Cooling device and projection type image display device

Abstract

This cooling device comprises: a Peltier element that has a first main surface and a second main surface, generates a temperature difference between the first main surface and the second main surface to make the temperature of the first main surface lower than that of the second main surface; a heat conduction member that conducts the heat of a heating element to the first main surface of the Peltier element; a cover member that covers at least a part of the heat conduction member while maintaining a space from the heat conduction member; a first sealing material that is disposed at an end part on the heating element side of the cover member and blocks the passage of outside air to the space; and a second sealing material that is disposed at an end on the Peltier element side of the cover member and blocks the passage of outside air to the space.

Description

Cooling device and projection type image display device

[0001] The present invention relates to a cooling device that cools using a Peltier element, and a projection type image display device.

[0002] Projection type image display devices are providing high-output products on the market due to increased output of light sources, improved light resistance and heat resistance of image display elements and optical devices, and the provision of power supplies capable of handling large power, and further increases in output are desired in the future. For example, a DMD (Digital Micro Mirror Device) used as an image display element is made of an inorganic material and realizes high reliability, but it is necessary to suppress heat generation within a certain temperature range.

[0003] If a heat source is connected to the cooling surface of a Peltier element via a heat conduction member that is a high thermal conductivity material, and the capacity of the Peltier element is sufficient for cooling the heat source, the heat source can be suppressed within a certain temperature range. However, when it is necessary to make the cooling surface of the Peltier element lower than the ambient temperature, condensation occurs when it drops below the ambient dew point temperature. There is a concern that if condensation occurs, it may have an adverse effect on surrounding electrical components and the like. Therefore, in view of this problem, the following proposal as in Patent Document 1 has been made conventionally.

[0004] For example, in Patent Document 1, an LED light source is temperature-controlled by a Peltier element, and a configuration is adopted in which everything from the cooling surface of the Peltier element to the LED light source is sealed to prevent condensation.

[0005] Japanese Patent Application Laid-Open No. 2007-258520

[0006] However, Patent Document 1 is effective for a case where the entire heat source can be housed in a case with a sealed structure, but it cannot be applied when the entire cooling target cannot be sealed.

[0007] An object of the present disclosure is to provide a cooling device and a projection type image display device that suppress the occurrence of condensation.

[0008] The cooling device according to this disclosure comprises a Peltier element having a first main surface and a second main surface, which generates a temperature difference between the first main surface and the second main surface by applying an electric current from the outside, thereby lowering the temperature of the first main surface compared to the second main surface; a heat conduction member that conducts the heat of a heating element to the first main surface of the Peltier element; a cover member that covers at least a part of the heat conduction member while maintaining a gap between itself and the heat conduction member; a first sealing material disposed at the end of the cover member on the heating element side and blocking the ventilation of outside air into the gap; and a second sealing material disposed at the end of the cover member on the Peltier element side and blocking the ventilation of outside air into the gap.

[0009] The projection-type image display device according to this disclosure comprises the cooling device described above, a light source, an illumination optical system that guides light from the light source to an image display element, a digital micromirror device as an image display element that modulates incident light based on an external signal, and a projection optical lens that magnifies and projects the image on the digital micromirror device.

[0010] This disclosure can provide a cooling device that suppresses the occurrence of condensation, and a projection-type image display device.

[0011] Cross-sectional view of the cooling device in Embodiment 1. Exploded perspective view of the cooling device in Embodiment 1. Enlarged view showing the structure around the O-ring in Embodiment 1. External view of the cover member in Embodiment 1. Cross-sectional view of the cooling device in Embodiment 2. Exploded perspective view of the cooling device in Embodiment 2. Enlarged view illustrating the structure around the O-ring in Embodiment 2. External view of the cover member in Embodiment 2. Cross-sectional view of the cooling device in a modified example of Embodiment 2. Overall view showing the configuration of the projection-type image display device in Embodiment 3.

[0012] The embodiments will be described in detail below, with reference to the drawings as appropriate. However, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

[0013] The attached drawings and the following description are provided to enable a person skilled in the art to fully understand this disclosure, and are not intended to limit the subject matter described in the claims.

[0014] (Embodiment 1) [1-1. Configuration of the Cooling Device] Hereinafter, an embodiment of a cooling device using a Peltier element will be described with reference to Figures 1 to 4. Figure 1 is a cross-sectional view of the cooling device 100 according to Embodiment 1, and Figure 2 is an exploded perspective view for explaining the structure of the cooling device 100. Figure 3 is an enlarged view explaining the structure around the O-ring 116, and Figure 4 is an external view of the cover member 120 seen from the inside. In each figure, the virtual heat source 101 side is considered the front, and the heat dissipation surface 107 side of the Peltier element 105 is considered the rear.

[0015] The virtual heat source 101 is a component whose temperature rises when energy is supplied from an external source, for example, but which needs to be kept at a specific temperature to ensure reliability. The heat conductive member 102 is in contact with the virtual heat source 101. The heat conductive member 102 is made of a material with excellent thermal conductivity, such as copper, aluminum, or an alloy thereof.

[0016] In the heat conductive member 102, a second contact surface 104 is provided on the side facing the first contact surface 103, which is the contact surface with the virtual heat source 101, and the second contact surface 104 comes into contact with the Peltier element 105, which is an electric heating element.

