Surface temperature sensor

Abstract

Provided is a surface temperature sensor that achieves high temperature measurement accuracy with good responsiveness using a simple mechanism.　The surface temperature sensor detects the temperature of the surface of a temperature measurement target object. The temperature sensor includes a holder made of resin in which a pair of metal lead frames are insert-molded, and a temperature-sensitive element which is attached across and electrically connected to the tips of respective extension portions of the pair of lead frames protruding from the holder. When the temperature-sensitive element is disposed on the surface of the temperature measurement target object and the holder is moved toward the surface, the extension portions are elastically deformed so as to press the temperature-sensitive element onto the surface while the distance between the surface and the holder is regulated to a constant value by a regulation member.

Description

Surface temperature sensor

[0001] The present invention relates to a surface temperature sensor for detecting the temperature of a heater surface, and in particular to a surface temperature sensor using a thermistor for detecting the surface temperature of a ceramic heater in a heat fixing unit.

[0002] In order to control the surface temperature of a ceramic heater of a heat fixing unit such as a printer or a copying machine, a surface temperature sensor that detects a surface temperature by bringing a temperature sensitive element into contact with the heater surface is known.

[0003] For example, Patent Document 1 discloses a surface temperature sensor that detects the surface temperature of a heating body by pressing a heat-resistant elastic body having a temperature sensitive element provided on a lower surface (bottom surface) against the surface of the heating body with a spring. Here, regarding a conductive member that provides electrical connection to the temperature sensitive element, insert molding is performed such that a portion other than a welded portion to which a covered conductive wire is attached is embedded inside the heat-resistant elastic body, thereby suppressing heat radiation, accelerating the temperature rise of the temperature detecting element, and speeding up the responsiveness of temperature detection. It is stated that by adopting such a structure, stabilization of fixing performance, reduction of power consumption, and improvement of reliability of a heat fixing device / image forming apparatus can be achieved.

[0004] Japanese Patent Application Laid-Open No. 2002-122489

[0005] As described above, there is a need for a surface temperature sensor that can reduce the heat capacity of the surface temperature sensor, improve the stability of contact with the surface of a temperature measurement object, and achieve high temperature measurement accuracy with good responsiveness. On the other hand, a simple mechanism is also required.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface temperature sensor that can achieve high temperature measurement accuracy with good responsiveness while having a simple mechanism.

[0007] The surface temperature sensor according to the present invention is a surface temperature sensor for detecting the surface temperature of an object to be measured, and comprises a resin holder from which a pair of metal lead frames are insert-molded, and a temperature sensing element attached across the tips of the respective extensions of the pair of lead frames protruding from the holder and electrically connected, wherein when the temperature sensing element is placed on the surface of the object to be measured and the holder is moved toward the surface, the extensions elastically deform to press the temperature sensing element onto the surface, while a regulating member is provided to restrict the distance between the surface and the holder to a certain value.

[0008] With these features, the elastic deformation of the extended portion is restricted to a certain range by the restricting member, thereby protecting the extended portion, and the distance between the holder and the surface of the object to be measured is maintained at a constant value, thereby improving the stability of contact between the surface and the temperature sensing element.

[0009] In the invention described above, the temperature sensing element may be plate-shaped, and the main surface of the plate-shaped element may be attached to the extensions near both ends so that the angle of the plate-shaped main surface is variable with respect to the holder. With this feature, the angle of the main surface of the plate-shaped temperature sensing element with respect to the holder can be changed so that it follows the surface of the object to be measured, thereby further improving the stability of contact between the surface of the object to be measured and the temperature sensing element.

[0010] In the invention described above, the extension may be characterized by bending and extending from the side of the line segment connecting the two ends of the temperature-sensing element to hold the temperature-sensing element. With this feature, the angle of the main surface of the plate-shaped temperature-sensing element can be easily varied with respect to the holder, and the stability of contact with the surface of the object to be measured can be improved.

[0011] In the invention described above, the restricting members may be provided in pairs on both outer sides of the pair of extensions. With this feature, the distance between the surface and the holder can be restricted to a certain value with a simple structure, and the angle of the holder in the direction of the line segment connecting the restricting members can be stabilized with respect to the surface of the object to be measured, thereby improving the stability of contact with the surface of the object to be measured.

