Motors: expansible chamber type – Working member position feedback to motive fluid control – Electrical input and feedback signal means
Patent
1988-07-08
1990-01-30
Look, Edward K.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Electrical input and feedback signal means
91393, 91461, 414699, F15B 1316
Patent
active
048965820
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and device for reducing the piston speed as the piston approaches end positions in a piston and cylinder assembly in an excavating machine, for example.
DESCRIPTION OF THE BACKGROUND ART
An excavating machine usually comprises a number of pressure medium-operated cylinders (pneumatic/hydraulic cylinders). Thus, an excavating machine has hydraulic cylinders for, inter alia, the boom and shovel stem movements of the excavating unit. If the cylinder end positions are not dampened, jolts occur which subject the cylinders, the boom and the shovel stem to sizable loads by which the working life of these parts is reduced materially, simultaneously as the actual excavating movement is adversely affected. In some cases, however, these jolts are put to good use, for example for emptying the shovel of an excavating machine.
Many different devices are known in the art for reducing the rate of motion of a piston. The most common device is a transducer which mechanically senses the position of the piston in the end region and activates a means for throttling the supply of pressure medium. However, devices of this type are difficult to mount and are not fully reliable. It is also known to design the piston and/or the cylinder ends in a specific manner, for instance by mounting on the piston a pin which projects into the mouth of the pressure medium drainage channel to throttle the flow. Also solutions of this type are open to objections. It is obvious that a reduced piston movement is unnecessary when the piston moves away from the adjacent cylinder end.
Prior art patented devices are described and shown in the two French patent Nos. 2,125,982 and 2,178,549 and in the European patent No. 0,022,105. According to these patents, the position of the piston is recorded continuously, i.e. also during the entire retardation period of the piston. According to French patent No. 2,125,982, the retardation of the piston movement at the end position is always initiated in the same cylinder position, irrespective of the piston speed, so that the speed reduction starts at an uncalled-for early moment at low speeds. In addition, the electrical circuit employed causes the retardation to be the same in both end positions.
According to French patent No. 2,178,549, on the other hand, the start of retardation is postponed at lower piston speeds. However, the actual speed reduction occurs regardless of how far the piston has travelled from the end position. Also in this case, the retardation is the same in both end positions. Different retardations for the two end positions would be preferable because the pressure-actuated piston area frequently is larger at one piston end than at the other so that different speeds occur. The above-mentioned shortcomings are eliminated by means of the device according to European patent No. 0,022,105 in which, however, a continuous recording of the piston position is a prerequisite. Besides, this device cannot be used in an excavating machine where end position jolts are an object to be desired.
SUMMARY OF THE INVENTION
It is the object of the present invention to eliminate the above-mentioned shortcomings, and this object is achieved by means of a method comprising the steps of generating a position signal when the piston passes a predetermined position adjacent the ends of the cylinder; supplying the position signal to a signal processing system; supplying the position signal, a reference signal and a control signal to a delay unit; comparing the control level signal to the reference signal; generating a comparison signal after a delay time period based on the comparing; applying the comparison signal and the control level signal to a braking unit; processing the comparison signal and control level signal by the braking unit to generate an output signal; applying the output signal and a signal indicating direction of piston travel to a setting system; and controlling supply of piston medium to the piston and cylinder by the setting system to thereby reduce th
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patent: 4733600 (1988-03-01), Masano
Bruhn Ingvar
Tordenmalm Lars O.
Akermans Verkstad AB
Look Edward K.
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