[0017] The Peltier element 105 is an element that receives power from an external source and absorbs heat from one main surface and dissipates heat from the other main surface, and is widely used in cooling applications. As shown in the figures, the Peltier element 105 has a heat-absorbing surface 106 as a first main surface and a heat-dissipating surface 107 as a second main surface. The heat-absorbing surface 106 functions as a cooling surface. A heat sink 108 is placed in contact with the heat-dissipating surface 107 of the Peltier element 105. This heat sink 108 is also made of a material with excellent thermal conductivity, such as copper, aluminum, or an alloy thereof.

[0018] Although not shown in the figures, the heat conductive member 102 is fixed to the heat sink 108, for example by screwing it in between the Peltier element 105, in order to apply an appropriate load to the Peltier element 105. At this time, the heat conductive member 102 is positioned on the cooling surface (heat absorption surface 106) side of the Peltier element 105, and the heat sink 108 is positioned on the heat dissipation surface 107 side of the Peltier element 105. As a result, the threaded portion of the connecting screw located on the heat sink 108 side becomes hot, while the head of the connecting screw located on the heat conductive member 102 side becomes cold.

[0019] If heat conduction were to occur between the heat sink 108 and the heat conductive member 102 without going through the Peltier element 105, it would lead to a decrease in the efficiency of the Peltier element 105. Therefore, the aforementioned connecting screws are assembled with an insulating material sandwiched between the head and the heat conductive member 102. In this way, the heat conductive member 102 and the heat sink 108 do not directly interfere with each other, nor are they directly connected via the heat conductive member 102. Further details will be explained in Embodiment 2, so they will be omitted here.

[0020] Numerous heat dissipation fins 109 are provided on the side of the heat sink 108 opposite to the Peltier element 105. A liquid cooling case 110 is positioned on the heat sink 108 on the side with the heat dissipation fins 109. The outer edge of the liquid cooling case 110 is in close contact with the heat sink 108, and cooling water 111 flows in from an inlet 112 through piping (not shown) to the heat dissipation fins 109 and surrounding areas of the heat sink 108, passes around the heat dissipation fins 109 of the liquid cooling case 110, and flows out from an outlet 113. At this time, the cooling water absorbs heat from the heat dissipation surface 107 of the Peltier element 105 through the heat dissipation fins 109 and is sent to an external heat sink (not shown) to be cooled, and is then circulated back to the inlet 112 by a pump (not shown).

[0021] Furthermore, as shown in Figures 2 and 3, an O-ring 116 is fitted along the corner portion formed by the annular planar portion 114 and the outer cylindrical side portion 115 of the heat conduction member 102 on the outer periphery of the heat sink 108. The O-ring 116 is an example of a second sealing member. The cover member 120 presses the O-ring 116 with a planar surface 120a near the inside of the annularly continuous outer wall 120b. The outer wall 120b extends in the front-rear direction, and the planar surface 120a faces the annular planar portion 114 of the heat sink 108 and extends inward from the front end of the outer wall 120b in a direction intersecting the front-rear direction. The annular planar portion 114 of the heat sink 108 is formed on the front surface of the outer periphery of the heat sink 108 and extends in a direction intersecting the front-rear direction.

[0022] The arms 117a to 117f of the cover member 120 are screwed to the arms 118a to 118f of the heat sink 108 to position them. At this time, the annular planar portion 114 of the heat sink 108 and the outer cylindrical side portion 115 of the heat conduction member 102 are located close to each other, but are configured so as not to directly interfere with each other. In this way, the O-ring 116 deforms between the annular planar portion 114 of the heat sink 108, the outer cylindrical side portion 115 of the heat conduction member 102, and the plane 120a near the inside of the outer wall 120b of the cover member 120, thereby blocking the air inside the heat sink 108 from the outside air.

[0023] The cover member 120 is provided with an opening peripheral end 119 on the heat source side at a position h0 from the first contact surface 103 of the heat conduction member 102. The cover member 120 does not directly interfere with the heat conduction member 102 except for the first claw portion 121 and the second claw portion 122 for positioning, and an air layer is maintained between them. As described above, the cover member 120 is in direct contact with the heat sink 108 at the arm portions 117a to 117f, so a resin material may be used for its material, considering its low thermal conductivity and ease of processing. In addition, a filler material 123 is provided between the opening peripheral end 119 of the cover member 120 and the heat conduction member 102, so the air layer inside the cover member 120 from the O-ring 116 to the filler material 123 becomes a sealed space.

[0024] As shown in Figure 1, a temperature sensor 124 is placed on the heat conduction member 102 to detect the temperature of the heat conduction member 102, between the heat conduction member 102 and the cover member 120.

[0025] The wiring leads of the temperature sensor 124 and the electrode wires 234 of the Peltier element 105 also require sealing, but this will be explained in detail in Embodiment 2 below, so the explanation is omitted here.

[0026] [1-2. Operation and Effects of the Cooling Device] In order to maintain the virtual heat source 101 at an arbitrary temperature, power is supplied to the Peltier element 105, causing the heat absorption surface 106 to be at a relatively low temperature and the heat dissipation surface 107 to be at a relatively high temperature. The Peltier element 105 dissipates energy from the heat dissipation surface 107, which is the sum of the heat absorbed and the amount of heat generated by its own heat generation. This energy is then conducted to the heat sink 108, with the heat dissipation surface 107 and a thermal conductive grease layer (not shown) in between. The heat dissipation fins 109 of the heat sink 108 are arranged with a fine pitch, and are configured to efficiently dissipate heat to the cooling water, which is the refrigerant in contact with the heat sink over a large surface area.

