Expansible chamber devices – With inspection window in expansible chamber wall portion – With lock
Reexamination Certificate
2001-02-26
2004-02-24
Lopez, F. Daniel (Department: 3745)
Expansible chamber devices
With inspection window in expansible chamber wall portion
With lock
C033S763000
Reexamination Certificate
active
06694861
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to position sensors, and more particularly, to linear position sensors for use on power cylinders.
BACKGROUND
Equipment implementing hydraulic cylinders for mechanical movement, such as excavators and other heavy construction equipment, depend upon operators to manually control the moveable elements of the equipment. The operator must manually move control levers to open and close hydraulic valves that direct pressurized fluid to hydraulic cylinders. For example, when the operator lifts a lift arm, the operator actually moves a lever associated with the lift arm causing a valve to release pressurized fluid to the lift arm cylinder. The use of levers to control hydraulic equipment depends upon manual dexterity and requires great skill. Improperly operated equipment poses a safety hazard, and operators have been known to damage overhead utility wires, underground wiring, water mains, and underground gas lines through faulty operation of excavators, bucket loaders or like equipment.
In addition to the safety hazards caused by improperly operated equipment, the machine's operating efficiency is also a function of the operator's skill. An inexperienced or unskilled operator typically fails to achieve the optimum performance levels of the equipment. For instance, the operator may not consistently apply the force necessary for peak performance due to a concern over striking a hazard. Efficiency is also compromised when the operator fails to drive a cylinder smoothly. The operator alternately overdrives or underdrives the cylinder, resulting in abrupt starts and stops of the moveable element and thereby derating system performance. As a result, the skill level necessary to properly and safely operate heavy equipment is typically imparted through long and costly training courses and apprenticeships.
There have been various attempts at implementing an automated control system for use on heavy equipment. One such system is disclosed in U.S. Pat. No. 4,288,196. The system described therein provides for a computer programmable system for setting the lowermost point of a backhoe bucket. In U.S. Pat. No. 4,945,221, a control system for an excavator is disclosed. The system attempts to control the position of the bucket cutting edge to a desired depth. Another position locating system for heavy equipment is disclosed in U.S. Pat. No. 5,404,661.
These systems and others like them share a common feature in that they implement a position sensor. Typically, these sensors are rotary potentiometers as, for instance, suggested in Murakmi, Kato and Ots,
Precision Angle Sensor Unit for Construction Machinery
, SAE Technical Paper Series 972782, 1997. This sensor relies upon a potentiometer which changes a voltage or current in relation to the position of a bucket or boom. Other types of sensors rely upon optical, conductive plastic, or metal-in-glass technologies.
It is a disadvantage of these sensors that they mount to the outside of the machinery, thereby exposing them to the environment. In the case of heavy equipment, this environment includes severe temperatures, excessive moisture, and air-borne particulate matter which may infect the sensor. In the case of optical, conductive plastic and metal-in-glass technologies, the sensors would rapidly degrade if used on construction equipment. Furthermore, some of these sensors use contacting components that are susceptible to wear, vibration and temperature. As a result, no sensor mountable to the outside of heavy equipment or relying upon contacting elements has gained widespread use in the industry.
There have been attempts to overcome the limitations of noncontacting sensors by using electromagnetic energy. For example, the system disclosed in U.S. Pat. No. 4,945,221 discloses using lasers for sensing problems. Others suggest using RF energy or the like to provide a feedback signal. These systems, however, have not replaced the less expensive potentiometers due to their complexity of use and their expense.
As the demands placed upon actuated machinery increases, so does the demand for a low cost, long-life sensor operable in a harsh environment. Despite the development of highly sophisticated control systems, computer processors and application specific software, the implementation of this technology in electrohydraulic equipment has been curtailed by the failure to provide a long-life, cost-effective precision sensor operable in harsh environments.
SUMMARY OF THE INVENTION
A sensor according to the principles of the invention provides a precision signal utilizing a non-contacting transducer. In an exemplary embodiment, the sensor mounts inside a hydraulic cylinder, away from the harsh environment, and provides a signal indicative of the position of the piston. The sensor provides a connector, attached between a cylinder piston and a converting element, for sensing the displacement of the piston. The converting element converts the cylinder displacement to a proportional displacement of a translating member. A precision transducer senses the displacement of the translating member and provides an electrical output signal proportional to the piston movement or to the piston's position.
In one exemplary sensor according of the principles of the invention, a flexible connector such as a cable is attached to the movable element (a piston). The converting element comprises a pick-up spool coupled to the other end of the connector and rotatable about an axis. The spool is under tension from a recoil mechanism, such as a spring, coupled to the spool. A translating member, which can be a lead screw, engages threads on the interior of the spool, and translates along an axis when the spool rotates. A transducer is disposed to sense a position or motion of the translating member, and provides an output signal proportional to, and therefore indicative of, the position (or motion) of the translating member. The transducer can be a linear variable differential transformer (LVDT), which is a non-contacting transducer. Of course, other transducers, including those using contacting components can be used.
As a further feature of a sensor according to the principles of the invention, and as a still further exemplary embodiment thereof, there is provided a construction of the sensor frame by the use of a plurality of stamped plates that are contained within the hydraulic cylinder, preferably about five of such stamped plates and which stamped plates facilitate the ease and therefore reduce the cost of the constructing of an exemplary sensor, that is, with the use of a plurality of stamped plates, a frame for the sensor can be readily formed by the stamping process and which eliminates the need for specially complex machined blocks to thus reduce the cost of such construction. Also, with such embodiment, in addition to the considerable cost savings, there is a greater flexibility in the production of sensor frames of differing sizes by merely adapting the stamping techniques to produce the stamped plates of the appropriate dimensions for the particular desired size of sensor. As such, with relatively minimal tooling changes, the size of the various sensor frames can be changed, modified and adapted to accommodate a wide variety of dimensioned sensors to be located within the hydraulic cylinder.
As a still further exemplary embodiment, there is provided an improved mounting means whereby the sensor can be physically mounted within the hydraulic cylinder by utilizing the standard hydraulic threaded fluid ports that are normally found on such hydraulic cylinders. In this improved mounting means, use is made of the pair of standard hydraulic fluid ports that are located about 180 degrees apart on the periphery of the hydraulic cylinders. Flexible end caps comprised of a flexible material such as urethane, are positioned about the sensor and juxtaposed and in alignment with each of the fluid ports of the hydraulic cylinder. Two port inserts are then threaded, respectively into each of the standard fluid p
Control Products Inc.
Gibbons Del Deo Dolan Griffinger & Vecchione
Lopez F. Daniel
LandOfFree
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