1. Field of the Invention
The present invention relates to a casing structure for electronic equipment that has the effect of shielding electromagnetic waves. More particularly, the present invention relates to a casing structure for electronic equipment that has the effect of shielding electromagnetic waves by means of electrical grounding between a case member and an electronic equipment support member that serves to support electronic boards and the like when the electronic equipment support member is mounted in the case member
2. Background Information
Due to improvements in electronics technology, the use of electronic equipment, consumer electronics, communications equipment, and the like are becoming increasingly common in our daily lives. However, these devices continually generate electromagnetic waves when electrical power is supplied to them. In particular, the increase in the speed of the process and the colorization in recent image forming devices (e.g., digital copying machines, printers, and the like) is one cause of many of the electromagnetic waves generated by various devices arranged inside an image forming device. The electromagnetic waves generated by these devices are capable of having an adverse impact on other circuits in the devices and on other external electronic equipment, and thus there is a need to prevent the exterior leakage of electromagnetic waves to the greatest degree possible.
Control at a high clock frequency is needed in order to increase the speed of the process in an image forming device. When this occurs, strong electromagnetic waves may be generated from the control board or the like that generates the high clock frequency. For example, with a digital copying machine, multiple overlap of signal forms that are synchronized with the clock frequency will occur due to the relationship between high speed original document scanning and image formation when these are simultaneously performed, and thus will cause even stronger electromagnetic radiation. In addition, with recent color copying machines and printers, electromagnetic waves in an even higher frequency band may be generated at a high intensity due to the overlap of the clock frequency of a charge coupled device control board that is color separated into at least four colors, the increase in speed, and the improvement in image quality (high density pixels). Because of these issues, countermeasures against the strong electromagnetic waves that leak from image forming devices are in urgent demand. For example, electromagnetic wave shielding for the leakage of electromagnetic waves in the 30 to 230 MHz range is now being studied by groups such as the Voluntary Control Council of Japan For Interference By Information Technology Equipment (VCCI). However, the countermeasures for the electromagnetic wave shielding must respond to recent demands for lower cost equipment, and thus it is desirable that the electromagnetic wave shielding maintain superior electromagnetic wave shielding effects while performing the shielding with the most inexpensive means possible.
Various types of electromagnetic shielding for electronic equipment have been tried in the past. One example of these is a conductive flexible member that is attached to an image forming device as a grounding member (see, for example, Japanese unexamined patent application publication H5-307282). With Japanese patent application publication H5-307282, one end of the conductive flexible member is attached to the main portion of the electronic equipment with a screw, and when the electronic equipment is grounded, the plate spring effect of the flexible member will be used to press the other end of the flexible member to be in contact with another member.
In another example, an elastic conductive member is used as an electromagnetic shielding material, and attached to the contact portions between the support members and frame of electronic equipment to prevent the leakage of electromagnetic waves (see, for example, Japanese unexamined patent application publication H6-291485). With Japanese unexamined patent application publication H6-291485, a conductive sponge is adhered to the contact portions between the support members and case member with a double-sided adhesive tape, the portions of the support members and the case member that are out of range of the adhesive area of the double-sided adhesive tape are brought into contact with each other, and the electrical contact of both is thereby achieved.
In another example, an image reading device in which the end portions of a board are bent, and contact pressure is produced on the decorative case of a device during board mounting in order to perform grounding (see, for example, Japanese unexamined patent application publication H6-105080).
In addition, other examples include an image forming device in which 2 units are brought into contact via a conductive elastic member (see, for example, Japanese unexamined patent application publication H8-190237), and a structure in which a shielding cover covers the upper portion of an electromagnetic noise generation source (see, for example, Japanese unexamined patent application publication 2002-237915).
However, with the grounding configuration of the image forming device that is disclosed in Japanese unexamined patent application publication H5-307282, it will be necessary to newly provide a grounding member for electromagnetic shielding in the image forming device, and it will also be necessary to fix the grounding member in the image forming device with a large number of screws or the like. Because of this, the number of parts and steps needed during the assembly of the grounding structure of the image forming device disclosed in this reference will increase, the assembly efficiency of the image forming device will worsen, and manufacturing costs will increase.
With the electromagnetic wave prevention device disclosed in Japanese unexamined patent application publication H6-291485, double-sided adhesive tape is employed to fix the conductive sponges, but even with this construction, a new and separate member for electromagnetic wave shielding is fixed with a fixing means (double-sided tape), and thus the previously noted problems of worsened assembly efficiency due to the increase in the number of parts and assembly steps, and the increase in manufacturing costs, will not be solved.
With the image reading device disclosed in Japanese unexamined patent application publication H6-105080, if there is an increase in emission waves from the board, the equipment inside the device will malfunction due to this increase, the ends of the board will become antennas, and electromagnetic waves will be easily emitted to the exterior of the device. Furthermore, with Japanese unexamined patent application publication H6-105080, although electrical connectivity is achieved by bending the ends of the board, the opposite sides of the bend portions are fixed with screws, and thus this construction cannot contribute to the elimination of parts and a simplified assembly.
Furthermore, even with the devices of Japanese unexamined patent application publication H8-190237 and Japanese unexamined patent application publication 2002-237915, there will be problems with the ease of assembly, the cost aspect, and the workability thereof, and thus there is a great deal of room for improvement.
Thus, an object of the present invention is to take these problems into consideration, and provide a casing structure for electronic equipment in which the assembly of the electronic equipment is simplified while providing both a grounding effect and an electromagnetic wave shielding effect, and in which the low cost manufacture of the electronic equipment can be achieved.