Patent Application
20120115335
1. Field of the Invention
The present invention relates to a slip ring device and more specifically to a slip ring device preferably for use in transmitting signals in a mechanism including a swing unit, such as, for example, a monitoring camera or a robot mechanism.
2. Description of the Related Art
A conventional slip ring device extensively used in flexing portions or rotating portions such as joint portions of an industrial robot can maintain connection and electric conduction between a fixed-side wiring line and a rotating-side wiring line at all times regardless of continuous rotation or reverse rotation. The slip ring device is designed to avoid disconnection of a wiring line otherwise caused by complex layout or bending fatigue. More specifically, as shown in FIGS. 11 and 12 of Japanese Patent Application Publication No. 2003-116249, a known slip ring device includes a rotating shaft unit having a rotating shaft and a plurality of electricity-collecting rings fixed to the rotating shaft and a fixed unit having a case and electrically conductive brushes and terminals, both of which are connected to the case. Lead lines connected to the electricity-collecting rings are led out to the outside through an insertion bore of the rotating shaft. The electrically conductive brushes connected to the terminals of the fixed unit are kept in sliding contact with the electricity-collecting rings at all times, thereby electrically interconnecting the shaft-side lead lines and the case-side terminals.
In the meantime, a monitoring camera is used as an image signal input unit in a warning system for crime and disaster prevention. A slip ring is arranged on a support base for rotatably supporting the monitoring camera, so that signals can be transmitted between the monitoring camera and the support base through the slip ring. For instance, Japanese Patent Application Publication No. 2005-278071 discloses a known slip ring coupling structure for a monitoring camera and a structure for rotatably and concentrically coupling a first rotating shaft within a slip ring attached to a base plate with a second rotating shaft fixed to a camera support base.
In recent years, due to the demand for an increased image quality, a high-definition monitoring camera is available in a monitoring camera market. In the state-of-the-art monitoring cameras, image information of 200,000 to 400,000 pixels is transmitted at a transmitting speed of about 100 Mbps. In the high-definition monitoring camera of the kind stated above, there is a need to rapidly transmit high-definition image data of 1,000,000 pixels or more, or full-high-definition image data of 2,000,000 pixels or more, at a transmitting speed of about 1 Gbps or more. The conventional slip ring device mentioned above has a structure in which the lead lines are just electrically connected to the brushes and the electricity-collecting rings making sliding contact with each other at all times. Three signal transmission routes, i.e., a lead line route, a slip ring route and a lead line route, are just serially connected to one another with no consideration given to impedance consistency. Therefore, high-speed high-frequency signals such as image signals of a high-definition camera are reflected in the joints of the signal transmission routes and thus are not smoothly transmitted through the signal transmission routes. This leads to increased signal attenuation and reduced reliability.
Preferred embodiments of the present invention provide a slip ring device that can be used in high-speed transmission of signals of a high-definition monitoring camera or a full-high-definition monitoring camera.
In accordance with a preferred embodiment of the present invention, a slip ring device preferably includes a hollow pipe-shaped shaft rotatably supported inside a tubular body of a main case through a bearing; an electricity-collecting body concentrically provided on the shaft, the electricity-collecting body including a plurality of electricity-collecting rings and a plurality of insulating rings alternately layered with one another; a plurality of brushes provided in a corresponding relationship with the electricity-collecting rings, the brushes including base portions held by the main case and tip end portions arranged to make sliding contact with outer circumferential surfaces of the electricity-collecting rings; and a plurality of lead lines introduced into the shaft, the lead lines including tip end portions electrically connected to the respective electricity-collecting rings, the lead lines including two or more shielded lines.
Two or more of the lead lines electrically connected to the electricity-collecting rings of the electricity-collecting body include twisted-pair lines (preferably including shielding). This makes it possible to make the signals transmitted through the lead lines less susceptible to noises, thereby reducing the amount of radiating noises. If the impedance of the twisted-pair lines is matched with the impedance of slip rings as close as possible, it is possible to reduce reflection of signals caused by the mismatching of impedances and to reduce degradation of signals. As a result of this specific arrangement, it becomes possible to transmit high-speed high-frequency signals, such as, for example, image signals of a high-definition camera. Accordingly, the slip ring device can be included in, for example, a high-definition monitoring camera or other suitable apparatus. The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
A slip ring device according to preferred embodiments of the present invention will now be described with reference to the accompanying drawings.