[0012] In the invention described above, the extension may be characterized by bending and extending from the side of the line segment connecting the pair of regulating members to hold the temperature sensing element. With this feature, the main surface of the temperature sensing element can be stabilized in the direction of the line segment and followed by the surface of the object to be measured toward its side, thereby increasing the stability of contact with the surface of the object to be measured.

[0013] In the above-described invention, an insulating film may be provided covering the temperature-sensing element, and the insulating film may be interposed between the temperature-sensing element and the surface of the object to be measured. Alternatively, the insulating film may be in contact with the temperature-sensing element without containing any adhesive components. With such features, it is possible to ensure insulation from the surface of the object to be measured using an insulating film with a relatively small heat capacity, while maintaining a high level of stability in contact with the surface of the object to be measured.

[0014] This is a perspective view of a surface temperature sensor according to one embodiment of the present invention, showing (a) a state with an insulating film attached and (b) a state with the insulating film removed. This is a side view of the surface temperature sensor showing (a) a state without load applied and (b) a state pressed against an object to measure temperature. This is a front view of the main part of the surface temperature sensor showing (a) a state without load applied and (b) a state pressed against an object to measure temperature. This is a perspective view of the temperature sensing element used in the surface temperature sensor. This is a graph showing the simulation results of the relationship between load and stress applied to the extended portion. This is a side view of the main part of a surface temperature sensor according to another embodiment.

[0015] Hereinafter, an embodiment of the surface temperature sensor of the present invention will be described with reference to Figures 1 to 4. In each figure, the scale of each component has been appropriately changed for explanatory purposes in order to make each component recognizable. Also, the same or equivalent parts are denoted by the same reference numerals, and redundant explanations are omitted.

[0016] <First Embodiment> The first embodiment will be described with reference to Figures 1 and 2. Figure 1(a) is a perspective view showing the surface temperature sensor according to the first embodiment with an insulating film attached, and Figure 1(b) is a perspective view showing the surface temperature sensor with the insulating film removed. Figure 2 is a side view of the surface temperature sensor, and Figure 2(b) shows the sensor in contact with an object whose temperature is to be measured.

[0017] As shown in Figures 1 and 2, the surface temperature sensor 1 is a sensor that detects the surface temperature of an object S to be measured. It comprises a holder 2 that forms the main body, which is a horizontally elongated, roughly rectangular parallelepiped with a plurality of recesses, a metal lead frame 3 for electrical connection, and a temperature sensing element 10. The direction of the holder 2 is defined as +y in the direction to the right of the paper, the direction of the side that contacts the object S to be measured (upper side in Figure 1, lower side in Figure 2) is +z, and the direction perpendicular to these, towards the back of the paper in Figures 1 and 2, is +x.

[0018] The holder 2 is formed using a resin material that has heat resistance and insulating properties. For example, LCP resin (liquid crystal polymer) can be suitably used as the material for such a resin holder 2, but PPS resin (polyphenylene sulfide resin) or PEEK resin (polyether ether ketone resin) may also be used. The holder 2 has an opening 21, which is one of its recesses, formed approximately in the center of its longitudinal direction. The opening 21 is used, for example, for alignment when attaching the surface temperature sensor 1 to an object to be measured, such as a heat fixing unit.

[0019] An insulating film 5 is attached to the side of the holder 2 in the -y direction from the opening 21, covering the surface facing the object to be measured S (the surface located in the z direction). The insulating film 5 is used as an interposition between the object to be measured S and the temperature sensing element 10 when electrical insulation is required, and can be attached by engaging the holes provided in the insulating film 5 with locking parts 24 that protrude from the holder 2 in the ±x directions. Inside the insulating film 5 (see Figure 1(b) in particular), there is a temperature sensing element 10, a pair of elastic frames 32 that hold it, and a pair of projections 23 spaced apart in the longitudinal direction of the holder 2. The projections 23 are substantially plate-shaped parts of the holder 2 provided on both outer sides of the pair of elastic frames 32, and are provided so as to protrude in the z direction with the normal of their main surface facing the longitudinal direction of the holder 2.

