Electric noise absorber

Abstract: An electric noise absorber for clamping to a cord of an electronic device comprises a holding case (1) composed of two box-shaped case members (2,3). Each case member (2,3) contains a magnet having a hemi-cylindrical groove at the upper part of the magnet for receiving the cord. It is possible to easily and securely attach and detach the electric noise absorbing magnet to the cord by simply closing and opening the case members (2,3).

Description: Technical field The invention relates to an electric noise absorber according to the first part of daim 1 for absorbing electric noise which is generated within an electronic device or which enters from the outside into the device through a cord. Background art As a method for absorbing such noise, it is well-known that magnetic ferrite can be attached to a cord. Thereby two pieces of half ring-shaped ferrite are attached by adhesive tape around the cord or according to JP-A-6016404 by grooves and protrusions formed in the contact surfaces of the two pieces. However the pieces are apt to easily come off from the cord because the protrusion may slip out from the groove. Furthermore the conductive ferrite may make a short circuit or may generate a contact electricity in the electronic device. EP-A-01 89 240 shows two case members of a splice case containing a gel for protecting a substrate from the environment effects such as moisture. Problems in connection with an electric noise absorber containig two members of magnetic substance cannot be solved by this splice case. JP-A-6214770 shows a noise absorber having stripe-like case members for holding two ferrite members together and around a cord. The ferrite members are fixed to the case members by an adhesive. When the case members are closed and locked by hooks on one side the ferrite members abut against each other, however, these hooks are merely able to urge the ferrite halves together on the side of the hooks and on the other side, where the case members are connected by a hinge a clearance can occur or at least the members of ferrite cannot be pressed closely together. The result is a deterioration of the noise absorbing ability. Moreover, it is not possible to replace a magnetic member when breaking. DISCLOSURE OF THE INVENTION It is therefore the object of the invention to provide an electric noise absorber comprising two members of magnetic substance which are held securely and detachable in the case members thereby preventing any short circuit or electrical contact with other conductive parts. To solve this problem the electric noise absorber according to the invention includes the features of claim 1. The members of magnetic substance have merely to be inserted in the case members and then the flexible projections automatically secure the respective members of magnetic substance by snapping in the notches. To detach the member of magnetic substance the projections merely have to be bent outwardly. The biassing means are able to bias the members of magnetic substance closely together around the cord and therefore, this noise absorber can effectively absorb electric noise and prevent the inflow of noise. The noise absorber can be easily attached to and detached from the cord whenever required. The members of magnetic substance can be replaced in the open state of the two case members. BRIEF DESCRIPTION OF DRAWINGS This invention is illustrated diagrammatically in the following drawings wherein: Fig. 1 is a perspective view illustrating a holding case 1 of the first embodiment; Fig. 2 is a plan view of the holding case 1 shown in Fig. 1; Fig. 3 is a left side view of the holding case 1 shown in Fig. 1; Fig. 4 is a front view of the holding case 1 shown in Fig. 1; Fig. 5 is a bottom view of the holding case 1 shown in Fig. 1; Fig. 6 is a rear view of the holding case 1 shown in Fig. 1; Fig. 7 is a sectional view taken along line VII-VII of Fig. 2; Fig. 8 is a sectional view taken along line VIII-VIII of Fig. 2; Fig. 9 is a sectional view taken along line IX-IX of Fig. 2; Fig. 10 is a sectional view taken along line X-X of Fig. 2; Fig. 11 is a perspective view illustrating a ferrite member 5; Fig. 12 is a perspective view when an electric noise absorber is attached to a cord 30; Fig. 13 is a left side view illustrating the absorber attached to the cord 30; and Fig. 14 is a perspective view illustrating a case member 22 of the second embodiment. BEST MODE FOR CARRYING OUT OF THE INVENTION The first embodiment of this invention will be described with reference to Figs. 1 through 13. Fig. 1 shows a perspective view of a holding case 1 of an electric noise absorber. The holding case 1 is composed of two case members 2 and 3 connected by means of two hinges 4. The case members 2 and 3 are box-shaped with one open surface and formed so as to securely contain a ferrite member 5 shaped as shown in Fig. 11. Four biassing members 6 and 7 project resiliently inward from the bottom of the case members 2 and 3 for biasing the ferrite member 5. Wide fixing members 8 and 9 are provided at the center of the front surface (the surface shown in Figs. 4 and 6) of the case members 2 and 3 for securing an upper side of the ferrite member 5. Two pairs of flexible supporting projections 10 and 11 are formed adjacent to the fixing members 8 and 9. Within the case member 2, a pair of supporting projections 15 projects inward from a surface opposite to the projections 10. Within the case member 3, a pair of supporting projections 16 projects inward from a surface opposite to the projections 11. The projections 10, 11, 15 and 16 project inward from the front surface so as to support side notches 5a of the ferrite member 5. Moreover, long engaging tabs 12 are provided adjacent to the projections 10 of the case member 2. Engaging projections 13 and protrusions 14 are provided adjacent to the projections 11 of the case member 3. The projections 13 are engaged with the tabs 12 when the holding case 1 is closed. Substantially semi-holes 17 having teeth 17a are formed on both side walls of the case member 2 for inserting a cord. Likewise, semi-holes 18 having teeth 18a are formed on both side walls of the case member 3. A shown in Fig. 11, a hemi-cylindrical groove 5b is formed longitudinally along the upper part of the ferrite member 5 for receiving the cord. The notches 5a are formed on both sides of the ferrite member 5. The holding case 1 is integrally formed of a synthetic resin, and each member, projection and tab have appropriate resilience. Two ferrite members 5 are contained in the case members 2 and 3 of the holding case 1. In the case member 2, the upper side of the ferrite member 5 is secured by the fixing member 8. Two pairs of supporting projections 10 and 15 engage with the notches 5a, therefore the ferrite member 5 is securely held in the member 2. Likewise, in the case member 3, the upper side of the ferrite member 5 is secured by the fixing member 9, and two pairs of the projections 11 and 16 engage with the notches 5a. Thus the ferrite member 5 is securely held within the case member 3. In the state that the ferrite members 5 are contained in the case members 2 and 3, a cord 30 is inserted between the case members 2 and 3, and the case member 3 covers the case member 2 so that the case 1 is attached to the cord 30 of an electronic device. The engaging projections 13 of the case member 3 are engaged with the engaging tabs 12 of the case member 2, therefore the case 1 is securely fastened. When the case 1 is closed, the biassing members 6 and 7 projecting from the bottom of the case members 2 and 3 support the ferrite members 5 so as to join them together, thereby, the ferrite members 5 are securely held. As shown in Fig. 13, the teeth 17a and 18a, around the semi-holes 17 and 18 formed on both side walls of the case members 2 and 3, are clamped against the cord 30. By applying an appropriate number of the holding cases 1 containing the magnetic ferrite members 5 to the cord 30, noise flowing in the cord 30 is absorbed by the magnetic ferrite and generation of noise is prevented. The noise absorbing efficiency of the case 1 is measured at various positions thereof along the cord by a noise measuring device, and the position for the case where noise is absorbed most efficiently is found. It is preferable that the most appropriate number of the cases to be used are experimentally determined by measuring the noise absorbing efficiency. The ferrite members 5 absorb noise that is generated outside or enters the electronic device through the cord. To detach the case from the cord or to change its position thereon, the engaging tabs 12 of the case member 2 are pulled outwardly so that the tabs 12 detach easily from the engaging projections 13 and the case 1 can be opened. It is possible to secure the holding case 1 to a circuit board with a double-sided adhesive tape. As shown by a double-dash interrupted line in Fig. 6, a mounting leg 31 having an engaging hook may be attached to the bottom of the case member 2 or 3 so as to secure the holding case to the circuit board. Regarding the magnetic substance, either hard or soft ferrite can be used. Further, a plastic magnet or rubber magnet which is made by mixing magnetic powder of ferrite with plastic or rubber can also be used. The second embodiment of this invention is shown in Fig. 14. In this embodiment, an engaging tab 112 and a projection 113 are formed on each of the sides of a single case member 22. Another projection 113 is also provided opposite to the engaging tab 112. In order to secure the cord 30, two same case members 22 are prepared, and one ferrite member 5 is contained in each case member. Then the cord 30 is held between a pair of case members 22 and the engaging tab 112 is engaged with the projection 113. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims in the invention may be practiced otherwise than as specifically described.

