Patent Publication Number: US-7907045-B2

Title: Hoisting machine

Description:
TECHNICAL FIELD 
     The present invention relates to hoisting machines, such as electric chain blocks and electric hoists, which drive a load hoisting motor with an inverter incorporated therein. More particularly, the present invention relates to a hoisting machine capable of efficiently dissipating heat generated from the inverter into the surrounding air and also capable of efficiently dissipating, into the surrounding air, heat generated from a regenerative braking resistor when supplied with a regenerative electric current generated during regenerative braking of the load hoisting motor, and hence capable of performing high-frequency operation. 
     BACKGROUND ART 
     There are hoisting machines, such as electric chain blocks and electric hoists, which use as a load hoisting motor an inverter-driven motor that is driven by an inverter incorporated in the hoisting machine main body. In such a hoisting machine, when the temperature of the inverter exceeds a predetermined set temperature, the inverter is tripped (shut off) to stop the operation of the hoisting machine from the viewpoint of safety. When a hoisting machine is operated at high frequency, i.e. when the operating time of the hoisting machine accounts for 60% or more of the sum total (100%) of the operating time and down time, a large amount of heat is generated from the inverter, and the heat undesirably stays in a control box housing the inverter. When the temperature in the control box exceeds the above-described predetermined set temperature (e.g. 100° C.), the inverter is tripped to stop the operation of the hoisting machine. 
       FIG. 1  is a sectional plan view showing the internal structure of a control box of a conventional electric chain block of the type described above. A control box  100  houses an inverter  102 , an electromagnetic switch  103  and a transformer  104  that are mounted on a steel panel  101 . When the electric chain block is operated at high frequency, a large amount of heat is generated from the inverter  102  as stated above. Because the panel  101  is made of steel, it is inferior in thermal conductivity to aluminum or other similar material. The panel  101  is also inferior in heat dissipation properties because it is thin in thickness. Therefore, the heat generated from the inverter  102  cannot escape but undesirably stays in the control box  100 , causing the temperature to rise. As a result, the inverter  102  is tripped. It should be noted that reference numeral  105  in  FIG. 1  denotes a speed reduction mechanism casing that houses a speed reduction mechanism (detailed later) of the electric chain block. 
     As a countermeasure against this problem, there is a method wherein, as shown in  FIG. 2 , the control box  100  is made of aluminum, and the inverter  102  is attached to the inner wall surface of the control box  100 . With this method, the control box  100  is made of an aluminum material of good thermal conductivity, and the outer wall surface of the control box  100  is exposed to the surrounding air. Therefore, it is possible to expect that heat generated from the inverter  102  can be effectively dissipated. With this structure, however, wiring and maintenance are troublesome because the components other than the inverter  102 , i.e. the electromagnetic switch  103  and the transformer  104 , are attached to the main body side of the hoisting machine through the panel  101 . Further, there is a fear that a possible impact on the control box  100  will be applied directly to the inverter  102 . 
     Further, when the above-described hoisting machine lowers a lifted load, the load hoisting motor functions as a generator, and a regenerative electric current thus generated is passed through a regenerative braking resistor to consume it as heat, thereby regeneratively braking the load hoisting motor. 
       FIG. 3  is a diagram showing a structural example of a conventional regenerative braking resistor of the type described above.  FIG. 3(   a ) is a plan view.  FIG. 3(   b ) is a front view.  FIG. 3(   c ) is a right-hand side view. As illustrated in the figures, a resistor  110  comprises a rectangular parallelepiped metallic casing  111  formed from a metal plate (e.g. an aluminum plate), resistance elements of continuous length (e.g. resistance elements each comprising a nichrome wire wound around a rod member of a heat-resisting insulating material)  112  disposed in the metallic casing  111 , and a heat-resisting insulating material  113  of an inorganic material filled in the space in the metallic casing  111  other than the space occupied by the resistance elements  112 . The resistance elements  112  are electrically connected in series at one end of each with a lead wire  115  in the metallic casing  111 . Lead wires  114  connected to the other ends of the resistance elements  112  extend from an end of the metallic casing  111 . 
     In the case of using as a regenerative braking resistor a resistor having resistance elements  112  disposed in a rectangular parallelepiped metallic casing  111  as stated above, when the hoisting machine is operated at high frequency, a large amount of electric current flows through the regenerative braking resistor, resulting in a rise in temperature. The temperature rise causes the temperature of the inverter to rise as well. If the inverter temperature exceeds the above-described set temperature, the inverter is tripped. In a case where the load hoisting motor generates a large regenerative electric current, a plurality of resistors  110  need to be used. In such a case, it takes time and labor to wire and install the resistors  110 . 