[0020] Furthermore, a pair of grooves 22 are formed on the other end of the holder 2 in the longitudinal direction (the end in the y-direction) on either side of the opening 21. The grooves 22 form recesses for arranging a pair of external lead wires, and the external lead wire connection portion 31, which is the end of the lead frame 3 described later, is positioned at the bottom of each recess to expose it. Specifically, the external lead wires can be insulated lead wires.

[0021] The lead frame 3 is embedded in the holder 2 by insert molding, with a portion of it exposed, and is fixed and held in place. The lead frame 3 is a plate-like body electrically connected to the temperature-sensing element 10 and a pair of external lead wires. The material of the lead frame 3 is preferably a conductive metal or alloy, which has a relatively high elastic limit in the operating temperature range (for example, around 175°C). Suitable materials for this purpose include, for example, heat-resistant spring stainless steel.

[0022] The lead frame 3 has an external lead wire connection portion 31 at one end and an elastic frame 32 at the other end. The elastic frame 32 is an extension of the lead frame 3 that extends from the lead-out portion 25 of the embedded holder 2. The elastic frame 32 plays a role in elastically holding the temperature sensing element 10 and is electrically connected to the temperature sensing element 10 via a pair of leads 4. The lead-out portion 25 is a plate-like portion that extends in the longitudinal direction of the holder 2 so as to fill the space between a pair of protrusions 23. The lead-out portion 25 has the lead frame 3 embedded inside and extends toward the object to be measured S, and the elastic frame 32, which is an extension of the lead frame 3, is exposed from its end, causing the elastic frame 32 to extend toward the object to be measured S.

[0023] A pair of elastic frames 32 hold a temperature-sensing element 10 between them. The temperature-sensing element 10 is electrically connected to the pair of elastic frames 32 by a lead 4 that straddles the tip of each frame and attaches near both ends. The lead 4 also mechanically holds the temperature-sensing element 10 near both ends, straddling the pair of elastic frames 32. The lead 4 can be made of a conductive material with relatively high mechanical strength, such as iron-based materials like Kovar, stainless steel, or nickel alloy. The lead 4 can be in the shape of a thin wire or a plate. Here, a thin wire with silver plating on a nickel base was used as the lead 4.

[0024] Referring to Figure 3, the elastic frame 32 includes a bent portion that bends from the direction toward the temperature-sensing element 10 (z-direction) toward the side, and extends from the side of the line segment connecting both ends of the temperature-sensing element 10 to hold the temperature-sensing element 10. More specifically, it is bent in a roughly L-shape when viewed from the y-direction. That is, the side is in the ±x direction, and in this embodiment, the side is in the -x direction. This direction is also perpendicular to the line segment connecting both sides of the lead 4 of the temperature-sensing element 10 to which it is connected. Furthermore, the bent tip of the elastic frame 32 is a flat contact surface 32a that extends in a plate-like manner and is connected to the temperature-sensing element 10 via the lead 4 at approximately its center. As a result, the temperature-sensing element 10 is positioned between the contact surfaces 32a of the pair of elastic frames 32, preferably approximately in the center.

[0025] Here, as shown in Figure (a), when no load is applied, the contact surface 32a is tilted so that the angle of its L-shape bend is obtuse. On the other hand, as shown in Figure (b), the surface temperature sensor 1 is moved closer to the surface of the object to be measured S and pressed with a force greater than the load that causes the elastic frame 32 to elastically deform. As a result, the elastic frame 32 elastically deforms to reduce the angle of the bent portion, and the contact surface 32a is positioned along the surface of the object to be measured S so that the temperature sensing element 10 is pressed against the object to be measured S. In other words, the extended portion of the elastic frame 32 elastically deforms so that the temperature sensing element 10 is pressed onto the surface of the object to be measured S. Furthermore, by elastically deforming the elastic frame 32 to change the angle of the bent portion, the angle of the main surface of the temperature sensing element 10 is made variable with respect to the holder 2. This allows the elastic frame 32 to elastically deform so that the main surface of the temperature sensing element 10 is positioned along the surface of the object to be measured S.

