above-described measuring device. However, the gas density in the furnace is not always constant, and the volume of the object to be measured changes every moment during the sintering process, etc., so the buoyancy is calculated and the measurement results are properly compensated. Things are generally difficult. In addition, in this type of measuring device, there is gain drift and null drift in the load cell, which is a major component, and even in jigs,
Since the pressure difference between the inside and outside of the tight box is applied, it is more difficult to compensate due to these error factors.

It is an object of the present invention to provide a mass change measuring device capable of overcoming these problems and performing accurate measurement.

[0007]

The present invention adopts the following constitution in order to achieve the above object.

That is, the mass change measuring apparatus according to the present invention comprises a load cell for holding an object to be measured through a jig which is an elastic body, an excitation control means for intermittently exciting the object to be measured, and an excitation device for this excitation. The control means includes a signal processing means for detecting the vibration waveform of the load appearing in the load cell when the object to be measured is excited and calculating the mass of the mass point from the cycle T and the damping constant n. And

[0009]

The signal processing means determines the vibration period and the damping constant from the vibration waveform appearing in the detected load of the load cell.
Then, the mass of the mass point is calculated based on the equation of motion from these values and the elastic modulus of the vibration system given in advance. This mass is a value of a wide concept that includes the mass of the jig etc. in addition to the mass of the object to be measured, but its change with time does not change as long as there are no other mass change factors in the vibration system. It corresponds to the change in mass. Moreover, according to such a measurement method, since the terms such as the buoyancy acting on the object to be measured in the measurement process, the gain and zero point of the load cell, and the differential pressure acting on the jig are not included, the influence of the buoyancy and the load cell The influence of drift etc. can be excluded from the measurement.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example in which the mass change measuring device is applied to a heat treatment furnace in general. In a furnace 1, a heat insulating material 3 is arranged in a chamber 2, and a tight box 5 heated by a heater 4 is arranged inside the heat insulating material 3. In the tight box 5, a sample A such as an injection molded body is prepared. It is adapted to be able to carry out various processes such as dewaxing and sintering. In the figure, Q indicates the flow of the processing gas brought into contact with the sample A. On the other hand, the mass change measuring apparatus of the present embodiment uses the sample A in order to measure the mass change of the sample A.
Is supported by the load cell 7 in a suspended state via a jig 6 which is an elastic body, and the load cell 7 is held so as to be vertically movable by a drive mechanism 8 to detect the load applied to the load cell 7.

The jig 6 has a slit 9b in the top plate 9a and a receiving frame 9 containing the sample A therein, and a sub-chamber 10.
To chamber 1, tight box 5 and slit 9b
The probe 11 has a lower end portion 11b hung in the receiving frame 9 via a spring, and a spring 12 for elastically carrying the upper end portion 11a of the probe 11 on the measuring end 7a side of the load cell 7. Has a diameter larger than that of the slit 9b and is attached to the lower surface of the top plate portion 9a of the receiving frame 9. The load cell 7 has a fixed end 7b supported by a U-shaped arm 13 having rigidity, and the measuring end 7a flexes relative to the fixed end 7b due to a load acting on the measuring end 7a side. At this time, the strain gauge (not shown) detects the bending and outputs it as a continuous load signal. The drive mechanism 8 plays a role as the vibration control means of the present invention, and the rod 14 penetrating the sub chamber 10 from the arm 13 and protruding upward, and the rod 14
Is composed of an arm 13, a load cell 7, a jig 6, and a step motor 15 for driving up and down together with the sample A. Then, the load detected by the load cell 7 is input to the control and signal processing means 16.

