JPH071194B2 - Weight detector - Google Patents

Description

The present invention relates to a field relating to a scale for measuring the weight of an object, or to detect the weight of an object and use the weight information to improve the function and performance. The present invention relates to a weight detection function application device. For example, there is a heating and cooking device that effectively uses the weight information, and the weight of food in the heating chamber is automatically measured and the optimum heating time, heating output, heating pattern, etc. are automatically determined according to the weight, and the cooking performance is improved. Has been applied to improve.

2. Description of the Related Art Heating cookers equipped with a weight detection function that detects the weight of food and controls heating are already known, and are widely applied in the field of cooking automation represented by automatic thawing, especially in microwave ovens. Has been done. A conventional general weight detection device includes a load transmission mechanism called a Roberval mechanism. The Roberval mechanism is a parallelogram mechanism that is widely used in the basic structure of a balance to prevent tilting of the platform of the scale and cause an error due to the placement position (error caused by the placement position on the load tray,
Hereinafter referred to as a position error. ) Has been used to eliminate. However, in order to meet the recent demand for smaller, lighter and lower cost components in the market, a weight detection device without the above-described Roberval mechanism has been devised. (Japanese Patent Application No. 62-59382) FIG. 6 shows a cross-sectional view of a main part of a microwave oven equipped with a weight detection device in which the conventional Roberval mechanism is omitted. The load of the food transmitted by the support rotary shaft 5 is transmitted to the load transmission means 3 by pressing the leaf springs 2 whose both ends are fixed. The leaf spring 2 is a mechanism for reducing noise due to wear and vibration of the load transmitting means 3 due to the rotation and sliding of the motor 4.

Problems to be Solved by the Invention However, in the weight detection device having such a configuration,
The support rotary shaft 5 is held in the vertical direction by bearings 6 and 7, and the load is transmitted in the thrust direction of the support rotary shaft 5, but the support rotary shaft 5 depends on the clearance between the shaft and the bearing.
The transmission loss of load caused by the inclination of is unavoidable.
FIG. 7 is an explanatory diagram showing changes in load transmission due to the inclination of the support shaft 5. During the measurement, the inclination of the support rotary shaft 5 changes variously on a case-by-case basis, and as shown in FIG. 7 (a), the load F (real arrow) may be accurately transmitted in the vertical direction. As shown in FIG. 7 (b), the support rotary shaft 5 tilts,
In some cases, the contact point between the load transmitting means 3 and the leaf spring 2 is shifted to the point A, and the load transmitting component is attenuated to Fcosα (dotted arrow line). Thus, it is considered that the state of the support rotary shaft 5 is changing sequentially. FIG. 8 shows the instantaneous value of the output of the load detecting means 16 while the motor is rotating. In this way, the weight greatly changes depending on the rotational position, and the measured value greatly varies depending on the timing at which the data is detected. Therefore,
In order to obtain more accurate data, it is necessary to integrate and average the outputs from the weight detection device for a certain period. When this pulsation becomes large, a long time integration is required to measure accurate data, and the measurement time becomes long. In the weight detection device equipped with the Roberval mechanism, the measurement can be performed instantaneously and the cooking time can be displayed to the user immediately, but the usability is significantly deteriorated. On the contrary, if you place importance on usability and measure for a short time, the error will increase accordingly,
This causes inconvenience in cooking performance.

The present invention solves such a conventional problem, and provides a highly accurate weight detection device with a simple structure that reduces a load transmission error caused by a clearance between a supporting rotary shaft and a bearing.

Means for Solving Problems The weight detection device of the present invention includes a mounting table on which an object to be measured is mounted, load detecting means for detecting a load, and a predetermined amount of movement in a supporting direction supporting the mounting table. A free support rotary shaft, a rotation drive means for rotationally driving the support rotary shaft, an elastic body that supports the support rotary shaft and is movable with elastic force in the thrust direction of the support rotary shaft, and a support rotary shaft that supports the elastic body. In a weight detecting device including a mounting table and a load transmitting means for transmitting a load of an object to be measured to the load detecting means, a portion of the load transmitting means that comes into contact with the elastic body has a planar shape.