[0027] On the other hand, the Peltier element 105 absorbs heat from the second contact surface 104 of the heat conductive member 102, with a thermal conductive grease layer (not shown) in between. Also, the first contact surface 103 of the heat conductive member 102 is in contact with the virtual heat source 101, with a thermal conductive grease layer (not shown) in between. As a result, when controlling the virtual heat source 101 to a target temperature, the heat conductive member 102 also has thermal resistance, so a temperature gradient is created between the first contact surface 103 and the second contact surface 104. Assume that the target temperature of the virtual heat source 101 is higher than the ambient temperature, and the temperature of the second contact surface 104 is lower than the ambient temperature.

[0028] In particular, when the temperature of the second contact surface 104 is lower than the dew point, if the heat conductive member 102 comes into direct contact with the air, condensation will occur from the second contact surface 104 down to a point below the dew point. Since moisture is supplied from the surrounding air even after condensation, the dew will flow out, and if there are electrical components nearby, there is a risk of a short circuit.

[0029] In this invention, there is an air layer between the heat conductive member 102 and the cover member 120, but it is sealed by the filler material 123 and O-ring 116 applied to the opening peripheral end 119 on the heat source side. Furthermore, an air layer is also created in the area between the heat conductive member 102 and the heat sink 108 where there is no Peltier element 105, but the air in this space is also isolated from the outside air. The lead wires of the Peltier element 105 pass through holes drilled in the heat sink 108, but the space between the lead wires and the holes in the heat sink 108 is also sealed with filler material.

[0030] Thus, although there is moisture in the sealed air, it is isolated from the outside, so even if condensation occurs, it will be very small, and it is unlikely that enough dew will form to leak out. Furthermore, even if dew does form, it will not flow out into the surroundings because it is sealed.

[0031] Furthermore, since the temperature sensor 124 is in close contact with the heat conduction member 102, the temperature of the heat conduction member 102 can be detected. As described above, a temperature gradient is generated between the first contact surface 103 and the second contact surface 104 in the heat conduction member 102. When the temperature difference TD1 from the first contact surface 103 to the temperature sensor 124 and the temperature difference TD2 from the first contact surface 103 to the heat source side opening peripheral end 119 of the cover member 120 are taken, a temperature difference of (TD1 - TD2) is generated. If the temperature of the temperature sensor 124 is T1 and the ambient temperature is T0, then if the Peltier is controlled so that the following relationship is obtained, condensation will not occur in the exposed portion as described above. T1 + (TD1 - TD2) ≥ T0 ... (1)

[0032] The relationship in equation (1) holds true even when the ambient humidity is 100%. Note that the temperature gradient is greatly affected by the shape and can be estimated using heat transfer simulation. In reality, 100% humidity in the ambient air is rare, and the amount of saturated water vapor is determined by the ambient air and humidity, so there is a margin of safety equal to the temperature difference up to the dew point temperature.

[0033] In this way, when a heat source is cooled using a Peltier element 105, even if the heat-absorbing surface (cooling surface) 106 of the Peltier element 105 becomes lower than the ambient temperature, it will not cause condensation in the surrounding area. Furthermore, even if a sealed structure cannot be created due to the configuration around the heat source and it is partially exposed, condensation can be prevented.

[0034] In this example, the sealed space between the heat conduction member 102, the cover member 120, and the heat sink 108 is simply filled with air. However, by using a sealed structure, it is also possible to eliminate condensation inside the sealed space by filling it with dry air (without humidity) or nitrogen.

[0035] The cooling device 100 of Embodiment 1 includes a Peltier element 105 having a heat-absorbing surface 106 and a heat-dissipating surface 107, which generates a temperature difference between the heat-absorbing surface 106 and the heat-dissipating surface 107 by applying an electric current from the outside, thereby lowering the temperature of the heat-absorbing surface 106 compared to the heat-dissipating surface 107; a heat-conducting member 102 that conducts heat from a virtual heat source 101 to the heat-absorbing surface 106 of the Peltier element 105; a cover member 120 that maintains a gap between itself and the heat-conducting member 102 and covers at least a part of the heat-conducting member 102; a filler material 123 disposed at the end of the cover member 120 on the virtual heat source 101 side and blocking the passage of outside air into the gap; and an O-ring disposed at the end of the cover member 120 on the Peltier element 105 side and blocking the passage of outside air into the gap.

[0036] By maintaining a gap between the heat conductive member 102 and the cover member 120, for example, an air layer can be formed, improving heat insulation and suppressing condensation. Furthermore, since there is no need to seal the virtual heat source 101, condensation can be suppressed with a compact configuration.

[0037] (Embodiment 2) Hereinafter, Embodiment 2 of a cooling device using a Peltier element will be described with reference to Figures 5 to 9. Figure 5 is a cross-sectional view of the cooling device 200 according to Embodiment 2, and Figure 6 is an exploded perspective view for explaining the structure of the cooling device 200. Figure 7 is an enlarged view explaining the structure around the O-ring 223, Figure 8 is an external view showing the inside of the cover member 224, and Figure 9 is a cross-sectional view of the applied and expanded cooling device.

[0038] [2-1. Configuration of the Cooling Device in Embodiment 2] The cooling device 200 in Embodiment 2 cools and regulates the temperature of the DMD 201, which serves as a heat source. The DMD 201 is an image display element in which a miniature mirror, whose tilt angle can be independently selected, is arranged in an array, and it generates image light by controlling the reflection direction of incident light. Although the DMD 201 has excellent light resistance, it needs to be controlled within a certain temperature range. The DMD 201's temperature rises due to the absorption of some of the incident light or due to self-heating during operation.