     As a countermeasure to be taken under circumstances where the motor generates a large amount of regenerative electric current during lowering of a load, there is a method wherein, as shown in  FIG. 4(   a ), an increased number of resistance elements  112  are disposed in the metallic casing  111 . With this method, however, the resistance elements  112  radiate heat toward each other and thus release a large amount of heat. On the other hand, the surface area of the metallic casing  111  cannot be increased sufficiently. Thus, the method is inferior in heat dissipation properties. To cope with this problem, there has been proposed a method wherein, as shown in  FIG. 4(   b ), the resistor  110  is equipped with a heatsink  120  as a discrete member. This method suffers, however, from the problem that there is an increase in the dimensions of the resistor  110  including the heatsink  120 , particularly the height dimension. In addition, if the condition of contact between the heatsink  120  and the resistor  110  is not satisfactory, the heat dissipation properties degrade. Further, the use of the heatsink  120  increases the number of component parts correspondingly and causes an increase in cost.
     Patent Literature 1: Japanese Patent Application Publication No. Hei 8-91784   Patent Literature 2: Japanese Examined Utility Model Application Publication No. Hei 5-39603   Patent Literature 3: Japanese Patent Application Publication No. Hei 10-32101   

     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention has been made in view of the above-described circumstances. Accordingly, an object of the present invention is to provide a hoisting machine capable of efficiently dissipating heat generated from an inverter and a regenerative braking resistor incorporated therein into the surrounding air with a simple structure and hence capable of performing high-frequency operation. 
     Solution to Problem 
     To solve the above-described problem, the present invention provides a hoisting machine having a load hoisting motor and a speed reduction mechanism and driving the load hoisting motor with an inverter incorporated in the hoisting machine main body. The hoisting machine is characterized by being provided with a heat dissipation means that dissipates heat generated from the inverter to a speed reduction mechanism casing that houses the speed reduction mechanism. 
     Thus, the hoisting machine is provided with a heat dissipation means that dissipates heat generated from the inverter to the speed reduction mechanism casing. Therefore, heat generated from the inverter can be efficiently dissipated to the surrounding air through the speed reduction mechanism casing having a large heat capacity. Further, because the interior of the speed reduction mechanism casing is an oil bath containing a lubricating oil, it is possible to expect cooling of the inverter by oil cooling. Accordingly, the inverter can be efficiently cooled, and the hoisting machine can be operated at high frequency. 
     In addition, the hoisting machine of the present invention is characterized in that the heat dissipation means is a means for attaching the inverter to the speed reduction mechanism casing in close contact therewith through surface contact at least a part of the inverter to dissipate heat generated from the inverter to the speed reduction mechanism casing. 
     Thus, the heat dissipation means is a means for attaching the inverter directly to the speed reduction mechanism casing in close contact therewith through surface contact at least a part of the inverter to dissipate heat generated from the inverter to the speed reduction mechanism casing. Therefore, heat generated from the inverter can be efficiently transferred and dissipated to the speed reduction mechanism casing with a simple structure. Further, because the inverter is attached directly to the speed reduction mechanism casing in close contact therewith, no space or member is interposed between the inverter and the speed reduction mechanism casing, and hence the hoisting machine can be constructed in a correspondingly compact form as a whole. 
     In addition, the hoisting machine of the present invention is characterized in that the speed reduction mechanism casing is made of an aluminum material. 
     Thus, the speed reduction mechanism casing is made of an aluminum material having a high thermal conductivity. Therefore, heat generated from the inverter can be dissipated speedily and even more efficiently. 
     In addition, the hoisting machine of the present invention is characterized in that the speed reduction mechanism casing is formed by aluminum the casting. 
     Thus, the speed reduction mechanism casing is formed by aluminum the casting. Because the aluminum die casting process enables the wall thickness of the speed reduction mechanism casing to be increased as compared to pressing, heat generated from the inverter can be efficiently transferred to the speed reduction mechanism casing. 
     In addition, the present invention provides a hoisting machine having a load hoisting motor, a speed reduction mechanism and a regenerative braking resistor and driving the load hoisting motor with an inverter incorporated in the hoisting machine main body and further passing an electric current generated by the load hoisting motor during lowering of a lifted load through the regenerative braking resistor to apply regenerative braking. The hoisting machine is characterized by being provided with a heat dissipation means that dissipates heat generated from the inverter to a speed reduction mechanism casing that houses the speed reduction mechanism. 
