Apparatus and method for evaluating hardness using piezoelectric elements

Abstract

The degree of hardness of an object can be measured using a piezoelectric element by converting it into a change in gas pressure. [Solution] The device comprises a flexible member 2 with gas sealed inside, a contact 1 which generates a voltage when the flexible member is pressed from the outside, causing a change in the pressure of the gas inside, and a corresponding piezoelectric element 6 which deforms in response to this pressure change, and a table which has a predetermined relationship between the degree of hardness of an object and the magnitude of the generated voltage, and the hardness of the object is evaluated by pressing the flexible member against the object with a constant pressure for a predetermined time and referring to the voltage generated from the contact 1 and the table.

Description

Technical Field

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[0001] The present invention relates to a hardness evaluation apparatus and a hardness evaluation method using a piezoelectric element, which apply a force to an object such as a fruit and evaluate the hardness of the object from the reaction force generated in the object at that time.

Background Art

[0002] In the case of products such as fruits that become soft over time, deteriorate in quality, and decrease in commercial value, or those that are originally damaged and soft, it is a general criterion to inspect the degree of hardness of the product before shipping. However, it is difficult to make a quantitative judgment because manually examining the hardness by hand is likely to be arbitrary. Therefore, as a method for inspecting the hardness of articles such as fruits, for example, there is known a method of lightly tapping at least one place of the article (tapping), resonating at the natural frequency, detecting the vibration signal generated at that time, and measuring the degree of hardness (see, for example, Patent Document 1). Also, there is known a method of measuring the hardness of an object by pressing a contactor against the object, measuring the reaction force, and measuring the reaction force per unit area from the measured value and the contact area of the contactor during pressing (see, for example, Patent Document 2). <000​​​​​​​​​​​​​​​​Special Publication No. 2003-506682 [Patent Document 2] Japanese Patent Publication No. 2006-250633 [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem we are trying to solve is that extracting a signal to measure the hardness of an object requires the use of special measurement methods and calculation techniques, which necessitates complex processing. [Means for solving the problem]

[0006] The most important feature of this invention is that, in order to measure the hardness of an object as the magnitude of the reaction force to pressure, the magnitude of the reaction force due to pressure is measured as a change in the pressure of a sealed gas, and this pressure change is detected by a piezoelectric element. [Effects of the Invention]

[0007] The present invention provides a hardness evaluation device and hardness evaluation method using a piezoelectric element, which allows the degree of hardness of an object to be determined by referring to the output voltage of the piezoelectric element and a table that defines the relationship between the output voltage and hardness in advance. This configuration has the advantage of being simple to implement and facilitating the sorting process of objects. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the operating principle of the contactor according to the present invention. [Figure 2] This is a diagram illustrating the contents of a table according to the present invention. [Figure 3] This figure illustrates another embodiment of the evaluation device according to the present invention. [Modes for carrying out the invention]

[0009] The objective of evaluating objects such as fruits for sorting purposes by examining their hardness was achieved with a simple configuration using a piezoelectric element and gas pressure changes. Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Examples]

[0010] Figure 1 is a diagram illustrating the operating principle of a contactor according to the present invention, where 1 is the contactor, 2 is a flexible cylindrical tube filled with a gas such as air, 3 is a detection unit that detects the pressure of the gas inside tube 2, 4 is a connection unit that connects tube 2 and detection unit 3, 5 is a gas introduction unit located inside detection unit 3 that guides the gas from tube 2 to the piezoelectric element, 6 is a piezoelectric element, and 7 is a substrate integrally connected to the piezoelectric element 6.

[0011] Tube 2 is made of a flexible, pliable material such as plastic resin, has a hollow interior filled with a gas such as air at a predetermined pressure, and is closed at one end. It is known that the higher the internal pressure, the higher the sensitivity to external forces applied to Tube 2, so the gas pressure is adjusted to achieve the required sensitivity. The length and diameter of Tube 2 can be changed depending on the measurement location. The gas inside Tube 2 acts on the piezoelectric element 6 via a connection part 4 connected to one end and a gas introduction part 4 in the detection unit 3. The piezoelectric element 6, together with the integrated substrate 7, is pressed downwards in the figure as the gas pressure increases, and a voltage is generated from the substrate 7 due to the piezoelectric effect associated with the deformation and vibration of the piezoelectric element 6. Thus, the amount of deformation of the piezoelectric element 6 and the substrate 7 is proportional to the magnitude of the gas pressure fluctuation, and a voltage corresponding to the amount of deformation is generated from the substrate 7, resulting in a voltage that is proportional to the magnitude of the pressure applied to the tube 2.