[0039] Therefore, heat needs to be dissipated from the back surface 202 of the DMD201. The DMD201 is equipped with numerous small terminals and is housed in a holder 204 that makes electrical connections with the electrical circuit board 203 for power supply and receiving external signals. In the aforementioned electrical circuit board 203 and holder 204, an opening is provided on the back side, which roughly corresponds to the image display section of the DMD201, in order to dissipate heat from the back surface 202 of the DMD201.

[0040] A heat conductive member 205 is in contact with the back surface 202 of the DMD 201 at a first contact surface 206. The heat conductive member 205 is also made of a material with excellent thermal conductivity. A second contact surface 207 is provided on the opposite side of the first contact surface 206, and the Peltier element 208 is in contact with the second contact surface 207 with a layer of heat conductive grease (not shown) in between.

[0041] The Peltier element 208 is sandwiched between the heat conductive member 205 and the heat sink 209 and pressed at four points by a screw 210, a spring washer 211, a flat washer 212, and a bush 213. The bush 213 is made of a material with low thermal conductivity, such as resin, and the screw 210 is screwed into the heat sink 209, where the temperature is high, so it is installed to provide insulation and prevent heat transfer to the heat conductive member 205.

[0042] The first contact surface 206 of the heat conduction member 205 has a rectangular shape, and at a position away from the contact surface, its cross-section is substantially rectangular and gradually larger than the first contact surface 206. The second contact surface 207 on the side of the Peltier element 208 has a circular outer shape, but inside it, a step is formed with an increased thickness along the rectangular shape of the Peltier element 208, and the cross-sectional area increases or has the same shape from the first contact surface 206 to the second contact surface 207 side. Thereby, the heat absorbed from the first contact surface 206 of the heat conduction member 205 diffuses, suppressing an increase in thermal resistance and improving the cooling efficiency of the Peltier element 208, and the burden can be suppressed.

[0043] In the Peltier element 208, 214 is the heat absorption surface and 215 is the heat dissipation surface. A heat dissipation plate 209 is arranged in contact with the heat dissipation surface 215 of the Peltier element 208 with a heat conduction grease layer (not shown in the figure) interposed therebetween. This heat dissipation plate 209 is also made of a material such as copper, aluminum, or their alloys with excellent thermal conductivity, and heat dissipation fins 216 are provided on the surface opposite to the contact surface of the Peltier element 208.

[0044] The heat dissipation fins 216 are formed, for example, by raising a part of the heat dissipation plate 209 and have a fine shape such as a thickness of 0.3 mm and a pitch of 0.6 mm. A liquid cooling case 217 is arranged so as to cover the heat dissipation fins 216. The outer edge portion of the liquid cooling case 217 is in close contact with the heat dissipation plate 209, and a heat exchange chamber to accommodate the heat dissipation fins 216, 218, is provided at the center thereof.

[0045] The cooling water, which is the refrigerant, flows in from the inlet 219 through a pipe (not shown in the figure), takes heat from the heat dissipation fins 216 when passing through the heat exchange chamber 218 and then the temperature rises, and then flows out from the outlet 220. After that, the cooling water is circulated in the same manner as in the first embodiment.

[0046] Here too, as described in the first embodiment and FIG. 3, an O-ring, 223, is mounted along the corner formed by the annular flat portion 221 on the outer periphery of the heat dissipation plate 209 and the outer peripheral cylindrical side surface portion 222 of the heat conduction member 205. The cover member 224 presses the O-ring 223 at the flat surface 224a near the inside of the annular continuous outer wall 224b.

[0047] The arms 225a - f of the cover member 224 are screwed to the arms 226a - f of the heat dissipation plate 209 to determine the position. At this time, the annular flat portion 221 of the heat dissipation plate 209 and the outer peripheral cylindrical side surface portion 222 of the heat conduction member 205 are positioned close to each other, but are configured not to directly interfere. Thus, the O - ring 223 is deformed between the annular flat portion 221 of the heat dissipation plate 209, the outer peripheral cylindrical side surface portion 222 of the heat conduction member 205, and the plane 224a near the inner side of the outer wall 224b of the cover member 224 to block the air inside the heat dissipation plate 209 from the outside air.

[0048] An opening end 227 on the DMD201 side is provided at a position with an arbitrary interval h2 from the first contact surface 206 of the heat conduction member 205. The cover member 224 does not directly interfere with the heat conduction member 205 except for the first claw portion 228 and the second claw portion 229 for positioning, and an air layer is secured therebetween. As described above, since the cover member 224 directly abuts on the heat dissipation plate 209 at the arms 226a - f, its material may have a low thermal conductivity, and considering the processability, a resin material may be adopted. Also, a filler 230 is filled between the opening end 227 on the DMD201 side of the cover member 224 and the heat conduction member 205.

[0049] A temperature sensor 231 is mounted on the heat conduction member 205 to grasp the temperature of the heat conduction member 205. Although the lead wire 232 of the temperature sensor 231 penetrates the cover member 224, a filler (not shown) is also filled between the lead wire 232 and the through - hole on the cover member 224.

[0050] Furthermore, the electrode wire 234 of the Peltier element 208 penetrates a hole provided in the lower part of the annular flat portion 221 of the heat dissipation plate 209, and a sealing material (not shown) is filled between the hole of the heat dissipation plate 209 and the electrode wire 234 so that there is no air flow.

[0051] These fillers are preferably made of a material having heat resistance, no air permeability, and no gas generation. Also, a packing molded according to the shape of the sealing portion can be replaced as long as it has the same characteristics and can be closely fixed.

[0052] With the above configuration, the space between the heat conductive member 205 and the cover member 224, from the portion where the Peltier element 208 is housed to the open end 227 of the cover member 224 on the DMD 201 side, is sealed.