     Thus, the hoisting machine is provided with a heat dissipation means that dissipates heat generated from the inverter to the speed reduction mechanism casing. Therefore, heat generated from the inverter can be efficiently dissipated to the surrounding air through the speed reduction mechanism casing having a large heat capacity. Further, because the interior of the speed reduction mechanism casing is an oil bath containing a lubricating oil, it is possible to expect cooling of the inverter by oil cooling. Accordingly, the inverter can be efficiently cooled, and the inverter temperature can be maintained below a predetermined trip temperature. Thus, the hoisting machine can be operated at high frequency. 
     In addition, the hoisting machine of the present invention is characterized in that the heat dissipation means is a means for attaching the inverter to the speed reduction mechanism casing in close contact therewith through surface contact at least a part of the inverter to dissipate heat generated from the inverter to the speed reduction mechanism casing. 
     Thus, the heat dissipation means is a means for attaching the inverter to the speed reduction mechanism casing in close contact therewith through surface contact at least a part of the inverter to dissipate heat generated from the inverter to the speed reduction mechanism casing. Therefore, heat generated from the inverter can be efficiently transferred and dissipated to the speed reduction mechanism casing with a simple structure. Further, because the inverter is attached to the speed reduction mechanism casing in close contact therewith, no space or member is interposed between the inverter and the speed reduction mechanism casing, and hence the hoisting machine can be constructed in a correspondingly compact form as a whole. 
     In addition, the hoisting machine of the present invention is characterized in that the speed reduction mechanism casing is made of an aluminum material. 
     Thus, the speed reduction mechanism casing is made of an aluminum material having a high thermal conductivity. Therefore, heat generated from the inverter can be dissipated into the surrounding air even more efficiently, and the cooling effect is improved. 
     In addition, the hoisting machine of the present invention is characterized in that the regenerative braking resistor has a resistor casing comprising a corrugated metal plate and a flat metal plate that are superimposed over each other. The corrugated metal plate has an obverse surface with a concave-convex corrugated configuration and a reverse surface with a convex-concave corrugated configuration corresponding to the concave-convex corrugated configuration. Resistance elements are disposed in the concave spaces at the reverse side of the corrugated metal plate of the resistor casing, and an insulating material is filled in the space between the corrugated metal plate and the flat metal plate, including the concave spaces at the reverse side of the corrugated metal plate. 
     Thus, the regenerative braking resistor has resistance elements disposed in the concave spaces at the reverse side of the corrugated metal plate of the resistor casing and further has an insulating material filled in the space between the corrugated metal plate and the flat metal plate, including the concave spaces at the reverse side of the corrugated metal plate. Therefore, the obverse surface of the corrugated metal plate has a wide area, and this obverse surface with a wide area serves as a heat dissipation surface. Accordingly, heat from the resistance elements can be efficiently dissipated. Thus, heat from the regenerative braking resistor can be efficiently dissipated in addition to the advantage that heat from the inverter can be efficiently dissipated as stated above. Therefore, the hoisting machine can be operated at higher frequency than the above. 
     In addition, the hoisting machine of the present invention is characterized in that the corrugated metal plate and flat metal plate of the resistor casing are made of an aluminum material. 
     Thus, the corrugated metal plate and flat metal plate of the resistor casing of the regenerative braking resistor are made of an aluminum material. Because the aluminum material has a high thermal conductivity, it is possible to expect that heat generated from the resistance elements will be effectively dissipated. 
     In addition, the hoisting machine of the present invention is characterized in that the corrugated metal plate of the resistor casing is formed by aluminum die casting. 
     Thus, the corrugated metal plate of the resistor casing of the regenerative braking resistor is formed by aluminum die casting. Because the aluminum die casting process enables the wall thickness of the corrugated metal plate to be increased as compared to pressing, the corrugated metal plate also has the function of lowering the surface temperature of the resistor casing. 
     In addition, the hoisting machine of the present invention is characterized in that the regenerative braking resistor is attached to the casing of the hoisting machine with the flat metal plate of the resistor casing being in abutting contact with the outer surface of the casing of the hoisting machine. 
     Thus, the regenerative braking resistor is attached to the casing of the hoisting machine with the flat metal plate of the resistor casing being in abutting contact with the outer surface of the casing of the hoisting machine. Therefore, the surrounding air is in contact with the surface of the corrugated metal plate of the casing of the regenerative braking resistor. Thus, the heat dissipation action is further promoted. In addition, heat is dissipated from the flat metal plate of the regenerative braking resistor to the surface of the casing of the hoisting machine and dissipated into the surrounding air from the surface of the hoisting machine casing. Therefore, heat dissipation is further promoted. In addition, the casing and the speed reduction mechanism casing are divided from each other by a gasket having a low thermal conductivity. Thus, heat generated from the inverter is dissipated through the speed reduction mechanism casing, while heat generated from the regenerative braking resistor is dissipated directly into the surrounding air and through the surface of the hoisting machine casing. Accordingly, it is possible to control the amount of heat dissipated through each part of the hoisting machine casing surface and hence possible to enhance the overall heat dissipation effect. 