An annular flange portion 16a is provided at one end portion of the shaft 16 to make contact with the end surface of an inner race of one bearing 12 from one axial end of the shaft 16. A thread portion 16b is defined on the outer circumferential surface of the other end of the shaft 16. From the other end side of the shaft 1b, a yoke 18 is fitted to the shaft 16, and a nut 20 is threadedly coupled to the thread portion 16b of the shaft 16. Thus, a ring-shaped protrusion 18a protruding from the central area of the yoke 18 presses an inner race of the other bearing 14 at the axial outer side, thereby applying a pre-compression force to the bearings 12 and 14 arranged between the tubular body 10 and the shaft 16. As a result, the shaft 16 is rotatably and stably supported with respect to the main case with no likelihood of looseness.
The yoke 18 is provided with a recess portion 18b at the other side thereof. The nut 20, when tightened, is accommodated within the recess portion 18b and is prevented from protruding beyond the end surface of the yoke 18. The yoke 18 has a thread hole 18c radially extending therethrough. A stopper screw 22 is threadedly fastened to the thread hole 18c so that the end surface of the stopper screw 22 can be pressed against the shaft 16. Thus, the yoke 18 is fixed to the shaft 16. In this manner, the tubular body 10 of the main case and the shaft 16 are rotatably coupled with each other.
An electricity-collecting body 24 is provided at one end of the shaft 16 to protrude from the shaft 16. As shown in
The rib plates 26c of the holder 26 are inserted through the bores of the electricity-collecting rings 28 and the insulating rings 30. More specifically, six electricity-collecting rings 28 and six insulating rings 30 are alternately layered from the end plate 26a. A cylindrical bush 32 is preferably fitted to the other end portion of the holder 26. Thus, the electricity-collecting rings 28 and the insulating rings 30 are interposed between the end plate 26a and the bush 32 in a layered state, thereby defining the electricity-collecting body 24. When the electricity-collecting body 24 is in an assembled state, the electricity-collecting rings 28, which are smaller in diameter than the end plate 26a and the insulating rings 30, are positioned between the end plate 26a and the respective insulating rings 30. A plurality of brushes (to be described in detail later) makes sliding contact with the outer circumferential surfaces of the respective electricity-collecting rings 28 under a suitable contact pressure. At this time, the brushes are kept in position by the end plate 26a and the respective insulating rings 30 without axially moving out of contact with the electricity-collecting rings 28. The electricity-collecting body 24 is securely fixed to the shaft 16 by fitting the bush 32 to the opening of one end portion of the shaft 16.
A lead line group 34 including a plurality of lead lines defining a first transmission route is connected to the respective electricity-collecting rings 28 of the electricity-collecting body 24. More specifically, conical surfaces are defined in the inner circumferences of the respective electricity-collecting rings 28. The end portions of core wires of the lead lines are electrically connected to the conical surfaces of the respective electricity-collecting rings 28 preferably by, for example, laser welding, soldering, etc. The lead lines connected to the respective electricity-collecting rings 28 pass between the respective rib plates 26c and extend through the shaft 16 to a location outside the shaft 16.
By this arrangement, the two electricity-collecting rings 28 arranged closer to the base portion (more specifically, closer to the bush 32) of the electricity-collecting body 24 are preferably arranged to be used for high-frequency signals. The remaining four electricity-collecting rings 28 are preferably arranged to be used for power supply, ground, and two control signals. In the present preferred embodiment, twisted-pair lead lines 34a preferably including shielding and core wires covered with an insulating layer are connected to the two electricity-collecting rings 28 preferably arranged to be used for high-frequency signals. Coated lead lines 34b are connected to the remaining electricity-collecting rings 28. The lead line group extending outwards from the shaft 16 is connected to a connector 38. Two signal lines 34a1 of the shielded lead lines 34a are twisted and connected to the connector 38. A shielded line 34a2 of the shielded lead lines 34a is connected to a ground lead line 34b within a receiver circuit of a monitoring camera to be connected to the connector 38. In the end portions of the shielded lead lines 34a, the signal lines 34a1 and the shielded line 34a2 are preferably secured to one another through, for example, a heat-shrinkable tube 36.