[0053] [2-2. Operation and Effects of the Cooling Device of Embodiment 2] In Figure 5, for the heat conductive member 205 to absorb heat from the back surface 202 of the DMD 201 more effectively than the first contact surface 206, a larger surface area is desirable. If there are limitations on the contact position within the back surface 202 of the DMD 201, as shown in the figure, the tip portion of the heat conductive member 205, which is farther from the first contact surface 206, is provided with a large cross-sectional area in a plane direction parallel to the first contact surface 206 as much as possible. Furthermore, an inclined portion 205a is provided here that extends outward toward the rear from the first contact surface 206, and is enlarged to a size that ensures a minimum gap with the opening of the holder 204. The inclination angle of the inclined portion 205a is, for example, 45 degrees, and its cross-sectional shape is not limited to a straight line but may be a curve. By providing the inclined portion 205a, the heat conduction member 205 can increase the cross-sectional area that intersects the front-rear direction toward the rear of the first contact surface 206 located within the opening of the holder 204, thereby improving heat conductivity and enhancing the cooling efficiency of the DMD 201. Furthermore, since the tip portion of the heat conduction member 205, including the first contact surface 206 and the inclined portion 205a, is not covered by the cover member 224, it can contact the back surface 202 of the DMD 201 over a larger area within the opening of the holder 204, thereby improving cooling efficiency.

[0054] On the other hand, if the surface temperature of the heat conductive member 205 is lower than the ambient temperature, there is a concern about condensation, so the cover member should be extended to the vicinity of the first contact surface 206 to seal it. However, as described above, this interferes with the opening of the holder 204 near the first contact surface 206, so the following relationship is ensured.

[0055] When h2 is the distance from the back surface 202 of the DMD201 to the tip of the opening end 227 of the cover member on the DMD201 side, and h1 is the thickness around the opening of the back surface 202 of the DMD201 in the holder 204, the following relationship holds: h2 > h1 ... (2)

[0056] According to this, by widening the cross-section of the heat conduction member 205, the thermal resistance of the heat conduction member 205 can be reduced, and when the same amount of heat is drawn from the back surface 202 of the DMD 201, the temperature of the heat absorption surface 214 of the Peltier element 208 can be increased, that is, concerns about condensation and the power input to the Peltier element 208 can be suppressed. Even with this configuration, if the amount of heat to be absorbed from the back surface 202 of the DMD 201 is large, even if the heat absorption surface 214 of the Peltier element 208 becomes lower than the ambient dew point temperature, there is no concern about condensation because, except for the tip of the heat conduction member 205, the outside air is blocked by the sealing structure as described above.

[0057] Furthermore, the same thing can be said here as in Embodiment 1. That is, because the temperature sensor 231 is in close contact with the heat conductive member 205, the temperature of the heat conductive member 205 can be detected. A temperature gradient is generated between the first contact surface 206 and the second contact surface 207 of the heat conductive member 205. When the temperature difference TD1 from the first contact surface 206 to the temperature sensor 231 is taken as TD2, and the temperature difference of the portion exposed to the outside of the cover member 120 from the first contact surface 206 to the opening end 227 on the DMD 201 side of the cover member 224 is taken as TD2, a temperature difference of (TD1 - TD2) is generated. Therefore, if the temperature of the temperature sensor 231 is T1 and the ambient temperature is T0, then if the Peltier is controlled so that the following relationship is obtained, condensation will not occur in the exposed portion as described above. T1 + (TD1 - TD2) ≥ T0 ... (3)

[0058] These are the same as in Embodiment 1, but the amount of heat generated by the heat source DMD201 varies depending on the state of the mirror drive (the tilt and number of the micro-mirrors), especially when the amount of incident light changes. Therefore, in the case where the amount of incident light to the DMD201 changes, and the state of the mirror drive changes over time due to the display of video or the like, it is necessary to obtain information on the amount of incident light and to obtain TD1 and TD2 in advance according to the drive state of the micro-mirrors so that the relationship in equation (3) is satisfied in the state at that time.

[0059] Furthermore, as shown in Figure 9, the electrical circuit board 203 is pressed against the holder 204 on the side of the DMD 201 opposite to the back surface 202, and the electrical circuit board 203 and the DMD 201 are electrically connected by a number of contact pins incorporated into the holder 204. As a result, signals input to the electrical circuit board 203 from the outside reach the DMD 201 via the holder 204, and the desired drive is achieved.

[0060] Similar to the holder 204, the electrical circuit board 203 is also provided with a hole 203a through which the heat conductive member 205 passes. Here, there is no problem if the size of the hole 203a in the electrical circuit board 203 is larger than the opening end 227 of the cover member 224. However, if the size of the hole 203a in the electrical circuit board 203 is smaller than or about the same as the opening end 227 of the cover member 224, then, when h2 is the distance from the back surface 202 of the DMD 201 to the tip of the heat conductive member 205, and h3 is the thickness from the back surface 202 of the DMD 201 to the cover member 224 side of the electrical circuit board 203, the following relationship holds: h2 > h3 ... (4)

[0061] According to the relationship in equation (4), even if the opening through which the heat conductive member 205 of the electrical substrate 203 that drives the DMD 201 passes is not sufficiently large, the concern of condensation on the heat conductive member 205 can be minimized.

[0062] In embodiments 1 and 2, the heat dissipation of the heat sink on the heat dissipation side of the Peltier element was performed by liquid cooling. However, if the amount of heat to be processed is not large, this can be replaced with cooling means such as a heat sink or heat pipe.