     In addition, the hoisting machine of the present invention is characterized in that the regenerative braking resistor is disposed such that the longitudinal direction of concave grooves constituting the concave-convex corrugated configuration of the corrugated metal plate of the resistor casing is the vertical direction. 
     Thus, the regenerative braking resistor is disposed such that the longitudinal direction of concave grooves constituting the concave-convex corrugated configuration of the corrugated metal plate of the resistor casing is the vertical direction. Consequently, the air heated by the surface of the corrugated metal plate ascends through the concave grooves of the concave-convex corrugated configuration in the form of an ascending current and is released from the upper ends of the concave grooves, and at the same time, the surrounding air flows into the concave grooves from the lower ends thereof, thereby further promoting the heat dissipation action. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention will be explained below with reference to the accompanying drawings.  FIG. 5  is a sectional plan view showing an example of the internal structure of a control box of an electric chain block according to the present invention. As illustrated in the figure, an inverter  12  is attached directly to a speed reduction mechanism casing  15 . In this regard, the inverter  12  and the speed reduction mechanism casing  15  have respective contact surfaces that are flat relative to each other so as to be attached in close contact (surface contact) with each other. The speed reduction mechanism casing  15  is formed by aluminum die casting and contains a lubricating oil (not shown) for lubricating gears and so forth (not shown) constituting a speed reduction mechanism. 
     In a control box  10  are disposed an electromagnetic switch  13  and a transformer  14  that are mounted on a steel panel  11 . When the electric chain block is operated at high frequency, a large amount of heat is generated from the inverter  12  as stated above. The heat is transferred from the inverter  12  to the speed reduction mechanism casing  15  and dissipated into the surrounding air from the speed reduction mechanism casing  15 . The speed reduction mechanism casing  15  is made of an aluminum material having a high thermal conductivity and formed with an increased wall thickness by die casting, as stated above. Therefore, heat generated from the inverter  12  is efficiently transferred to the speed reduction mechanism casing  15  and dissipated into the surrounding air. In addition, the speed reduction mechanism casing  15  contains a lubricating oil and thus forms an oil bath. Therefore, cooling of the inverter by oil cooling can also be expected. Further, because the inverter  12  is attached directly to the speed reduction mechanism casing  15 , the control box  10  can be reduced in size from the size shown by the dotted lines to the size shown by the solid lines (i.e. the overall length of the electric chain block is reduced). 
     Further, the inverter  12  can be efficiently cooled with a very simple structure that the inverter  12  and the speed reduction mechanism casing  15  have respective contact surfaces that are flat relative to each other so as to be attached in close contact with each other. Particularly, the speed reduction mechanism casing  15  does not contain components that generate heat, such as an inverter  12 , a load hoisting motor  41  and a mechanical brake  51  for preventing a fall of a lifted load. In this regard also, effective cooling of the inverter  12  can be expected. 
       FIG. 6  is a sectional plan view showing an example of the overall structure of the electric chain block having the control box  10  arranged as stated above. The electric chain block  20  has a main body casing  21 . The control box  10  is connected to one end of the main body casing  21 , and the inverter  12  in the control box  10  is attached directly to the speed reduction mechanism casing  15 . One end of a motor casing  40  is connected to the other end of the main body casing  21 . A fan cover  50  is connected to the other end of the motor casing  40 . The main body casing  21  houses a chain block main body  22 . The motor casing  40  houses a load hoisting motor  41 . The fan cover  50  covers a fan blade  54  and a lifted-load fall preventing mechanical brake  51 . 
     The chain block main body  22  has a hollow driven shaft  26  and a driving shaft  25  extending through the hollow driven shaft  26 . The hollow driven shaft  26  is rotatably supported through bearings  23  and  24 . The driving shaft  25  is rotatably supported through bearings  34  and  35 . One end of the driving shaft  25  is connected to a rotating shaft  46  of the load hoisting motor  41 . The other end of the driving shaft  25  extends through the hollow driven shaft  26  and has gear teeth formed on the outer periphery of a portion thereof projecting from the hollow driven shaft  26 . The gear teeth are in mesh with a large-diameter intermediate driven gear  27 . The large-diameter intermediate driven gear  27  is fixed to a rotating shaft  28 . The rotating shaft  28  is rotatably supported by the speed reduction mechanism casing  15  through bearings  29  and  30 . The rotating shaft  28  has a small-diameter intermediate driven gear  31  fixed thereto. The small-diameter intermediate driven gear  31  is in mesh with a large-diameter driven gear  32  fixed to the hollow driven shaft  26 . Further, the hollow driven shaft  26  has a load sheave  33  connected thereto. 