In this regard, when installing the electricity-collecting body 24 within the shaft 16, the rib plates 26c of the holder 26 are not directly fitted into the shaft 16. Instead, the holder 26 is fitted into the shaft 16 through the bush 32 which is fitted to the rib plates 26c. For that reason, the inner diameter of the shaft 16 is increased with respect to the size of the bush 32. Accordingly, the shielded lead lines 34a, which are relatively bulky, can be used without problems as the lead line group 34 inserted into the shaft 16. An insulating adhesive agent 40 is preferably filled into the shaft 16 to substantially fix the lead line group 34 within the shaft 16. Therefore, despite the relative movement of the fixed portion and the movable portion of the slip ring device, it is possible to prevent the occurrence of an electrical disconnection or a poor electrical connection which may otherwise be caused by the vibration of the lead line group 34.
A cover member 42 arranged to cover the electricity-collecting body 24 protruding from one end of the shaft 16 is provided at one end side of the tubular body 10 of the main case. The tubular body 10 and the cover member 42 preferably define the main case. A portion of the cover member 42 is defined by a circuit board 44 arranged orthogonal or substantially orthogonal to the plane extending across the axis of the electricity-collecting body 24. Pairs of the brushes 46 arranged to mate with the respective electricity-collecting rings 28 of the electricity-collecting body 24 are embedded in the circuit board 44 and are axially arranged along the arrangement direction of the electricity-collecting rings 28. More specifically, as shown in
In the circuit board 44, circuit patterns arranged to interconnect each pair of brushes 46 and to connect external connection terminals corresponding thereto are provided with respect to each pair of the brushes 46. As shown in
Where the slip ring device configured as described above is applied to, e.g., a monitoring camera, the tubular body 10 of the main case is preferably fixed to a base plate arranged to permit attachment of the monitoring camera by use of the attachment flange 10a with the axes of the tubular body 10 and the shaft 16 oriented in the vertical direction. The monitoring camera is attached to the yoke 18 in a hanging state. Thus, the monitoring camera is rotatably supported through the slip ring device to rotate with respect to the base plate. The connector of the lead line group 34 is connected to the monitoring camera, while the connector 50 of the lead line group 48 is connected to a processing unit arranged to control the monitoring camera and process the image information. The electric power and the control signals are supplied from the processing unit to the monitoring camera through the slip ring device. The image information is transmitted from the monitoring camera to the processing unit through the slip ring device.
The image signals from the monitoring camera are transmitted to the processing unit through the transmission route defined by the lead line group 34, the transmission route defined by the slip ring device in which the electricity-collecting rings 28 and the brushes 46 make sliding contact with each other, and the transmission route defined by the lead line group 48. In the case of high-speed high-frequency signals, such as, for example, image signals of a high-definition camera, the signals will be reflected in the joint portions of the respective transmission routes unless the impedances of the respective transmission routes are matched or substantially matched with one another. This leads to poor transmission and increased attenuation of the signals.
In the slip ring device where the electricity-collecting rings 28 and the brushes 46 make sliding contact with each other, the attenuation of the signals during the transmission of the high-frequency signals can be reduced or substantially reduced if the distance between the electricity-collecting rings 28 or the dimension of the brushes 46 is preferably smaller. In view of this, the distance between the electricity-collecting rings 28 or the dimension of the brushes is preferably kept as small as possible. Moreover, if the electricity-collecting body 24 is reduced in size and if the size of the shaft 16 is reduced in proportion thereto, it becomes difficult to insert the lead lines, particularly shielded lead lines, into the shaft 16. However, the use of the bush 32 in the electricity-collecting body 24 having a reduced size makes it possible to fit the electricity-collecting body 24 to the shaft 16 having a specified inner diameter. Accordingly, the lead line group 34 including the shielded lead lines 34a can be applied to the slip ring device.
In the preferred embodiment described above, the lead line group 34 including the shielded lead lines 34a is preferably included in the transmission route between the monitoring camera and the slip ring device. The lead line group 48 including the shielded lead lines 48a is included in the transmission route between the slip ring device and the external processing unit. The impedance of the slip ring device is matched with the impedances of these transmission routes. As a result, the attenuation of the high-speed high-frequency image signals of the monitoring camera in the respective transmission routes and the joint portions thereof is avoided or substantially alleviated. This makes it possible to transmit the image signals at an increased speed.
In the preferred embodiment described above, the electricity-collecting rings 28 for high-frequency signals are preferably arranged in the base portion of the electricity-collecting body 24. This is to shorten the lead line length as far as possible and to secure the signal transmission reliability.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-247053 | Nov 2010 | JP | national |