[0063] (Embodiment 3) Figure 10 is an overall diagram showing the configuration of the projection-type image display device according to Embodiment 3.

[0064] [3-1. Configuration of the projection-type image display device of Embodiment 3] In the projection-type image display device 300, as shown in Figure 10, the light source unit consists of a laser light source unit 301 that emits blue light, a laser light source unit 302 that emits green light, and a laser light source unit 303 that emits red light. The colored light from these light sources is superimposed by a blue reflection color selection mirror 304 and a red reflection color selection mirror 305, and then focused onto a rod integrator 309 by lenses 306, mirror 307, and lens 308.

[0065] Light emitted from the rod integrator 309 passes through relay lenses 310 and 311, is reflected by the folding mirror 312, then passes through the field lens 313, and enters the total internal reflection prism 314. In the total internal reflection prism 314, the first prism 315 and the second prism 316 are fixed while maintaining a small gap (air gap). Light incident on the total internal reflection prism 314 is totally reflected by the total internal reflection surface 317, and then passes through surface 318 before entering the color prism unit 319.

[0066] This color prism unit 319 is bonded together with a first prism 321 having a blue-transmitting dichroic mirror surface 320 that reflects blue light, and a second prism 326 and a third prism 327 having a green-transmitting dichroic mirror surface 322 that reflects red and blue light. However, an air gap is provided between the first prism 321 and the second prism 326 to utilize total internal reflection.

[0067] Each prism end face is equipped with DMD328R, 328G, and 328B as shown in the figure. These DMDs consist of tiny mirrors arranged in two dimensions, and their tilt direction is controlled in two directions according to the external video signal. When the signal is ON, the reflected light returns to the color prism unit 319 at an incident angle of 0°, and when the signal is OFF, it re-enters the color prism unit 319 at a larger angle. DMD328B is for blue light modulation, DMD328R is for red light modulation, and DMD328G is for green light modulation.

[0068] In the DMDs 328R, 328G, and 328B, the white display mode signals for each pixel return to the color prism unit 319. After passing through this unit, the signals pass through the first prism 315 and the second prism 316 of the total internal reflection prism 314, enter the projection lens 329, and reach a screen (not shown). Therefore, color display can be achieved by inputting different signals to the DMDs 328R, 328G, and 328B. The cooling devices described in Embodiment 2 are attached to the back of each of these DMDs.

[0069] In the projection-type image display device 300, which houses the laser illumination and projection unit 330 configured as described above, the housing 331 is equipped with an intake fan 333 that takes in outside air from an intake port 332 and a radiator 334 that cools the liquid coolant flowing inside by ventilation. An intake fan 336 for the electrical circuit is provided at one end of the electrical circuit unit 335, which takes in outside air from an intake port 337 for the electrical circuit and cools the electrical circuit unit 335. The air that is drawn in and whose temperature has risen is discharged to the outside from an exhaust port 339 by an exhaust fan 338. Here, a temperature sensor 340 is provided near the intake port 332 at a position that comes into contact with the outside air taken in.

[0070] Each DMD is equipped with a cooling device according to Embodiment 2 on its rear surface. Cooling device 200R is installed on the red DMD328R, cooling device 200G on the green DMD328G, and cooling device 200B on the blue DMD328B. The configuration is the same as in Embodiment 2, so the explanation will be omitted, but the ambient temperature T0 in the above explanation can be obtained from the output of the temperature sensor 340.

[0071] [3-2. Operation and Effects of the Projection-Type Image Display Device of Embodiment 3] The DMDs 328R, 328G, and 328B for each color are driven via an electrical circuit unit 335 and an electrical circuit board 203 using signal cables (not shown). An external video signal is input to the electrical circuit unit 335, and the DMDs are controlled accordingly according to the color of light. The ratio of red, green, and blue light energy incident on each DMD changes depending on the target white balance, and the ratio at which the same amount of light (e.g., the same lumen) is converted into heat differs for each color of light. Furthermore, the amount of light absorbed also changes depending on the tilt of the minute mirrors of the DMD, so the amount of heat absorbed changes depending on the video signal level (ON / OFF ratio).

[0072] Therefore, data relating the video signal level and DMD heat generation is pre-stored within the device for each color DMD, and the back temperature of each color DMD can be predicted from this data and the value from the temperature sensor 340. This allows for the control of the Peltier elements in the cooling devices 200R for the red DMD, 200G for the green DMD, and 200B for the blue DMD.

[0073] In this case, if the temperature of the portion of the heat conductive member 205 near the back surface 202 of the DMD 201 that is exposed from the cover member 224, as estimated from the temperature of the temperature sensor 231 in each cooling device, is higher than that of the temperature sensor 340, or if the temperature at the location of the temperature sensor 231 is lower than that of the temperature sensor 340 but the temperature of the exposed portion of the heat conductive member 205 is predicted to be the same as or higher than that of the temperature sensor 340, then it is not necessary to change the drive of the Peltier element each time according to the video signal level.

[0074] In this way, when cooling the back surface temperature of the DMD201 with a Peltier element, condensation does not occur, ensuring the reliability of the DMD while simultaneously preventing problems such as electrical short circuits and corrosion caused by condensation during cooling.

[0075] As described above, embodiments have been explained as examples of the technology in this disclosure. For this purpose, attached drawings and a detailed description have been provided. Therefore, among the components described in the attached drawings and detailed description, there may be not only components that are essential for solving the problem, but also components that are not essential for solving the problem, in order to illustrate the technology described above. Therefore, the mere presence of such non-essential components in the attached drawings and detailed description should not be immediately assumed to mean that those non-essential components are essential.