     The load hoisting motor  41  has a stator  42  and a rotor  43 . The stator  42  is fitted and fixed in the motor casing  40 . The rotor  43  is fixed to the rotating shaft  46  rotatably supported through bearings  44  and  45 . The rotor  43  extends through the center of the stator  42 . The lifted-load fall preventing mechanical brake  51  has a brake plate  52  fixed to the motor casing  40  and a brake plate  53  fixed to the rotating shaft  46 . When the power supply to the load hoisting motor  41  is cut off, the mechanical brake  51  automatically presses the brake plate  52  against the brake plate  53  with a spring to lock the rotating shaft  46 , thereby preventing a fall of a lifted load. When the power supply is connected to the load hoisting motor  41 , the mechanical brake  51  separates the brake plate  52  from the brake plate  53  against the spring force by the magnetic force of an electromagnet, thereby unlocking the rotating shaft  46 . It should be noted that a fan blade  54  is attached to the end of the rotating shaft  46 . 
     In the electric chain block arranged as stated above, the rotational force of the rotating shaft  46  of the load hoisting motor  41  is transmitted to the driving shaft  25  of the chain block main body  22  and further transmitted to the hollow driven shaft  26  through the large-diameter intermediate driven gear  27  meshed with the gear teeth formed on the driving shaft  25  and further through the small-diameter intermediate driven gear  31  and the large-diameter driven gear  32 . The rotational force transmitted to the hollow driven shaft  26  is transmitted to the load sheave  33  connected to the hollow driven shaft  26  to lift and lower a chain (not shown). That is, the rotational force of the load hoisting motor  41  is transmitted to the hollow driven shaft  26  through a speed reduction mechanism comprising the large-diameter intermediate driven gear  27 , the small-diameter intermediate driven gear  31  and the large-diameter driven gear  32  to rotate the load sheave  33 . It should be noted that the speed reduction mechanism casing  15  contains a lubricating oil (not shown) for lubricating the gear teeth formed on the driving shaft  25 , the large-diameter intermediate driven gear  27 , the small-diameter intermediate driven gear  31  and the large-diameter driven gear  32 , which constitute the above-described speed reduction mechanism. 
       FIG. 7  is a diagram schematically showing the arrangement of a driving circuit for the electric chain block. An electromagnetic switch  60  is closed to turn on the power supply to the inverter  12 , and control signals such as forward rotation, reverse rotation and speed signals are applied to the inverter  12  from a control circuit  61 . Consequently, the load hoisting motor  41  rotates forward (in the direction for lifting a lifted load) or reverse (in the direction for lowering the lifted load) at a specified speed. When the electric chain block is operated at high frequency, i.e. when the operating time of the hoisting machine accounts for 60% or more of the sum total (100%) of the operating time and down time, a large amount of heat is generated from the inverter  12 . In this regard, the inverter  12  is attached directly to the speed reduction mechanism casing  15  as stated above. Accordingly, the heat from the inverter  12  is efficiently dissipated into the surrounding air through the speed reduction mechanism casing  15 , and hence the inverter  12  is effectively cooled. In addition, the speed reduction mechanism casing  15  contains a lubricating oil and thus forms an oil bath, as stated above. Therefore, the inverter  12  is also oil-cooled. Thus, even if the hoisting machine is operated at high frequency, the inverter  12  will not heat up to a predetermined trip temperature (e.g. 100° C.) or more and thus can avoid being tripped. 
     In addition, as shown in  FIG. 6 , a regenerative braking resistor  70  is attached to a side of the control box  10 . When the load hoisting motor  41  lowers the lifted load, it functions as a generator, and a regenerative electric current generated in this way is passed through the regenerative braking resistor  70  and thus consumed, thereby regeneratively braking the load hoisting motor  41 . In addition, during the operation of the load hoisting motor  41 , the fan blade  54  rotates to send air to the lifted-load fall preventing mechanical brake  51  and the load hoisting motor  41  to cool them. 
