Non-contacting sensors

Details Non-contacting sensors Non-contacting sensors

1999-02-08

2003-12-30

Lefkowitz, Edward (Department: 2855)

Measuring and testing

Dynamometers

Responsive to force

C324S207150

Reexamination Certificate

active

06668668

ABSTRACT:

FIELD OF INVENTION
This invention relates in general to a method and device for determining the forces applied to a support member or cable. In particular, the deflection of the support may be measured to determine the force input to a support member or a payload suspended by the support member. Other embodiments of the invention relate to a method and device for measuring forces applied along a single axis as well as a method and device for determining the orientation of a surface or object.
BACKGROUND OF THE INVENTION
Motorized gantry cranes as well as non-motorized overhead rail systems may be used to assist a human operator in moving bulky or heavy payloads. In either case, a powered hoist is most commonly used to lift the payload. For large loads supported by a gantry crane, a motor-driven trolley and bridge rail transport the hoist in accordance with the operator's commands issued through a control box. For smaller loads supported by an overhead rail system the operator may push on the payload directly, causing the free-rolling trolley and bridge rail to follow along passively.
An intuitive interface to the gantry crane would allow better dexterity than is afforded by a control box. An intuitive interface to the overhead rail system would allow the addition of motors without reducing the operator's dexterity. Thus, an appropriate interface would allow gantry cranes the benefit of the operator's dexterity and overhead rail systems the benefit of powered motion.
In either case the powered motion of the trolley and bridge rail must reflect the operator's intent, which is most naturally expressed by pushing directly on the payload. If the payload is suspended by a support means or cable, the degree and direction of its deflection may be used to indicate the force applied to the payload by the operator.
A number of different techniques have been practiced to measure the position or movement of a support means or cable suspending a payload. Typically, mechanical means of detecting the position of the support have been used, such as a moveable wiper arm running against a potentiometer. The resistance varies as the moveable wiper arm moves along the length of the potentiometer.
U.S. Pat. No. 3,982,733 to Orme entitled “Gimbaled Sheave With Cable Angle Sensors” describes a system for maintaining the position of a helicopter or waterborne platform over a underwater array suspended from a cable by measuring the angle of the cable. The angle of the cable is measured using a conventional mechanical means, a rotary transformer encoder. The patent describes a design of a gimbaled sheave from which the cable pays out that allows the angle of the sheave to be measured by the rotary transformer encoder to determine the angle of the cable.
U.S. Pat. No. 5,350,075 to Kahlmann entitled “Arrangement For Controlling The Direction And Movement Of A Load Hoist Trolley” also describes a mechanical means of measuring the movement of a cable. The movement of the cable is used to determine the force manually applied to a payload suspended from a cable. The force applied by an operator to the payload produces a displacement of the payload and the suspending cable.
Slightly below the hoist, the cable passes through a guide that moves laterally as the cable moves with the movement of the payload. The lateral motion of the guide is measured and gives an indication of the force applied by the operator.
A mechanical device coming in contact with the movable support, however, can constrain and impede the motion of the support and may be easily damaged by a sudden violent or uncontrolled movement of the support. In an industrial application, even a relatively small and controlled movement of a heavy payload can be translated and magnified to a sudden and violent movement of its supporting means. To provide a device capable of withstanding the rigors of such potential shocks and impacts without sustaining damage, an attempt can be made to construct the device of sufficient structure rugged enough to withstand such shocks. Such a durable device of increased ruggedness, however, may be heavy, expensive to build, and still constrain the movement of the support. Thus, to efficiently and reliably detect the motion of the support, a mechanism that does not contact the support is desired.
To this end, a number of optical and electrical means of detecting the position of a support without physically contacting the support have been suggested.
U.S. Pat. No. 5,785,191 to Feddema entitled “Operator Control Systems And Methods For Swing-Free Gantry-Style Cranes” describes techniques for eliminating the unwanted swing of a payload suspended from a crane. Gantry-style cranes are usually moved by operating left/right & forward/back push buttons to start and stop the crane. The sudden stops and starts of the crane cause the suspended payload to swing. The patent suggests a non-contact cable angle sensor using a capacitance measurement but does not disclose the suggested cable angle sensor.
U.S. Pat. No. 4,464,087 to Schumann entitled “Inductively Coupled Position Detection System” shows a non-contacting technique for determining the position of a handheld joystick moveable member relative to two or three orthogonal axes. The disclosed system shows an inductively coupled position sensing device having a drive coil affixed to the moveable member of interest and pickup coils which are located to define a pair of intersecting stationary axes, i.e. an X-Y coordinate system with four quadrants. One of the pickup coils is located in each of the quadrants. The pickup coils are arranged and interconnected such that the mathematical sum of the induced voltages will be of a magnitude and polarity indicative of the position of the moveable member. The disclosed device is configured for a joystick application that may be suitable for a force-sensing handle. It is still, however, not suitable for an overhead rail system where the payload is free to rotate and swivel without providing directional information.
Thus, it would be desirable to provide a system capable of improving the detection and measurement of force applied to a suspended payload.
In addition to moving a payload in the lateral direction, there is also a need to control the load in the up-down direction or Z-axis direction. A hoist for lifting heavy objects is typically controlled by a control box having up/down push buttons. To cause the hoist to raise the payload, a button corresponding to raising the payload up is pushed and released.
To lower the payload, a second button corresponding to lowering the payload is pushed and released. Raising and lowering the load through the actuation and release of the control push buttons require the operator to carefully watch the load and time his actuation and release of the push buttons. Thus, it is desirable to provide a more intuitive and direct method of operating the hoist to raise and lower the load.
When the operator's force in a lateral direction causes the bridge rail of a gantry crane to traverse along its long rails, it is necessary to control the motion of the bridge rail such that it remains perpendicular to the long rails. This may be done by sensing any deviation from perpendicularity and correcting the deviation. The sensing of the skew angle of the bridge rail is subject to similar requirements of ruggedness as those involved in the sensing of lateral movement of the cable, and the sensing of axial forces along the cable. A non-contact sensor is desirable for this purpose.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the invention, problems associated with measuring the deflection of a support member or suspended cable are addressed. The illustrative embodiment of the invention can be used, for example, to measure the magnitude and direction of forces applied to a payload attached to the support member. From the measured deflection of the support member, the forces applied to a payload can be determined. The illustrative embodiment can be used with a gantry crane

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