[0076] Furthermore, since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0077] (Outline of Embodiments) (1) The cooling device of the present disclosure comprises a Peltier element having a first main surface and a second main surface, which generates a temperature difference between the first main surface and the second main surface by applying an electric current from the outside, thereby lowering the temperature of the first main surface compared to the second main surface; a heat conduction member that conducts the heat of a heating element to the first main surface of the Peltier element; a cover member that covers at least a part of the heat conduction member while maintaining a gap between itself and the heat conduction member; a first sealing material disposed at the end of the cover member on the heating element side and blocking the ventilation of outside air into the gap; and a second sealing material disposed at the end of the cover member on the Peltier element side and blocking the ventilation of outside air into the gap.

[0078] This allows for the formation of an air layer, for example, by maintaining a gap between the heat-conducting member and the cover member, thereby improving thermal insulation and suppressing condensation. Furthermore, since there is no need to seal the heat-generating element, condensation can be suppressed in a compact configuration.

[0079] (2) In the cooling device of (1), the heat conduction member has an exposed portion at the end on the heat-generating element side that is exposed from the cover member.

[0080] (3) In the cooling device of (2), the heat conductive member is in contact with the outside air at the exposed portion.

[0081] (4) In any one of the cooling devices described in (1) to (3), the heat conduction member and the cover member are in contact with each other via a projection that maintains a distance between them.

[0082] (5) In any one of the cooling devices described in (1) to (4), the second sealing material includes an elastic material, and the Peltier element and the cover member are in contact via the second sealing material.

[0083] (6) In the cooling device of (5), the second sealing material has a closed shape with an opening in the center. The inner diameter side of the second sealing material is in contact with the outer peripheral surface of the heat conduction member, the rear side of the second sealing material is in contact with the front surface of the heat sink plate, and the outer diameter side of the second sealing material is in contact with the flat surface on the inner side of the outer wall of the cover member.

[0084] (7) In the cooling device of (6), the second sealing material is a packing.

[0085] (8) In any one of the cooling devices described in (1) to (7), the heat-generating element is a digital micromirror device.

[0086] (9) The cooling device of (8) is provided with a holder on which a digital micromirror device is mounted. The holder has an opening in the center such that the heat dissipation surface of the digital micromirror device is exposed. When the thickness of the opening of the holder is h1 and the distance from the contact surface of the heat conductive member with the digital micromirror device to the heat-generating end face of the cover member is h2, the following relationship holds: h1 < h2.

[0087] In the cooling device of (10)(9), the digital micromirror device has electrical contacts on its back surface. The cooling device includes an electrical substrate that is electrically connected to the electrical contacts and has an opening. The electrical substrate is positioned so as to contact the surface of the holder opposite to the surface in contact with the digital micromirror device, such that the heat dissipation surface on the back of the digital micromirror device is exposed through the opening in the electrical substrate. When the distance from the back surface of the digital micromirror device to the surface of the electrical substrate opposite to the digital micromirror device is h3, the following relationship holds: h3 < h2.

[0088] In any one of the cooling devices of (11)(8) to (10), the heat conduction member comprises a first contact surface that contacts a digital micromirror device and a second contact surface that contacts a Peltier element. The first contact surface has a rectangular shape, and the cross-section of the heat conduction member at a position away from the first contact surface toward the second contact surface is substantially rectangular and larger than that of the first contact surface. The second contact surface has a circular outer shape, and the thickness of the heat conduction member is increased in a rectangular shape on the inside of the second contact surface, along the rectangular shape of the Peltier element, in the direction opposite to the contact direction with the Peltier element. The cross-sectional area of ​​the heat conduction member increases from the first contact surface to the second contact surface.

[0089] (12) In any one of the cooling devices described in (1) to (11), the first sealing material is an adhesive or a filler.

[0090] (13) In any one of the cooling devices described in (1) to (12), a temperature sensor is provided mounted on a heat conduction member within a range sealed by a cover member.

[0091] (14) In the cooling device of (13), the portion of the heat conduction member exposed from the cover member is at a temperature higher than the ambient temperature.

[0092] (15) The projection image display device of the present disclosure comprises any one of the cooling devices (1) to (14), a light source, an illumination optical system that guides light from the light source to an image display element, a digital micromirror device as an image display element that modulates incident light into image light based on an external signal, and a projection optical lens that magnifies and projects the image light.

[0093] (16) The projection-type image display device of (15) comprises a housing that houses a cooling device, a light source, an illumination optical system, a digital micromirror device, and a projection optical lens, and a temperature measuring unit capable of measuring a temperature outside the housing or a temperature that can be considered outside the housing. The Peltier element is controlled so that the exposed portion of the heat conductive member exposed from the cover member reaches a temperature that is outside the housing or a temperature that can be considered outside the housing.

[0094] This disclosure is applicable to cooling devices equipped with Peltier elements and image display devices equipped with them.