       FIG. 8  is a diagram showing an example of the structure of the regenerative braking resistor  70 .  FIG. 8(   a ) is a plan view.  FIG. 8(   b ) is a front view.  FIG. 8(   c ) is an A-A sectional view. As illustrated in these figures, the regenerative braking resistor  70  has a casing  71  comprising a corrugated metal plate  72  and a flat metal plate  73 . The corrugated metal plate  72  is formed by die casting of an aluminum material to have an obverse surface with a concave-convex corrugated configuration and a reverse surface with a convex-concave corrugated configuration corresponding to the concave-convex corrugated configuration. The height H 1  of two opposite sides of the corrugated metal plate  72  is greater than the height H 2  of the concave-convex corrugated portion thereof (H 1 &gt;H 2 ). The flat metal plate  73  is formed from a flat aluminum material. The corrugated metal plate  72  and the flat metal plate  73  are superimposed over each other to constitute the casing  71 . 
     Resistance elements  74  are disposed in the concave spaces  75  at the reverse side of the corrugated metal plate  72  of the casing  71 , and an insulating filler  76  is filled in the space between the corrugated metal plate  72  and the flat metal plate  73 , including the concave spaces  75 . As the insulating filler  76 , a heat-resisting cement, e.g. heat-resisting silicone cement, is used. Regarding joining of the corrugated metal plate  72  and the flat metal plate  73 , the flat metal plate  73  is secured to the corrugated metal plate  72  by threading screws  77  into the corrugated metal plate  72  through the flat metal plate  73 . A plurality of resistance elements  74  are electrically connected in series, and lead terminals  80  for supplying an electric current to the resistance elements  74  are led out from one side of the casing  71 . 
     The resistance elements  74  may be any type of resistance element that can efficiently convert an electric current passed therethrough into heat. An example of usable resistance elements comprises, as shown in  FIG. 9 , a columnar member (or cylindrical member)  78  made of a heat-resisting insulating material, e.g. a ceramic material, and a resistance wire  79 , e.g. a nichrome wire, wound around the columnar member  78 . 
     With the above-described structure of the regenerative braking resistor  70 , when an electric current is passed through the resistance elements  74 , heat generated therefrom is transferred to the corrugated metal plate  72  made of an aluminum material of good thermal conductivity through the insulating filler  76 . The corrugated metal plate  72  has its obverse surface formed into a concave-convex corrugated configuration to have a wide surface area and hence efficiently dissipates the transferred heat into the surrounding air. Further, because the corrugated metal plate  72  is formed by aluminum die casting, the wall thickness thereof can be increased as compared to pressing. Accordingly, the corrugated metal plate  72  has the advantageous effect of lowering the surface temperature. 
     As shown in  FIG. 10 , the regenerative braking resistor  70  is attached to the outer side surface of the control box  10 . An electric current generated by the load hoisting motor  41  during lowering of a lifted load is passed through the resistance elements  74  of the regenerative braking resistor  70 , and heat generated from the resistance elements  74  at this time is transferred to the corrugated metal plate  72  of an aluminum material through the insulating filler  76 . The corrugated metal-plate  72  of the regenerative braking resistor  70  is formed by aluminum die casting to have an obverse surface with a concave-convex corrugated configuration as stated above. Therefore, the corrugated metal plate  72  has a wide surface area and is therefore capable of efficiently dissipating the heat from the resistance elements  74 . Because the corrugated metal plate  72  is formed by aluminum die casting, in particular, the wall thickness of the corrugated metal plate  72  can be increased as compared to pressing. Thus, the corrugated metal plate  72  also has the advantageous effect of lowering the surface temperature. 
     The control box  10  and the speed reduction mechanism casing  15  are divided from each other by a gasket  16  of low thermal conductivity. The installation position of the gasket  16  of low thermal conductivity is properly changed according to the amount of heat generated from the inverter  12  attached to the speed reduction mechanism casing  15 , the high-temperature performance of the inverter  12 , the amount of heat generated from the regenerative braking resistor  70  attached to the control box  10 , and so forth, thereby controlling the amount of heat dissipated from each part of the electric chain block casing surface and the range of conduction of heat. Among the components, the regenerative braking resistor  70  generates heat most. Therefore, an effective practice is to increase the surface area of the electric chain block casing for dissipating the heat generated from the regenerative braking resistor  70 . It is, however, not preferable from the viewpoint of the heat resistance of the inverter  12  that the heat of the regenerative braking resistor  70  influence the inverter  12  attached to the speed reduction mechanism casing  15 . It is also necessary to dissipate the heat generated from the inverter  12  from the surface of the electric chain block casing. Therefore, in a case where the inverter  12  has high heat resistance and generates a relatively small amount of heat, the gasket  16  is installed at a position at which the surface area of the control box  10  is widened. In a case where the inverter  12  has low heat resistance or generates a relatively large amount of heat, the gasket  16  is installed at a position at which the surface area of the control box  10  is narrowed and the surface area of the speed reduction mechanism casing is correspondingly widened. By so doing, the overall heat dissipation performance of the hoisting machine can be effectively improved. It should be noted that  FIG. 10  is an enlarged view of a part of  FIG. 6  that shows the control box  10 . 