[0012] Figure 2 is a diagram illustrating the contents of a table according to the present invention, and in the figure, 8 shows the specific recording state of the table. For example, when evaluating the hardness of fruits such as apples, it is necessary to create a separate table (Table 8) for each type of fruit beforehand. Table 8 shows the output voltage from the piezoelectric element 6 in relation to the deformation (change in gas pressure) of tube 2 when a constant force applied during the evaluation is applied to the entire tube 2, using the tube 2 used in the actual evaluation. This deformation corresponds to the degree of stiffness. In other words, if the reaction force from the object is small, the deformation is small and the output voltage is also small, the object is judged to be soft. As the reaction force increases and the deformation increases, the object is judged to be hard.

[0013] Therefore, for each type of fruit, such as apples, an acceptable degree of hardness, i.e., an acceptable range of output voltage, is set in advance. This makes it possible to select only fruits with a certain level of hardness, and to remove the rest as defective products. Furthermore, since evaluation becomes difficult if the deformation of tube 2 (change in gas pressure) is small, in practical terms, the shape of tube 2 used and the constant force applied during evaluation must be configured appropriately so that evaluation is possible depending on the object. Also, the contents of Table 8 must be revised when the length, shape, etc., of tube 2 used are changed.

[0014] To perform a specific evaluation of the object, first, the entire tube 2 of the contactor 1 is brought into contact with the object, and then a constant pressure is applied to the entire tube 2 for a predetermined time, and the voltage output at that time is measured. The output voltage value is then compared (referenced) to the voltage value in Table 8, which is pre-recorded for the object in question. If the voltage value is within the set tolerance range, the object is evaluated as having appropriate hardness. In other words, a voltage equivalent to the sum of the reaction forces on the tube 2 is generated from the piezoelectric element over the entire length of the tube 2 in contact with the object, and the degree of hardness is evaluated. The allowable range can be determined according to the type of the object, etc. In the case of fruits, the degree of ripeness and the degree of hardness in case of damage, etc. are converted into voltage values to set the range of voltage values that can be tolerated. The conversion of the hardness into a voltage value can be obtained by measuring in advance the voltage value output for fruits with tolerable hardness.

[0015] Here, the predetermined time is the time when the object does not break when a certain pressure is continuously applied to the object. However, for example, there may be a case where the surface is soft and the inside is hard. When it is desired to evaluate based on the surface state, it is necessary to shorten the time for applying the pressure so that the contact 1 does not reach the inside of the object. Also, in the above embodiment, it was described as a configuration in which the entire tube 2 is brought into contact with the object. However, it is also possible to adopt a configuration in which only a part of the tube 2 is brought into contact to apply pressure, and the table 8 is also configured to record the contact of a part of the tube 2. Since the tube 2 is flexible, it has the advantage that it can be deformed into an arbitrary shape to evaluate the hardness.

[0016] FIG. 3 is a diagram for explaining another embodiment of the evaluation apparatus according to the present invention. In the figure, 9 and 10 are slide doors that open and close left and right when passengers board and alight from a railway vehicle, 11 and 12 are rubber members attached to the opening and closing ends of the slide doors 9 and 10, 13 and 14 are flexible members (cylindrical tubes) of the same length in which gas is enclosed inside the contactors according to the present invention, and 15 is a detection unit incorporating a piezoelectric element connected to the flexible members 13 and 14, respectively. The flexible members 13 and 14 extend from top to bottom along the edges of the slide doors 9 and 10 and are configured to be inserted inside the rubber members 11 and 12. They have the same length and are configured as cylindrical tubes of the same shape so that the sensitivities are the same. While the slide doors 9 and 10 are closed, the rubber members 11 and 12 are pressed against each other with a predetermined pressure.