[0026] At this time, the surface temperature sensor 1 is positioned in the z direction by pressing the protrusions 23 located on both sides of the elastic frame 32 in the y direction against the surface of the object to be measured S. In other words, the protrusions 23 act as restricting members that limit the distance between the surface of the object to be measured S and the holder 2 to a certain value. Therefore, the amount of deflection of the elastic frame 32 is restricted to a certain level or less. By keeping this amount of deflection within the elastic limit of the elastic frame 32, the temperature sensing element 10 is pressed against the object to be measured S with a constant force, and that force is maintained. In other words, the protrusions 23 have the function of limiting the pressing force applied to the elastic frame 32 and preventing plastic deformation of the elastic frame 32. This increases the stability of the contact between the temperature sensing element 10 and the surface of the object to be measured S. In this embodiment, it is recommended that the pressing force on the elastic frame 32 be 180 gf.

[0027] In other words, the elastic frame 32 acts as a leaf spring that presses the temperature-sensing element 10 against the object to be measured S, forming an elastic mechanism for pressing the temperature-sensing element 10 against the object to be measured S. When the temperature-sensing element 10 is pressed against the object to be measured S with a constant load, the stability of contact is increased as described above, which can result in improved temperature measurement accuracy. Furthermore, since the temperature-sensing element 10 is directly connected to the elastic frame 32 via the lead 4, even if the relative position of the surface temperature sensor 1 and the object to be measured S shifts, the temperature-sensing element 10 can follow the object to be measured S in accordance with the shift, preventing malfunctions during temperature measurement (such as loss of temperature data). Note that the surface of the object to be measured S is assumed to be flat. If the shape is other than flat, the protrusion dimensions of the projection 23 can be designed to match the shape, so that the temperature-sensing element 10 is pressed against it in the same way.

[0028] As described above, the projection 23 contacts the surface of the object S to be measured when the elastic frame 32 is brought into contact with the object S. This allows the elastic frame 32 to elastically deform within its elastic limit while contacting the surface of the object S, without undergoing plastic deformation. By preventing plastic deformation in this way, the elastic mechanism when the temperature sensing element 10 is brought into contact with the object S is prevented from being lost. Thus, although it is a simple mechanism of bending the lead frame 3 to form the elastic frame 32 and providing the projection 23 which acts as a regulating member, it is possible to improve the stability of contact with the surface of the object S to be measured. As a result, the surface temperature sensor 1 can obtain high temperature measurement accuracy with good responsiveness.

[0029] In particular, the elastic frame 32 extends its contact surface 32a, which is the bent portion at its tip, laterally (in the x-axis direction) along the line segment (in the y-axis direction) connecting the pair of projections 23, which are regulating members. That is, the contact surface 32a extends perpendicular to the line segment connecting the pair of projections 23. Furthermore, the elastic frame 32 has a variable angle at the bent tip of its contact surface 32a so that it follows the surface of the object to be measured S, and the angle of the main surface of the temperature sensing element 10 is also variable accordingly. In other words, the inclination of the main surface of the temperature sensing element 10 is automatically adjusted by the contact surface 32a so that the inclination in the x-direction matches the surface of the object to be measured S. In addition, the projections 23 are positioned so that the line segment connecting their tips follows the surface of the object to be measured S. As a result, the inclination in the y-direction of the contact surface 32a of the elastic frame 32 and the main surface of the temperature sensing element 10 are positioned to match the surface of the object to be measured S. In other words, the inclination of the main surface of the temperature sensing element 10 is automatically adjusted in the x and y directions to match the surface of the object S whose temperature is being measured, thereby aligning the main surface directly with the surface and, as a result, further improving the stability of contact with the surface of the object S whose temperature is being measured.

[0030] Furthermore, it is preferable that the projection 23 be positioned at a distance of a certain value or more from the temperature sensing element 10 so as not to lower the temperature of the temperature sensing part of the object S in contact with the temperature sensing element 10, that is, to reduce the heat flow from the temperature sensing part to the holder 2. This can improve the accuracy of temperature measurement. Note that three or more projections 23 may also be provided.

[0031] The plate-shaped pair of lead frames 3 are arranged side-by-side within the holder 2 in a yz plane aligned with the x-direction. They extend from the lead portion 25, which includes this plane, as an elastic frame 32 and are bent in the -x direction. This allows the x-direction dimension (thickness) of the surface temperature sensor 1 to be relatively small. As a result, the amount of heat flowing from the object S to be measured to the holder 2 can be suppressed, contributing to improved temperature measurement accuracy.