The control and signal processing means 16 includes a drive mechanism 8
Is controlled, and the load detected by the load cell 7 is signal-processed according to a fixed procedure.
More specifically, for example, when the step motor 15 is intermittently driven by the driving mechanism 8 to reciprocate vertically on the jig 6 via the rod 14 at a constant cycle, when the jig 6 changes its direction, the load cell 7, the jig Vibration occurs in the system to be measured (vibration system) including 6 and sample A. The time variation of the vibration is as shown in FIG. 2, where W is the load detected by the load cell 7 and X is the displacement of the drive mechanism. Further, this vibration system can be represented by a simple vibration model as shown in FIG. 3, where Y is the displacement of the mass point, M is its mass, and k is the elastic modulus of the entire system. The solution of is that the angular velocity is ω, the initial amplitude value is A, the initial phase angle is α, the damping constant is n, the elastic modulus is k, and the time is t,

[Equation 1]

[Equation 2] Becomes On the other hand, since it is considered that the same relational expression holds for the waveform of the detected load W of the load cell 7, the angular velocity ω and the damping constant n can be obtained from the waveform of the load. As a specific configuration for that purpose, the control and signal processing means 16 obtains the angular velocity ω = 2π / T from the period T of vibration and also ^{obtains the} damping constant n from the reduction rate e ^−nt in one period T. It is configured. Also, this signal processing means 1
6 is configured to determine the mass M according to the equation (2) from the values of the angular velocity ω and the damping constant n described above, and the value of the elastic modulus k (preliminarily determined). Then, the value of M is in a wide range including the mass m of the sample A and the mass of the receiving frame 4 and the probe 6,
Since the masses of the receiving frame 4, the probe 6, and the like, which are components of the vibration system, hardly change during the processing, the temporal change of the mass M corresponds to the change of the mass m of the sample A as a result. Therefore, it is possible to measure a continuous change of only the mass m. In addition, in this device, since the buoyancy acting on the sample A, the gain and zero point of the load cell 7 and the differential pressure acting on the jig 6 are not affected in the measurement process, the influence of the buoyancy and the influence of the drift of the load cell 7 It becomes possible to perform measurement without such factors. Therefore, if dewaxing is performed using this apparatus, for example, it is possible to accurately detect the mass change of the sample A and control the dewaxing speed.

The present invention is not limited to the above-mentioned embodiments. For example, in the above embodiment, the drive mechanism 8 is provided with a triangular wave, but other than that, for example, a rectangular wave or a trapezoidal wave may be added. Also,
The spring 12 can be omitted if the elastic modulus of the probe 6 or the load cell 7 is appropriate. In addition, this device
It is also effective for the present inventor to use it in combination with a weight / displacement measuring device which is a dynamic measuring method proposed in Japanese Patent Application No. 3-63590. In that case, a support base for mounting the receiving frame is arranged at a position where the receiving frame is lowered. Furthermore, the device can also be used under weightlessness.

[0015]

Since the mass change measuring apparatus according to the present invention has the configuration described above, the mass change of the sample placed in a special atmosphere such as a furnace is affected by the influence of buoyancy due to the processing gas,
There is an effect that accurate measurement can be performed without being affected by the drift existing in the load cell itself.

[Brief description of drawings]

FIG. 1 is a diagram showing a heat treatment furnace to which a mass change measuring apparatus is applied according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a load W detected by a load cell during measurement and a displacement X of a mass point of a vibration system in the same example.

FIG. 3 is a diagram showing a model of the vibration system of the embodiment.

[Explanation of symbols]

 A ... Object to be measured (sample) 6 ... Jig 7 ... Load cell 8 ... Drive mechanism (excitation control means) 16 ... Control and signal processing means X ... Displacement of drive mechanism Y ... Displacement of mass point W ... Detected load

Claims (1)

[Claims] 1. A load cell for holding an object to be measured through a jig which is an elastic body, a vibration control means for intermittently exciting the object to be measured, and this vibration control means excites the object to be measured. A mass change measuring device characterized by comprising a signal processing means for detecting a vibration waveform of a load sometimes appearing in the load cell and calculating the mass of the object to be measured from its cycle T and a damping constant n.