[0017] Conventionally, a piezoelectric material was inserted inside rubber members 11 and 12. When a foreign object was sandwiched by a passenger's body or carried items as the slide doors 9 and 10 were opened and closed, the piezoelectric material converted the deformation of the rubber members 11 and 12 into an electrical signal and output it as an alarm. Automatically or when the crew noticed the abnormality and performed an operation to open the slide doors 9 and 10. However, the rubber members 11 and 12 are easily damaged or worn by foreign objects, etc. Therefore, even when a foreign object is sandwiched, the recognition by the piezoelectric material may become impossible, or the replacement of the expensive piezoelectric material may be required, etc., and maintenance work has occurred frequently.

[0018] By adopting the evaluation device according to the present invention, the cylindrical tubes 13 and 14 inserted inside the rubber members 11 and 12 themselves are deformed at some locations by pressing together with the members 11 and 12, and the sandwiching of a foreign object can be detected, and it is less affected by the damage or wear of the rubber members 11 and 12. Also, not only the presence or absence of sandwiching can be detected, but also the hardness of the foreign object sandwiched can be detected corresponding to the magnitude of the output voltage. Thereby, for example, when a passenger's body is sandwiched between the slide doors 9 and 10, etc., the urgency can be notified. The detection unit 15 is connected to the tubes 13 and 14 respectively, obtains the average value of the voltage generated by a piezoelectric element (not shown) from the change in each gas pressure, and compares and refers to the voltage value in a previously prepared table to detect the hardness of the foreign object. Note that the gases in the tubes 13 and 14 can be made into one, and it can also be configured to compare and refer to the output voltage from one piezoelectric element.

Industrial Applicability

[0019] The invention is not limited to the embodiments described above. The contactor can be made portable and configured to clamp onto an object to evaluate its hardness. It can also be made of a flexible material of a different shape instead of a tube. In the field of medical care, for example, the tube can be placed under the pillow or on the bed to examine the body movements of a patient lying in bed, and the magnitude and frequency of the output voltage can be used to monitor abnormalities in the patient, such as respiration and pulse. [Explanation of Symbols]

[0020] 1 Contactor 2, 13, 14 tubes 3.15 Detection Unit 4 Connection part 5. Gas introduction section 6. Piezoelectric element 7 circuit boards 8 tables 9, 10 Sliding doors 11, 12 Rubber components

Claims

1. A hardness evaluation device using a piezoelectric element, comprising a contact made of a flexible member with gas sealed inside, wherein when the flexible member is pressed from the outside, the pressure of the internal gas changes, and a piezoelectric element provided in response to this pressure change deforms and generates a voltage, and a table that has a predetermined relationship between the degree of hardness of an object and the magnitude of the generated voltage, wherein the hardness of an object is evaluated by pressing the flexible member against the object with a constant pressure for a predetermined time and referring to the voltage generated from the contact and the table.

2. The hardness evaluation apparatus using a piezoelectric element according to claim 1, characterized in that the contactor is composed of a plurality of contactors, each of which is made of a flexible, tubular member of the same length and shape with a gas sealed inside, and the piezoelectric element is provided at one end thereof so as to be in contact with the gas inside.

3. The hardness evaluation device using a piezoelectric element according to claim 2, characterized in that the contactor, which is composed of the tubular flexible member, is positioned in the opening and closing part of a sliding passenger door of a railway vehicle.

4. The hardness evaluation apparatus using a piezoelectric element according to claim 2, characterized in that the voltages generated from the plurality of contacts are configured such that the respective voltage values ​​are averaged and referenced with the table.

5. The hardness evaluation apparatus using a piezoelectric element according to claim 1, characterized in that the table is created for each type of object, and an acceptable range for evaluation according to the hardness of the voltage generated from the piezoelectric element in response to the applied pressure is set.

6. A method for evaluating hardness, comprising: pressing a contact made of a flexible material with gas sealed inside onto an object at a constant pressure for a predetermined time; causing a piezoelectric element provided in response to the pressure change of the internal gas to deform and generate a voltage; and evaluating the hardness of the object based on the relationship between a predetermined degree of hardness of the object and the magnitude of the generated voltage.

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