In the weight detecting device of the present invention, since the contact portion between the load transmitting means and the elastic body is flat, the contact point between the elastic body and the supporting rotary shaft is displaced during rotation due to the clearance of the supporting rotary shaft. Even if the point where the body presses the load transmitting means moves, the load transmitting means is accurately pressed in the vertical direction, and the load is transmitted to the load detecting means without loss. As a result, the pulsation width of the detected weight during rotation is significantly reduced, so that the integration time required for averaging the data can be shortened and an accurate weight can be detected in a short time. It is desirable that the end surface of the support rotary shaft that contacts the elastic body be sharpened so that the contact shift does not move much from the design center.

Example Hereinafter, a weight detection device of the present invention will be described with reference to the drawings. FIG. 2 is an external perspective view of a microwave oven with a weight detecting function equipped with the weight detecting device of the present invention. A door 9 that can be opened and closed is pivotally supported on the front surface of the main body 8, and a key input unit 11 for selecting a type of cooking and setting a cooking time is provided on an operation panel 10 and a user monitors the operating state, or A display tube 12 for interaction is provided. FIG. 3 is a system block diagram of a microwave oven with a weight detection function. In addition, 13 is a heating chamber, 14 is food, and 15 is a mounting table for mounting food, which is rotationally driven by a motor to improve heating unevenness due to radio wave distribution. Reference numeral 16 is a load detecting means which receives the load of the food 14 and converts it into an electric signal. Reference numeral 18 denotes an interface circuit with the microcomputer 17, which converts the electric signal into a signal detectable by the microcomputer 17. The microcomputer 17 calculates the weight by performing a predetermined calculation from the signal. 19 is a magnetron for supplying high frequency power into the heating chamber 13, 20 is a high voltage generating circuit for driving the magnetron for driving the magnetron 19, 21 is a commercial power source, 22 is for turning on / off the power supply to the magnetron 19. It is a relay actuator.

Therefore, the user selects the cooking menu from the key input unit 11, the microcomputer 17 detects the weight of the food, and further performs a predetermined calculation from the weight information to automatically prepare the cooking time, cooking process, and heating pattern. To decide. The weight detection device has been used in such an application in a microwave oven, and is now a very general function.

FIG. 1 shows a cross-sectional view of a main part of a weight detecting device according to an embodiment of the present invention. 4 is a motor for rotating the mounting table 15, 5
The supporting rotary shaft supports the mounting table 14, and the bearing 6 and the shaft support 7 vertically support the mounting table 14. Further, each contact portion is provided with an appropriate clearance, and in some cases, a lubricating oil or the like is applied to improve wear and slidability. The motor 4 is a synchronous motor composed of a permanent magnet and a coil, and rotates in synchronization with the cycle of the power supply. Furthermore, low speed and high torque are achieved by using multiple gears such as gears 23 and 24. In addition, the support rotary shaft 5
A through hole is provided in the shaft and a shaft stopper pin 25 is inserted to prevent the shaft from falling off. The load W of the mounting table 15 and the food 14 is transmitted through the support rotary shaft 5 in the thrust direction of the shaft.
This load W is transmitted to the load transmitting means 3 mounted on the load detecting means 16 via the leaf springs 2 whose both ends are fixed. This is to prevent the load transmitting means 3 from being worn by the sliding of the supporting rotary shaft 5, and the load detecting means 16
It is a leaf spring with a weak elasticity that does not affect the characteristics of. A configuration diagram of the load detection means 16 is shown in FIG. 26
Is an alumina ceramic diaphragm, and 28 is a gold electrode printed on the surfaces of the diaphragms 26 and 27, which is a thin film of several microns. Reference numeral 29 is a glass seal, which has a minute gap of several tens of microns, and two diaphragms 26 and 27 are opposed to each other to electrically form a capacitor. Here, when a load is applied to the diaphragm 26, the diaphragm 26
26 bends and the gap between the electrodes narrows, so the capacitance changes. Generally, in the case of a parallel plate electrode, the theoretical formula of the electrostatic capacitance C is S, where the electrode area is S, the interelectrode gap is d, and the interelectrode dielectric constant is ε. Therefore, also in this case, the configuration is almost the same, and when the load is applied, the inter-electrode gap d becomes small and the electrostatic capacitance C becomes large. The load transmission means 3 is a diaphragm 26.
It has a function of transmitting a point load of a constant pressurizing area defined by the contact area with the diaphragm 26 to the load detecting means 3. The capacitance of the load detecting means 16 is guided to the interface circuit 18 by the lead wire 30. The interface circuit 18 is composed of an astable multivibrator, and the frequency changes depending on the capacitance. The microcomputer 17 detects the frequency by counting the number of pulses from the interface circuit 18 for a certain period of time, and further performs a predetermined calculation (for example, a conversion formula expressing the relationship between frequency and weight by power series approximation). Go and find the weight.