[0032] In the surface temperature sensor 1, as described above, an insulating film 5 may be provided so that the temperature sensing element 10 and the object to be measured S are electrically insulated. The method of fixing the insulating film 5 is not particularly limited, but it can be fixed by providing a locking portion 24 for fixing the insulating film 5 to the holder 2. Alternatively, it is preferable to use a method that does not provide an adhesive component between the temperature sensing element 10 and the insulating film 5, such as by heat-pressing the overlapping portion of the insulating film 5 to the holder 2, in order to achieve good responsiveness.

[0033] The temperature-sensing element 10 will be described with reference to Figure 4. The temperature-sensing element 10 is a thermoresistive element, specifically a thin-film thermistor formed on an insulating substrate 11. The temperature-sensing element 10 comprises an insulating substrate 11, on which a temperature-sensing thin film 10a, a pair of electrode layers 12a and 12b, and a protective film 13 are formed. The insulating substrate 11 is substantially rectangular in shape, for example, having a main surface dimension of 1 mm in width and 0.5 mm in height, and is formed from a ceramic material or a glass material. The thickness of the insulating substrate 11 is 200 μm or less, preferably 150 μm or less.

[0034] The temperature-sensitive thin film 10a is a temperature-sensitive resistance thin film that functions as a temperature sensor, and is an NTC thermistor thin film made of an oxide semiconductor having a negative temperature coefficient. The thermistor thin film is formed on the insulating substrate 11 and on the electrode layers 12a and 12b by sputtering, so as to straddle the electrode layers 12a and 12b, and is electrically connected to the electrode layers 12a and 12b.

[0035] The thermistor thin film is composed of a thermistor material that mainly contains a composite metal oxide having a spinel structure, which is composed of two or more elements selected from transition metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe). Furthermore, minor components may be included to improve properties. The composition and content of the main and minor components can be appropriately determined according to the desired properties.

[0036] A pair of electrode layers 12a and 12b are formed on an insulating substrate 11, electrically connected to the temperature-sensing element 10, and arranged facing each other with a predetermined distance between them. Specifically, the pair of electrode layers 12a and 12b are thin metal films deposited by sputtering, and the metal material can be a precious metal such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), ruthenium (Ru), or their alloys, such as an Ag-Pd alloy. In this embodiment, the electrode layers 12a and 12b are formed beneath the temperature-sensing thin film 10a, but they may also be formed on or within the temperature-sensing thin film 10a.

[0037] The protective film 13 covers the region where the temperature-sensitive thin film 10a is formed, and also covers the electrode layers 12a and 12b by forming an exposed portion so that at least a part of the electrode layers 12a and 12b is exposed. The protective film 13 can be formed by depositing silicon dioxide (SiO2), silicon nitride (Si3N4), etc. by sputtering, or by forming lead glass, borosilicate glass, lead borosilicate glass, etc. by printing.

[0038] <Relationship between load and stress applied to the elastic frame> Figure 5 is a graph showing the results of a simulation analysis of the load and stress applied to the elastic frame 32 when the surface temperature sensor 1 is pressed against the surface heater, which is the object to be measured. As simulation conditions, the material of the elastic frame 32 was set to SUS301-CSP-EH ("SUS" is a registered trademark), the distance between the surface heater and the protrusion 23 at zero load was set to 0.6 mm, and the load and stress were calculated as the elastic frame 32 was brought closer to the surface heater. Note that if the stress exceeds the yield strength of 1275 MPa (see line A), the elastic frame 32 will undergo plastic deformation.

[0039] From the figure, it can be seen that the elastic frame 32 undergoes plastic deformation at a load of around 300 gf, but the load applied when the projection 23 and the surface heater come into contact is approximately 280 gf (see line B). Therefore, the elastic frame 32 does not experience stress sufficient to undergo plastic deformation. In other words, it can be confirmed that the projection 23 restricts the movement of the elastic frame 32 and limits the pressure applied to it. In short, plastic deformation of the elastic frame 32 can be prevented.