       FIG. 11  is an enlarged view of a part of the electric chain block according to the present invention, showing another example of the internal structure of the control box  10 . As illustrated in the figure, a recess  81  is formed on a side of the control box  10 , and a regenerative braking resistor  70  serving as a braking resistance is disposed in the recess  81 . The opening of the recess  81  is covered with a plate member  82  having a plurality of slits  82   a  as shown in  FIG. 12 . With the arrangement in which the regenerative braking resistor  70  is disposed in the recess  81  formed on the side of the control box  10 , the regenerative braking resistor  70  does not project from the side of the control box  10  unlike the arrangement shown in  FIG. 10 . Accordingly, the external appearance is improved. 
     Here, as shown in  FIG. 13 , the regenerative braking resistor  70  is disposed such that the concave grooves  72   a  of the corrugated metal plate  72  extend in the vertical direction, and vertical grooves  10   a  are formed on the upper and lower edges of the recess  81  of the control box  10 . Thus, air A flowing in through the grooves  10   a  formed on the lower edge of the recess  81  enters the space between the plate member  82  and the corrugated metal plate  72  (see  FIG. 11 ) where the air A is heated by heat radiated from the surface of the corrugated metal plate  72 . The heated air A ascends through the concave grooves  72   a  in the form of an ascending current and flows out through the grooves  10   a  formed on the upper edge of the recess  81 . At the same time, cold fresh air flows in from the lower side. Thus, the cooling effect is further promoted. It should be noted that  FIG. 13  is a diagram showing a side surface of the control box  10  with the plate member  82  removed therefrom. 
     The resistance elements  74  of the regenerative braking resistor  70  are disposed in the concave spaces  75  at the reverse side of the corrugated metal plate  72  of the casing  21 , as stated above. Regarding the installation position thereof, the resistance elements  74  may be positioned in the respective openings of the concave spaces  75  as shown in  FIG. 14(   a ), or in the respective upper portions of the concave spaces  75  as shown in  FIG. 14(   b ), or directly below the respective concave spaces  75  as shown in  FIG. 14(   c ). Among these positions, the best heat dissipation effect was obtained when the resistance elements  74  were positioned in the respective openings of the concave spaces  75  as shown in  FIG. 14(   a ). 
     With the electric chain block, the control box  10  was arranged as shown in  FIG. 11 , and the regenerative braking resistor  70  was formed by using a resistor having resistance elements  74  disposed at the respective positions shown in  FIG. 14(   a ). The electric chain block was operated at high frequency to measure the following various temperatures when the saturation temperatures were reached: the surface temperature A of the speed reduction mechanism casing  15 ; the outer wall surface temperature B of the control box  10 ; the surface temperature C of the corrugated metal plate  72  of the regenerative braking resistor  70 ; the temperature D at the bottom of the concave grooves  72   a ; and the surface temperature E of the speed-reduction mechanism casing  15  at a part thereof where the inverter  12  is attached. The measurement results were all satisfactory. Thus, the electric chain block was proved to be capable of performing high-frequency operation. 
     Although an embodiment of the present invention has been described above, the present invention is not limited to the foregoing embodiment but can be modified in a variety of ways without departing from the scope of the claims and the technical idea indicated in the specification and the drawings. For example, although in the foregoing embodiment an electric chain block has been described as a hoisting machine, by way of example, the hoisting machine according to the present invention may be an electric hoist that winds up and unwinds a wire rope on and from a drum. 
     Further, in the foregoing embodiment, the heat dissipation means that dissipates heat generated from the inverter  12  to the speed reduction mechanism casing  15  is a means for attaching the inverter  12  directly to the speed reduction mechanism casing  15  in close contact therewith to dissipate heat generated from the inverter  12  to the speed reduction mechanism casing  15 . The heat dissipation means is not limited thereto. For example, a heat transfer means, e.g. a heat pipe, may be used to transfer heat generated from the inverter  12  to the speed reduction mechanism casing  15 . The use of another heat transfer means or a combination of the heat dissipation means and another heat transfer means is effective particularly when the inverter cannot be attached directly to the speed reduction mechanism casing, or when a wide part of the side wall of the inverter cannot be attached directly to the speed reduction mechanism casing. 