Claims: An electric noise absorber for surrounding a cord (30) of an electronic device comprising two members of magnetic substance (5), being mutually opposed in register and in contact when the absorber is in use, each having a hemi-cylindrical groove for receiving the cord (30), characterized by two box-shaped case members (2, 3; 22) each with one open surface for covering the cord (30) when interlocked, each case member (2, 3; 22) containing said each member of magnetic substance (5), wherein said each case member (2,3;22) has biassing means (6,7) on a surface opposite to the open surface for biassing the member of magnetic substance (5) to the cord (30) when the case members (2, 3; 22) are closed and/or wherein each said member of magnetic substance (5) has notches (5a) and each said case member (2, 3; 22) has flexible projections (10, 11, 15, 16) for securing the member of magnetic substance (5) in the case member (2, 3; 22) by engaging with the notches (5a). The electric noise absorber according to claim 1, wherein one of the case members (3) has a hook (31) projecting outside of the case member (3) on the surface opposite to the open surface for securing the case to a circuit board. The electric noise absorber according to claim 1 or 2, wherein each case member (2, 3; 22) being box-shaped with one open surface, wherein a semi-hole (17,18) is formed on each of narrow edges of the open surface for passing the cord (30). The electric noise absorber according to claim 3, wherein teeth (17a, 18a) are formed on an edge of each of the semi-holes (17, 18) for securing the cord (30) when the case members (2, 3;22) are closed. The electric noise absorber according to claim 3 or 4, wherein the two case members (2, 3) form halves of one body and are connected by a hinge (4) and each said case member (2, 3) has means (12, 13) for engaging with the other such that the case members (2, 3) clamp around the cord (30). The electric noise absorber according to claim 5, wherein the hinge (4) is formed along a longitudinal edge of the open surface and the engaging means (12, 13) are formed on another longitudinal edge of the open surface. The electric noise absorber according to claim 3 or 4, wherein the two case members (22) are formed separately and same to each other and said each case member (22) has means (112, 113) for engaging with each other such that the case members (22) clamp around the cord (30). The electric noise absorber according to claim 7, wherein the engaging means (112, 113) are formed along a longitudinal edge of the open surface.

Inventors: NAKANO YOSHIHITO, NAKANO, YOSHIHITO
Applicants: KITAGAWA IND CO LTD, KITAGAWA INDUSTRIES CO., LTD.
Application year: 1987
Main classification: H03H1
IPC codes: H03H1, H01F27, H01F17