As described above, in the case of the present weight detection device, since the Roberval mechanism is omitted, the structure is very compact, but the position error is disadvantageous. As shown in FIG. 1, the bearings 26, 2 of which the rotary shaft 5 is held in the vertical direction by the bearings 26, 27.
Due to the clearance between 7 and the supporting rotary shaft 5, the supporting rotary shaft 5 is inclined, and the point at which the load transmission means 3 is pressed is during rotation
It changes sequentially depending on where the food is placed. However, in the weight detecting device of the present invention, since the structure of the portion of the load transmitting means 3 that comes into contact with the leaf spring 2 is processed into a flat surface, the weight transmitting means 3 is always in the vertical direction even if the pressing point moves. It has a structure that force is applied to and no loss occurs during transmission. FIG. 8 shows the difference in measurement depending on the structure of the load transmitting means 3. FIG. 8 (a) shows the case where the load transmitting means is spherical, and FIG. 8 (b) shows the case where the load transmitting means is flat, and the amplitude is remarkably reduced. Now, consider the case of integrating and averaging instantaneous data in order to average the data. As a simple model, the instantaneous value of the frequency is a sine wave having a center frequency ₀ , an amplitude A, and an angular velocity (motor speed) ω, as shown in FIG. The frequency of the time-integrated average with initial time t ₀ and integration time t ₁ is The error from the true value ₀ is proportional to the amplitude A and inversely proportional to the integration time t ₁ . Therefore, it can be seen that the error is reduced by reducing the amplitude. As shown in FIG. 8, even if the waveform is slightly distorted, it is very advantageous to similarly reduce the fluctuation range in order to improve the measurement accuracy. Further, if a certain degree of error is allowed, the integrated average time, that is, the time required for measurement can be shortened. This specific integration and averaging operation can be easily realized by counting the number of pulses output from the interface circuit 18 in the integration time and dividing the counted number by the integration time.

EFFECTS OF THE INVENTION As described above, in the weight detection device of the present invention, the structure of the contact portion of the load transmission means with the elastic body is a flat surface, and the support rotation shaft is inclined due to the clearance between the support rotation shaft and the bearing portion. However, the load is accurately transmitted in the vertical direction to the load transmitting means. Therefore, since the fluctuation range of the measured value during rotation is significantly reduced, the integration time required for averaging is short, and the weight can be detected more quickly than before. Since the rotation cycle of the motor used in the current microwave oven is as long as 10 to 12 seconds, it is very advantageous to shorten the integration time in order to improve usability.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part of a weight detecting device according to an embodiment of the present invention, FIG. 2 is a perspective view of the main body, FIG. 3 is a block diagram of the system, and FIG. 4 is an exploded view of the load detecting means. FIG. 5 is a perspective view, FIG. 5 is an explanatory view of the principle of integral averaging, FIG. 6 is an enlarged cross-sectional view of a main part of a conventional weight detection device, and FIG. 7 is an operation explanatory view of load transmission loss due to the inclination of the supporting rotary shaft. FIG. 8 is an output waveform diagram showing the difference in output due to the structural difference of the load transmitting means. 2 ... leaf spring, 3 ... load transmission means, 4 ... motor,
5: Support rotation axis, 15: Mounting table, 16: Load detection means.

Claims (1)

[Claims] 1. A mounting table for mounting an object to be measured, a load detecting means for receiving a load and outputting an electrical physical quantity corresponding to the load, a supporting table for supporting the mounting table, and a predetermined displacement in a supporting direction. A rotatable support rotation shaft, a rotation drive means for rotationally driving the support rotation shaft, an elastic body that receives the support rotation shaft and displaces in the support direction, and the load detection means that receives the elastic body. And a load transmitting means for transmitting a load to the elastic body, wherein the load transmitting means has a flat contact portion with the elastic body.