Robotically drivable interface mechanism

Details Robotically drivable interface mechanism Robotically drivable interface mechanism

1999-07-19

2001-09-18

Cherry, Johnny D. (Department: 3652)

Handling: hand and hoist-line implements

Grapple

C244S164000, C414S729000, C901S030000

Reexamination Certificate

active

06290275

ABSTRACT:

The present invention relates to a robotically drivable interface mechanism to couple a payload to a device and to couple a robot arm to the payload, enabling handling of the payload by means of the robot arm.
More specifically, the invention relates to a robotically drivable interface mechanism handling payloads on devices, such as platforms, in space applications also known as on-orbit servicing of payloads. The handling of payloads may include the uncoupling of a payload from the device, the movement of the payload from one place on a device to another, the recoupling of the payload to the device, or manipulation of payload subsystems, e.g. samples, optical units or dust capture panels.
Such a robotically drivable interface is known, for example, from “End effector for on-orbit servicing of payloads” by B. C. Braam and R. Ramaker, Proceedings Sixth European Space Mechanics & Tribology Symposium, Zürich, Switzerland, Oct. 4-6 1995. This article describes various aspects of the handling of payloads on a space platform by a robot arm, and more specifically the handling of payloads on the External Viewing Platform with a robot arm provided with an end effector to couple the robot arm to a payload.
The end effector attached to the end of the robot arm is manipulated by the robot arm, until it is within the required guiding range. Then, with the help of guiding aids, the end effector is guided to a ‘connection ready’ position and, ultimately, the end effector couples to the payload and the required handling of the payload can start. In the end effector design according to this article, three distinct functions are envisaged, i.e. the guiding, positioning and latching function.
The guiding and positioning function is performed by a so-called kinematic clamp, consisting of three V-grooves on the end effector and three semispheres on the payload to be manipulated. The three semispheres provide six contact points (two in each V-groove), thereby providing fixture of the position of the end effector with respect to the payload in three translational and three rotational axes. A pretension force is necessary to maintain the realized position. This pretension force is provided by a controllable electromagnet in the end effector and a permanent magnet positioned on the payload. To ensure safe operation, the controllable electromagnet is arranged not to exert a force on the permanent magnet when powered and to exert a force on the permanent magnet when not powered.
The known end effector is further provided with latching means, arranged as hooks to couple the end effector with a grapple fixture on the payload. These hooks are provided with a safety mechanism to ensure the coupling stays intact under all circumstances.
For payload servicing in space applications, a number of requirements exist regarding the interfaces between the platform and the payload, respectively between the payload and the end effector of a robot arm, enabling the exchange of payloads and payload subsystems, deployment of equipment and operation of instruments. As the payload is usually attached to the platform during launch, the interface between them has to withstand the forces (caused by acceleration and vibration) during launch. Studies have indicated that two combined aspects have a main influence on the design of the necessary interfaces, i.e. the launch loads and the end effector capabilities.
In most cases, the interface between the platform and the payload is also in place during launch, therefore, this interface has to be able to withstand high launch loads (>3000 N), necessitating high holding forces on the interface mechanism. To be able to exert these holding forces, the end effector would have to be provided with gripping tools that are either very complex or have a high volume and mass. For space applications, it is necessary that all elements are as light as possible, to save on material and launch costs. Finally, also requirements can exist with regard to lifetime of components and assemblies, as no or little possibilities exist to repair these items in space.
Therefore, it is the object of the present invention to provide a robotically drivable interface mechanism being attachable to a payload for coupling the payload to a device and being attachable to an end effector attached to the end of a robot arm for coupling the robot arm with the payload thereby enabling the robot arm to handle the payload, which has a simple design, low weight and volume and a long lifetime.
This object is achieved by the robotically drivable interface mechanism according to a first embodiment. By providing the first coupling means on the interface mechanism as at least one roller cooperating with the second coupling means formed by at least one slot in the device, an effective coupling mechanism results that is compact and able to withstand high launch loads. The roller may be a rotatable wheel mounted in a bearing, or a fixed round body able to move in the slot in the device with low friction. Preferably, the first roller is spring mounted, providing a pretensioned coupling between the interface mechanism and the device. Because of the compactness, the interface mechanism is easy to assemble, and can weigh less while maintaining the requirements with respect to launch loads, etc.
In a second aspect, the present invention relates to an interface mechanism according to another embodiment.
This embodiment of the interface mechanism is able to withstand the high launch loads that occur between the device and the payload. The interface mechanism according to the present invention is equipped with a screw spindle and nut assembly to move the roller frame from a first position in rest to a second position. This has the advantage that less force is needed to couple the interface mechanism to the device (±1 N/m
2
) compared to earlier coupling mechanisms, often requiring a force of 20-25 N/M
2
. Furthermore, this embodiment also provides an effective latch function for the first and second coupling means, as a relatively large force is needed to move the roller frame coupled to the screw spindle by the nut.
In a preferred embodiment of the present invention, an interface mechanism is provided according to another embodiment. The second and third rollers allow a reliable movement of the roller frame with respect to the roller runway for allowing the first roller to engage an inner surface of associated second coupling means on the device to couple firmly with the device.
In a third aspect, the present invention relates to an interface mechanism according to a further embodiment. This embodiment shows the same advantages as the embodiment mentioned above. In addition, the fact that the pretension between the interface mechanism and the device is slowly built up by the sloped surface has the advantage, that the first guidance means and associated second guidance means don't have to be precisely aligned, as the pretension force will tend to draw them into the precise position.
A further preferred embodiment of the interface mechanism is also described. By providing at least one spring mechanism in the assembly of roller frame and roller runway, a pretension force is exerted between the interface mechanism and the device when the roller frame is moved from the first position to the second position. This pretension force will allow the combination of interface mechanism and device to withstand higher loads, e.g. during launch. The spring may be provided in the mounting of the first roller to the roller frame, or alternatively by mounting the roller runway to the interface mechanism by means of a spring blade.
A further aspect of the present invention relates to a system comprising an interface mechanism according to the embodiments of the invention and a device being arranged for coupling to the interface mechanism. The first and second guidance means allow the interface mechanism and device to be guided to a well defined position with respect to each other.
A comparable arrangement can be defined for a system comprising

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