[0040] <Second Embodiment> As shown in Figure 6, the shape of the elastic frame 32 and the arrangement of the protrusions 23 can also be changed. In detail, the elastic frame 32, which is an extension of the lead frame 3, extends from the lead-out portion 25 of the holder 2 and is a plate-like body having a width in the ±x direction (front-to-back direction of the paper). The pair of elastic frames 32 are substantially symmetrical with respect to the x-y plane passing through the center of the temperature-sensing element 10 on both sides of the temperature-sensing element 10 in the y-axis direction. The pair of elastic frames 32 extend in the +z direction while bending in a wave-like manner in the ±y direction from the lead-out portion 25, and then connect to the lead 4 via contact surfaces 32a that extend toward the temperature-sensing element 10 so as to be close to each other. In other words, the contact surfaces 32a extend in the direction of the line segment connecting the two sides of the lead 4 of the temperature-sensing element 10 to which it is connected.

[0041] On the other hand, the projections 23 are provided at three locations on the +y side, -y side, and +x side (back of the paper) of the temperature sensing element 10, and each projection has a vertex that protrudes in the +z direction, with the positions of each vertex positioned on the same x-y plane. In other words, the vertices of the three projections 23 are at the same height. These vertices are positioned at the corners of a triangle when viewed from the z-axis direction.

[0042] As shown in Figure (a), when no load is applied, the contact surface 32a is located on the +z side of the plane passing through the vertices of the three protrusions 23. On the other hand, as shown in Figure (b), when the surface temperature sensor 1 is pressed against the object S with a force greater than or equal to the load, the elastic frame 32 elastically deforms to reduce the angle of the wavy bent portion, causing the temperature sensing element 10 to press against the object S and positioning the contact surface 32a on the surface of the object S. At this time, the plane passing through the vertices of the protrusions 23 coincides with the surface of the object S. Therefore, the temperature sensing element 10 can be pressed against the surface of the object S with a constant load without changing the angle of the contact surface 32a and the temperature sensing element 10 connected thereto.

[0043] With this configuration, similarly to the first embodiment described above, the protruding portion 23 has a function of limiting the pressing force applied to the elastic frame 32 and prevents plastic deformation of the elastic frame 32. Thus, the stability of contact between the temperature-sensitive element 10 and the surface of the temperature measurement object S can be improved.

[0044] While embodiments according to the present invention and modified examples based thereon have been described so far, the present invention is not necessarily limited to these examples. Further, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the gist of the present invention or the scope of the appended claims.

[0045] 1 Surface temperature sensor 2 Holder 3 Lead frame 5 Insulating film 10 Temperature-sensitive element 23 Protruding portion 32 Elastic frame

Claims

1. A surface temperature sensor for detecting the surface temperature of an object to be measured, comprising: a resin holder formed by insert molding a pair of metal lead frames; and a temperature sensing element attached to the tips of the respective extensions of the pair of lead frames protruding from the holder and electrically connected, wherein when the temperature sensing element is placed on the surface of the object to be measured and the holder is moved toward the surface, the extensions elastically deform to press the temperature sensing element onto the surface, while a regulating member is provided to restrict the distance between the surface and the holder to a certain value.

2. The surface temperature sensor according to claim 1, characterized in that the temperature sensing element is plate-shaped and the main surface of the plate is attached to the extensions near both ends such that the angle of the plate-shaped main surface is variable with respect to the holder.

3. The surface temperature sensor according to claim 2, characterized in that the extension extends by bending from the side of the line segment connecting the two ends of the temperature sensing element and holds the temperature sensing element.

4. The surface temperature sensor according to claim 1, characterized in that the regulating members are provided in pairs on both outer sides of the pair of extension portions.

5. The surface temperature sensor according to claim 4, characterized in that the extension extends by bending from the side of the line segment connecting the pair of regulating members and holds the temperature sensing element.

6. The surface temperature sensor according to claim 1, characterized in that an insulating film is provided to cover the temperature sensing element and interposed between the temperature sensing element and the surface of the object whose temperature is to be measured.

7. The surface temperature sensor according to claim 6, characterized in that the insulating film is in contact with the temperature sensing element without containing any adhesive components.

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