     INDUSTRIAL APPLICABILITY 
     The hoisting machine according to the present invention dissipates heat generated from the inverter to the speed reduction mechanism casing. Therefore, it is possible to effectively dissipate heat generated from the inverter into the surrounding air through the speed reduction mechanism casing having a large heat capacity. Further, because the speed reduction mechanism casing contains a lubricating oil and hence forms an oil bath, it is also possible to expect cooling of the inverter by oil cooling. Accordingly, the invention of this application can provide an inverter-incorporating hoisting machine capable of performing high-frequency operation. 
     The hoisting machine according to the present invention uses, as a regenerative braking resistor, a resistor in which resistance elements are disposed in concave spaces at the reverse side of a corrugated metal plate constituting a resistor casing and an insulating material is filled in the space between the corrugated metal plate and the associated flat metal plate, including the concave spaces at the reverse side of the corrugated metal plate. Thus, the corrugated metal plate provides a wide surface area, and the corrugated metal plate surface having a wide area serves as a heat dissipation surface. Therefore, heat from the resistance elements can be dissipated effectively. Accordingly, heat from the regenerative braking resistor can be efficiently dissipated in addition to the advantage that heat from the inverter can be efficiently dissipated as stated above. Thus, the invention of this application can provide an inverter-incorporating hoisting machine capable of performing high-frequency operation. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional plan view showing the internal structure of a control box of a conventional electric chain block. 
       FIG. 2  is a sectional plan view showing the internal structure of a control box of a conventional electric chain block. 
       FIG. 3  is a diagram showing a structural example of a regenerative braking resistor of a conventional hoisting machine, of which:  FIG. 3(   a ) is a plan view;  FIG. 3(   b ) is a front view; and  FIG. 3(   c ) is a right-hand side view. 
       FIG. 4  is a diagram showing a structural example of a regenerative braking resistor of a conventional hoisting machine, of which:  FIG. 4(   a ) is a plan view; and  FIG. 4(   b ) is a front view. 
       FIG. 5  is a sectional plan view showing an example of the internal structure of a control box of an electric chain block according to the present invention. 
       FIG. 6  is a sectional plan view showing an example of the overall structure of the electric chain block according to the present invention. 
       FIG. 7  is a diagram schematically showing the configuration of a driving circuit for the electric chain block. 
       FIG. 8  is a diagram showing a structural example of a regenerative braking resistor of the electric chain block according to the present invention, of which:  FIG. 8(   a ) is a plan view;  FIG. 8(   b ) is a front view; and  FIG. 8(   c ) is an A-A sectional view. 
       FIG. 9  is a diagram showing a structural example of a resistance element. 
       FIG. 10  is a sectional plan view showing another example of the internal structure of the control box of the electric chain block according to the present invention. 
       FIG. 11  is a sectional plan view showing still another example of the internal structure of the control box of the electric chain block according to the present invention. 
       FIG. 12  is a diagram showing the external shape of a cover for the regenerative braking resistor of the electric chain block according to the present invention. 
       FIG. 13  is a diagram showing the position where the regenerative braking resistor is installed in the control box of the electric chain block according to the present invention. 
       FIG. 14  is a diagram showing the installation position of resistance elements in a resistor casing of the regenerative braking resistor of the electric chain block according to the present invention. 
     LIST OF REFERENCE SIGNS 
       10 : control box 
       11 : panel 
       12 : inverter 
       13 : electromagnetic switch 
       14 : transformer 
       15 : speed reduction mechanism casing 
       16 : gasket 
       20 : electric chain block 
       21 : main body casing 
       22 : chain block main body 
       23 : bearing 
       24 : bearing 
       25 : driving shaft 
       26 : hollow driven shaft 
       27 : large-diameter intermediate driven gear 
       28 : rotating shaft 
       29 : bearing 
       30 : bearing 
       31 : small-diameter intermediate driven gear 
       32 : large-diameter driven gear 
       33 : load sheave 
       34 : bearing 
       35 : bearing 
       40 : motor casing 
       41 : load hoisting motor 
       42 : stator 
       43 : rotor 
       44 : bearing 
       45 : bearing 
       46 : rotating shaft 
       50 : fan cover 
       51 : lifted-load fall preventing mechanical brake 
       52 : brake plate 
       53 : brake plate 
       54 : fan blade 
       60 : electromagnetic switch 
       61 : control circuit 
       70 : regenerative braking resistor 
       72 : corrugated metal plate 
       73 : flat metal plate 
       74 : resistance element 
       75 : concave space 
       76 : insulating filler 
       77 : screw 
       78 : columnar member (or cylindrical member) 
       79 : resistance wire 
       80 : lead terminal 
       81 : recess 
       82 : plate member