Education and demonstration – Vehicle operator instruction or testing – Flight vehicle
Reexamination Certificate
2000-03-17
2002-10-22
Banks, Derris H. (Department: 3712)
Education and demonstration
Vehicle operator instruction or testing
Flight vehicle
C434S057000, C434S058000
Reexamination Certificate
active
06468082
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to motion-imparting apparatus of a type capable of imparting motion to a load for the purpose of positioning it or for the purpose of controlling or modifying its motion. The present invention finds applications in a wide range of devices including, for example, positioning devices of manufacturing machinery. Generally, such machinery does not require the device to do mechanical work on a material, (e.g. to cut it or to deform it) but rather to control the position of a mass which moves on a low-friction bearing system. Such machines are often required to carry out a precisely-defined positioning action at a high repetition rate and with a negligible error incidence. In such a machine the use of an electromagnetic ram has advantages over other types of actuator in that it is intrinsically simple in its construction, it has a zero backlash and it has a zero control transport lag. These valuable properties allow an electromagnetic actuator to produce rapid motion with extreme precision and reliability. It is possible to apply forces of more than 20 Tonnes to be applied at several meters per second with a positioning accuracy of a few microns.
Such apparatus is also used, for example, in simulators for training or entertainment. Typically in such use a platform is moved in relation to a static structure in order to create sensations of continuous movement for human occupants of a capsule affixed to the moving platform. Such mechanisms are also used in the testing of suspension systems and stabilising apparatus, whereby the motion platform is used to create calibrated disturbance accelerations, against which the operation of the stabilising mechanism requires to be tested. The moving platform of motion-imparting apparatus is normally actuated by an array of actuator units or “rams” which may be driven by hydraulic fluid or gas under pressure, or by ram-like devices which are electrically operated by means of a ball-nut and screw mechanism. More recently, apparatus has been designed to use a geared-down crank fitted to rotary motor, or to employ direct electromagnetic interaction between a moving piston-shaped armature and a cylindrical stator. In the case of the latter electrical and electromagnetic machines, there is a requirement for the motion-imparting apparatus to be supported against the gravitational forces acting upon the capsule and its occupants by some means. This is important because energy would otherwise be continuously consumed within the electrical machine in order to create the thrust required to counteract the constant gravitational force acting upon the capsule. This would soon cause the motors to overheat. This effect is also encountered in other applications.
One attempt to solve this problem is described in International Patent Application published under WO93/01577. This document describes a technique that carries the load of the motion platform on a counterbalancing mechanism having a low effective spring rate. As a particular example a cranked gas spring system is described therein. Experience with mechanisms that have been constructed in accordance with the disclosure of WO93/01577 has shown that the concept of counterbalancing described therein does not provide optimal support for an electromagnetic motion base. The present invention, in one concept, is based on the realisation that a controlled spring (or a set of controlled springs) with a significant spring rate is required for optimum support.
Hitherto, a number of designs of electromagnetic actuator, or linear motor, have been produced. Various configurations of previous machines have been described in documents such as WO93/01646, which discloses an electromagnetic device arranged to operate with cylindrical symmetry as a piston-in-cylinder machine. The principal advantage of that form of construction is that the strong attractive forces between the permanent magnets within the machine and the magnetic materials that surround them are balanced about a central axis, so that the bearings of the machine do not need to withstand any large magnetic forces.
A further advantage of the cylindrical construction is that the magnetic fields of the machine are contained within the outer steel case of the actuator or ram and that they can be arranged to intersect the electrical coils of the machine with a high degree of efficiency.
Yet another advantage of the cylindrical construction is that the armature of the ram may carry a sliding seal between it and the inside surface of the stator of the ram so as to form the piston of a fluid actuator device. This is beneficial when there is a requirement to produce fast-acting electromagnetic forces that are superimposed upon or intermittent with steady or slowly-changing forces. The latter types of force are better produced by means of a fluid actuator. The electromagnetic elements would otherwise be required to consume electrical power continuously if they were themselves to provide the static or slowly-changing force.
Further, the cylindrical, piston-in-cylinder construction is appropriate to the application of the ram in of many industrial control applications where hydraulic or pneumatic rams are now employed. This is because the magnetic fields of the ram are wholly-contained within the cylindrical casing, so that the ram is tolerant to the presence of swarf or other magnetic dust that is a problem to other types of electromagnetic linear actuator.
The present invention seeks to provide a structure in which the cylindrical stator cavity of an electromagnetic actuator is divided into two parts by a seal on the piston/armature element, and includes means by which the armature assembly may also act as the force-producing element of a fluid pressure control system for example as part of a gas spring.
It is to be noted that WO93/01646 and its associated co-pending application WO93/01577 describe a ram construction for application to motion base machines in which the gas spring property of the ram is conceived to act in one direction only, so as to support the weight, that is to resist a gravitational force. For this purpose WO93/01646 describes the construction of a passage for fluid flow connection of only one part of the ram cylinder (namely the underside of the piston) to a pressurised fluid reservoir forming part of a gas spring. Both WO93/01646 and WO93/01577 describe that the upper part of the piston is allowed to vent to atmospheric pressure, directly or via an exhaust reservoir.
It is desirable to have. a more efficient method of controlling the motion of an actuator simulator mechanism than that of WO93/01577, using a combination of air pressure and electromagnetic forces in which the individual forces and force gradients of the gas springs are optimised in relation to the dimensions of the load so that the energy consumed by the mechanism is at a minimum. For this purpose the gas springs acting beneath the piston of each ram should not be designed solely for the support of the load as in WO93/01577 but rather should function as temporary reservoirs in which the potential energy resulting from the electromagnetic action of the rams is stored and from which it can be recycled a short time later. This energy recycling technique results in an economy of power consumption which improves the performance and reduces the costs of construction and operation of an electromagnetic actuator.
OBJECTS AND SUMMARY OF THE INVENTION
In one aspect, therefore, the present invention seeks to provide a motion-imparting system in which a continuous load component is supported in an especially effective manner. It is a feature of embodiments of this invention that as applied to so-called motion-bases they have a form which is easily adapted to support a variety of capsule shapes, which is physically stable and robust, which has an enhanced ability to produce large angles of pitch and roll motion and which is easily accessible for inspection and service.
According to one aspect of the present invention there is provided app
Advanced Motion Technologies LLC
Banks Derris H.
Darby & Darby
Fernstrom Kurt
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