MEANS FOR ADJUSTING THE EXTREME POINTS OF THE MOVEMENT OF THE PISTON IN A WORKING CYLINDER

Abstract: The means comprises a variable resistance (R1), two set resistances and two comparing members which compare the variable resistance to these set resistances and give a control signal to the control valve of the working cylinder when the value of the variable resistance (R1) is the same as the value of either one of the set resistances. The variable resistance (R1) is arranged adjacent to the path of movement of the piston in the working cylinder and comprises a resistance element (4) and a strip of magnetic material (5) which is located on the opposite side of the resistance element (4) relative to the piston and which has laterally projecting flexible transverse strips (6). A part (3) of the piston is formed as a magnet whereby, as the piston moves along the adjusting resistance, said transverse strips (6) are successively bent into engagement with the resistance element (4) and, accordingly, the value of the resistance changes as the piston moves therealong.

Description: Means for adjusting the extreme points of the movement of the piston in a working cylinder Specific positions of a moving member can be deter- mined by utilizing a principle coupling according to figure 1. It comprises a variable resistance R1 and two comparing members 1 and 2 which compare the resistance R1 with two set resistances R2 and R3 and give an indication when the value of the resistance R1 is the same as the value of the resistance R2 and the resistance R3, respectively. Thus, by making the moving terminal of the resistance R1 to follow the movement of the body under observation it is possible to obtain an indication when the body under observation reaches, for example, the positions a and b marked out in the figure 1 , in which positions the value of the resistance R1 is the same as the value of the resistance R2 and the resistance R3, respectively. In hydraulic and pneumatic cylinders it is often desirable to adjust the stroke length and the movement of the piston in general between two extreme points. The object of this invention is to provide a new means which, based on the above-mentioned principle, offers a simple means of adjusting the movement of the piston in a cylin- der. Thus, the invention relates to a means for adjusting the extreme points of the movement of the piston in a working cylinder which comprises a variable resistance, and two comparing members for comparing the variable resistance with two set resistances. The means is characterized in that the variable resistance is arranged adjacent to the path of movement of the piston of the working cylinder and comprises a resis¬ tance element parallel to the path of movement and a strip of conductive, magnetic material which is located on the opposite side of the resistance element relative to the piston and has laterally projecting flexible transverse strips, and in that a part of the piston is formed as a magnet whereby, as the piston moves along the variable resistance, said transverse strips are, under the influen- ce of the magnet, successively bent into engagement with the resistance element and, accordingly, the value of the resistance is changed as the piston moves therelong. In the following, the invention will be described with reference to the accompanying drawing in which figure 1 shows, as mentioned above, a general principle coupling to which the invention has been applied and figure 2 shows schematically one embodiment of a variable resistance used in the invention. The comparing members 1 and 2 compare the value of a resistance R1 with set resistances R2 and R3. The comparing member 1 gives an indication when the resistance R1 is equal to the resistance R2 and the comparing member 2, respectively, gives an indication when the resistance R1 is equal to the resistance R3. These points have in the resistance R1 been designated a and b. According to the invention, the above-mentioned principle, known per se, is applied to adjusting the extreme points of the movement of the piston in a working cylinder in the following manner. The resistance R1 is arranged adjacent to the path of movement of the piston parallel therewith. A part of the piston or piston rod is magnetic, in the figure 2 this magnetic part is drawn very schematically and denoted with reference numeral 3. The resistance R1 comprises a resistance element 4 and a strip 5 which is arranged close to it and provided with transverse strips or tongues 6. The strip 5 and the tongues 6 are of electrically con¬ ductive magnetic materila and the strip 5 is connected to plus potential while the resistance element 4 is connected to earth. The magnet 3 and the flexible tongues 6 are located on opposite sides of the resistance element 4, and when the magnet moves along the resistance element 4 and pulls a tongue 6 at each particular moment located at the magnet 3 in engagement with the resistance element 4 and, as the magnet has advanced, the tongue due to its elasticity again returns away from the resistance element. Thus, the resistance to be measured from plus poten¬ tial to earth will change as the movement of the piston advances, and when the resistance is equal to R2 and R3, the comparing member 1 and 2, respectively, give a control signal to the control valve of the cylinder in a manner known per se. By changing the values of the resistances R2 and R3 it is thus in a simple manner possible to vary the extreme points a and b of the movement of the piston in a desired manner. The drawing is only intended to illustrate the idea of the invention. In practice, for example, the tongues 6 can be considerably more closely spaced and an indivi¬ dual tongue can be narrower so that several tongues, at a time, will be bent into engagement with the resistance element 4, whereby a precise adjustment is obtained. In principle, the resistance element 4 can be a conventional wire resistance which preferably is shaped flat so that the magnet 3 will be able to act on the tongues 6 from a close distance. The resistance element 4 can also be a continuous rod or strip made of a suitable material, in which case the resistance of the material must be so high that it changes as the point of contact between it and the tongues 6 is moving along the resistance element.

Claims: Claims: 1. A means for adjusting the extreme points of the movement of the piston in a working cylinder which co - prises a variable resistance (R1), and two comparing members (1 and 2) for comparing the variable resistance with two set resistances (R2 and R3), c h a r a c t e ¬ r i z e d in that the variable resistance (R1) is arranged adjacent to the path of movement of the piston (3) of the working cylinder and comprises a resistance element (4) parallel to the path of movement and a strip (5) of conductive, magnetic material which is located on the opposite side of the resistance ' element relative to the piston (3) and which has laterally projecting flexible transverse strips (6), and in that a part of the piston (3) is formed as a magnet whereby, as the piston (3) moves along the adjusting resistance, said transverse strips (6) are, under the influence of the magnet, successively bent into engagement with the resistance element (4) and, accordingly, the value of the resistance (4) changes as the piston (3) moves therealong. 2. A means as claimed in claim 1, c h a r a c t e ¬ r i z e d in that the resistance element (4) is formed flat in order to bring the magnet (3) close to the flexible transverse strips (6) of magnetic material.

Inventors: IIVARINEN A
Applicants: IIVARINEN A
Application year: 1981
Main classification: G05D3
IPC codes: G01D5