[0095] 100, 200, 200R, 200G, 200B Cooling device 101 Virtual heat source 102, 205 Heat conductive member 103, 206 First contact surface 104, 207 Second contact surface 105, 208 Peltier element 106, 214 Heat absorption surface 107, 215 Heat dissipation surface 108, 209 Heat sink plate 109, 216 Heat dissipation fin 110, 217 Liquid cooling case 111 Cooling water 112, 219 Inlet 113, 220 Outlet 114, 221 Outer circular annular planar section 115, 222 Outer cylindrical side section 116, 223 O-ring 117a-f, 225a-f Arm section of cover member 118a-f, 226a-f Heat sink arm portion 119 Opening peripheral end portion 120, 224 Cover member 120a, 224a Plane 120b, 224b Outer wall 121, 228 First claw portion 122, 229 Second claw portion 123, 230, 233, 235 Filler material 124, 231 Temperature sensor 201 DMD 202 Back 203 Electrical circuit board 204 Holder 210 Screw 211 Spring washer 212 Flat washer 213 Bushing 218 Heat exchange chamber 227 Open end 232 Lead wire of temperature sensor 234 Electrode wire of Peltier element 300 Projection type image display device 301 Blue light laser light source unit 302 Green light laser light source unit 303 Red light laser light source unit 304 Blue reflective color-selecting mirror 305 Red reflective color-selecting mirrors 306, 308 Lenses 307, 312 Mirror 309 Rod integrator 310, 311 Relay lens 313 Field lens 314 Total reflection prism 315 First prism 316 Second prism 317 Total reflection surface 318 Transmitting surface of the second prism 319 Color prism unit 320 Blue transmitting dichroic mirror surface 321 First prism 322 Green transmitting dichroic mirror surface 326 Second prism 327 Third prism 328R, 328G, 328B DMD 329 Projection lens 330 Laser illumination and projection unit 331 Housing 332 Air intake 333 Air intake fan 334 Radiator 335 Electrical circuit unit 336 Intake fan 337, Intake port 338, Exhaust fan 339, Exhaust port 340, Temperature sensor

Claims

1. A cooling device comprising: a Peltier element having a first main surface and a second main surface, which generates a temperature difference between the first main surface and the second main surface by applying an electric current from the outside, thereby lowering the temperature of the first main surface compared to the second main surface; a heat conduction member that conducts heat from a heating element to the first main surface of the Peltier element; a cover member that covers at least a portion of the heat conduction member while maintaining a gap between itself and the heat conduction member; a first sealing material disposed at the end of the cover member on the heating element side and blocking the passage of outside air to the gap; and a second sealing material disposed at the end of the cover member on the Peltier element side and blocking the passage of outside air to the gap.

2. The cooling device according to claim 1, wherein the heat conductive member has an exposed portion at the end on the heating element side that is exposed from the cover member.

3. The cooling device according to claim 2, wherein the heat conductive member is in contact with the outside air at the exposed portion.

4. The cooling device according to claim 1, wherein the heat conductive member and the cover member are in contact with each other at a projection that maintains the aforementioned distance.

5. The cooling device according to claim 1, wherein the second sealing material includes an elastic material, and the Peltier element and the cover member are in contact via the second sealing material.

6. The cooling device according to claim 5, wherein the second sealing material has a closed shape with an opening in the center, the inner diameter side of the second sealing material is in contact with the outer peripheral side surface of the heat conducting member, the rear side of the second sealing material is in contact with the front surface of the heat sink, and the front side of the second sealing material is in contact with the inner flat surface of the cover member.

7. The cooling device according to claim 6, wherein the second sealing material is a packing.

8. The cooling device according to claim 1, wherein the heating element is a digital micromirror device.

9. A cooling device according to claim 8, comprising a holder on which the digital micromirror device is mounted, wherein the holder has an opening in its center such that the heat dissipation surface of the digital micromirror device is exposed, and when the thickness of the opening in the holder is h1 and the distance from the contact surface of the heat conductive member with the digital micromirror device to the end face of the cover member on the heat-generating element side is h2, the following relationship holds: h1 < h2 10. The cooling device according to claim 9, wherein the digital micromirror device has electrical contacts on its back surface, the cooling device comprises an electrical substrate electrically connected to the electrical contacts and having an opening, the electrical substrate is positioned so as to contact the surface of the holder opposite to the surface in contact with the digital micromirror device, such that the heat dissipation surface on the back surface of the digital micromirror device is exposed through the opening of the electrical substrate, and the following relationship holds when the distance from the back surface of the digital micromirror device to the surface of the electrical substrate opposite to the digital micromirror device is h3: h3 < h2 11. The cooling device according to claim 8, wherein the heat conductive member comprises a first contact surface that contacts the digital micromirror device and a second contact surface that contacts the Peltier element, the first contact surface having a rectangular shape, the cross-section of the heat conductive member at a position away from the first contact surface toward the second contact surface being substantially rectangular and larger than that of the first contact surface, the second contact surface having a circular outer shape, the thickness of the heat conductive member increasing in a rectangular shape on the inside of the second contact surface along the rectangular shape of the Peltier element in the direction opposite to the contact direction with the Peltier element, and the cross-sectional area of ​​the heat conductive member increasing from the first contact surface to the second contact surface.

12. The cooling device according to claim 1, wherein the first sealing material is an adhesive or a filler.

13. The cooling device according to claim 1, further comprising a temperature sensor mounted on the heat conductive member within the area sealed by the cover member.

14. The cooling device according to claim 13, wherein the portion of the heat conductive member exposed from the cover member is at a temperature equal to or higher than the ambient temperature.

15. A projection-type image display device comprising: a cooling device according to claim 1; a light source; a digital micromirror device that modulates incident light from the light source into image light based on an external signal; and a projection optical lens that projects the image light.

16. The projection-type image display device according to claim 15, comprising: a housing housing the cooling device, the light source, the digital micromirror device, and the projection optical lens; and a temperature measuring unit capable of measuring a temperature outside the housing or a temperature that can be considered to be outside the housing, wherein the Peltier element is controlled so that the exposed portion of the heat conductive member exposed from the cover member reaches a temperature that can be considered to be outside the housing or a temperature that can be considered to be outside the housing.

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