1. Field of the Invention
The present invention relates generally to connectors which can be mated and unmated in very harsh environments, such as underwater, and is particularly concerned with a robotically mateable, rotary joint electrical connector usable in such environments.
2. Related Art
There are many known electrical rotary joint connectors which function in dry environments, but not many that are suitable for harsh or underwater environments. Harsh environment rotary joint connectors are currently in use only for limited applications, such as down-hole drill strings, but they are not intended for general use, or for mating while completely submerged in a hostile environment.
Modern underwater systems, particularly sea floor systems, are generally of modular architecture with individual modules added and removed in-situ, and these modules are typically electrically interconnected by various jumper cables which have underwater mateable and demateable connectors on one or both ends. The connectors consist of two mating halves or units, specifically a plug unit and a receptacle unit. When these connector units are brought together in the mating process, the following relative alignment aspects must be controlled: axial offset (along the mating axis), axial tilt (of the mating axes), and rotation about the mating axis. The last of these, which requires rotational keying, is the most difficult to control.
All jumper cables have some resistance to torque, so that if one end is fixed, or substantially fixed due to great length, it is often very difficult to rotationally orient the free end into mating position, particularly if using the robotic manipulator of robot or robotic vehicle, such as an underwater vehicle or remotely operated vehicle (ROV). The problem is increased for very short jumper cables which cannot support much twist. Even in conditions where there is little cable torque, the problem of finding the mating key/key slot position increases the difficulty of connecting the jumpers. It would therefore be advantageous to provide a system where no keying of the mating connector portions or units is required, and which avoids the problem of twisting of the jumper cable when the connector on the cable's free end is rotated, as happens due to underwater vehicle maneuvering.
Most current underwater connectors designed for mating while completely submerged need to have the plug and receptacle parts keyed into rotational alignment for mating. Many of the connectors used for the oil and gas industry's subsea operations are connected and disconnected remotely, either by being mounted to large, opposed plates (stab plates) that come together during the mating process to join arrays of connectors, hydraulic couplers, and the like, or by robotic manipulators such as manipulators of remotely operated vehicles (ROV's). Mating remotely is made more difficult and expensive by the requirement to control the rotational alignment of the individual components to be mated.
In the early 1980's two-contact fluid-filled electrical connectors that required no rotational alignment were made commercially available. One example of such a connector is described in U.S. Pat. No. 4,606,603 of Cairns. These connectors did solve the rotational alignment problem, but one problem with such connectors was that two contacts were not enough to satisfy the needs of most operations. Another problem was that the receptacle's circular end-opening, which had to be pinched tightly closed before and after mating, had to be stretched several hundred percent to receive the plug's pin. If mated for a long time, particularly at low ocean temperatures, the opening did not close upon de-mating, and the connector subsequently failed.
In the late 1980's, multiple pin, fluid-filled connectors were once again introduced. They have all the required barriers, are robust, and exceptionally reliable. One such connector is the subject of U.S. Pat. No. 4,948,377 of Cairns. These connectors are manufactured by Teledyne ODI. They replaced the two-contact, single pin fluid-filled connectors described above as the high-reliability standard for the offshore industry. These connectors still have the rotational alignment problem, however, which somewhat limits their use, and requires special keying provisions for rotational alignment.
In the early 1990's a keyless, coaxial, oil-filled, wet-mateable connector was introduced that required no rotational alignment. This connector is described in U.S. Pat. No. 5,171,158 of Cairns (hereinafter '158 patent). It consisted of multiple ring-like contacts spaced along a constant diameter portion of the plug pin. The receptacle had corresponding ring-like contacts spaced along a rubber bore to receive the plug contacts. The overall layout of the contacts was very similar to the first type of connector described above. The main differences were that the connector of the '158 patent housed the receptacle contacts in a pressure-balanced, fluid-filled chamber; and, when mated, the individual pin/socket pairs were separated from each other by a single rubber seal. Unlike the coaxial connector of U.S. Pat. No. 4,606,603 (hereinafter '603 patent), the anterior sealed opening through which the plug's probe passed when entering the receptacle's chamber was occupied by a spring loaded piston before and after mating. That removed the necessity of the sealed opening to be pinched closed to a zero diameter as in the '603 patent.
The connector shown in the '158 patent was reasonably successful technically and quickly gained a dedicated customer base, but it was discontinued after being on the market for just a couple of years. It proved to be too expensive and difficult to manufacture. It also still had the problem of cross-connection during mating and de-mating as the plug's contacts wiped across receptacle contacts which were not their intended counterparts.
Underwater and other harsh environment connectors today typically require rotational alignment or keying for connection in a harsh environment, which makes robotic mating and demating difficult to accomplish, and also often results in torque or twisting of the flying lead jumper cables.