PROPORTIONAL MECHANO-ELECTRONIC ACTUATOR MEANS

Abstract: The invention relates to a proportional mechanical actuator for a device linearly controllable by a pressure fluid, the actuator being intended to be connected between a pressure source (P) and the device (60) to be controlled, comprising a proportional magnet (1); a pilot control spindle (3) arranged to be movable in a pilot control body (5) by the proportional magnet (1) for opening and closing different pressure fluid conduits (A, B, P, T); a positioner (11) for the device (60), the positioner (11) being linearly controllable in two directions by the pilot control spindle (3) so that the spindle (3) tends to keep the positioner (11) at each particular moment in a predetermined position corresonding to a control signal supplied by an electric control unit (70) of the actuator so as to linearly control the device (60) through a control spindle (14) or other similar external coupling device of the actuator. A position sensor (13) electrically sensing the position of the positioner (11) is provided in a substantially cylindrical means (12) defining a space where the positioner (11) moves, the position sensor comprising a winding fitted around the means (12).

Description: Proportional mechano-electronic actuator means The invention relates to a proportional mechano-electronic actuator means for a device linearly controllable by a pressure fluid, the actuator means being intended to be connected between a pressure source and the device to be controlled, comprising a proportional magnet; a pilot control spindle arranged to be movable in a pilot control body by means of a proportional magnet for opening and closing different pressure fluid conduits; a positioner means for the device to be controlled, the positioner means being linearly controllable in two directions by means of the pilot control spindle so that the pilot control spindle tends to keep the positioner means at each particular moment in a pre¬ determined position corresponding to a control signal supplied by an electric control unit of the actuator means so as to linearly control the device to be controlled through a control spindle or other similar external coupling device of the actuator means. A device of this type is known e.g. from EP Patent Specification 0 151 174, in which a pilot control spindle and a positioner are in mechanical contact with each other, the determination of the position of the positioner being inaccurate and its response relatively slow. The object of the present invention is to eliminate the drawbacks of the prior art. This object is achieved by means of an actuator means according to the invention, which is characterized in that a position sensor electrically sensing the position of the positioner means is provided in a substantially cylindrical means defining a space where the posi- tioner means moves, the position sensor comprising a winding fitted around said means. The valve according to the invention is connectable to any valve, and it is especially well suited for the control of a mobile directional valve, for instance. In the following the invention will be described in greater detail with reference to the attached drawings, in which Figures la, 2a, 3a and 4a show side views of the actuator means according to the invention in a partial section in different operating positions, the actuator ' means of Figure 4a deviating slightly from the actuator means of Figures la, 2a and 3a with respect to the arrangement of the position sensor; and Figures lb, 2b, 3b and 4b show pressure line coverage patterns associated with the operating posi¬ tions shown in the above-mentioned figures. Figures la, 2b and 3a show a proportional mechano-electronic actuator means comprising a pro¬ portional magnet 1, a pilot control unit 30, a posi¬ tioner unit 40, a feed and return part 50 for pres¬ sure fluid, and an electronic unit 70, which are all connected fixedly together into a compact actuator means aggregate. The pilot control unit 30 comprises a body 5 provided with a cylindrical boring 6 in which a ver¬ tically movable pilot control spindle 3 is posi¬ tioned. The spindle 3 comprises an upper annular shoulder 7, a lower annular shoulder 8 and an annular conduit 9 positioned therebetween. A spring 4 is pro¬ vided in the boring 6 below the pilot control spindle 3, a spindle 2 of the proportional magnet 1 moving the pilot control spindle 3 against the tension of the spring 4. The body 5 further comprises a pressure fluid conduit P and a pressure fluid return conduit T communicating with the pressure fluid feed and return part 50. The feed and return part 50 is positioned immediately below the pilot control unit 30. The positioner unit 40 comprises a housing 10 which is attached to the side of the pilot control unit 30. A rotation symmetrical cavity extends through the housing 10, and a cylinder pipe 12 of a non-magnetic material is secured in one end of the cavity within the cavity close to the pilot control unit 30. A copper wire winding or coil 13 is embedded in the outer surface of the cylinder pipe 12 so as to extend around the pipe, and a positioner means 11 is arranged slideably against the inner surface of the cylinder pipe 12 in a sealed manner. A control spindle 14 is attached to the end of the positioner means remote from the pilot control unit 30 for controlling a valve 60 attached to this end of the positioner unit 40. A spring assembly 15 to 18 is installed within the corresponding end portion of the cavity of the housing 10; the spring assembly tends to center the positioner means 11 when the means is moved in either direction. The housing 10 is attached to the side of the pilot control body 5 so that the axes of the pilot control spindle 3 and the posi¬ tioner means 11 are perpendicular to each other. The cylinder pipe 12, in turn, defines another cavity within it, and this cavity is divided by the posi- tioner means 11 into two pressure spaces A x 1 and B1 , of which one space A 1 acts on the front side (left side) of the positioner means 11, and the other space B 1 acts on the back side (right side) of the posi¬ tioner means 11. The pressure space A communicates with the boring 6 of the pilot control unit 30 by means of a conduit A extending through the body 5, and the pressure space Bl by means of a conduit B extending through the housing 10 and the body 5. The pressure space B is sealed by a seal 19 in the area of the housing 10 where the spring assembly 15 to 18 is positioned. The above-described cylinder pipe 12, the coil 13 around it, the positioner means 11 acting as a coil core, and the requisite electronics in the electronic unit 70, to which the coil is connected electrically, together form an entity by means of which the position of the positioner means 11 oper¬ ating in a piston-like manner is measured. The coil 13 and the means 11 are so positioned with respect to each other that the length of the portion of the means 11 remaining within the coil 13 varies with the position of the means 11. During operation within the measuring range, a certain length of the means 11 penetrated within the coil 13 corresponds to each position of the means 11. As the means 11 is made of a material in which eddy currents are liable to occur, the inductance of the coil 13 varies con¬ tinuously as a function of the position. The intens¬ ity of the created eddy currents - and thus the sensitivity of the sensor arrangement - can be affected e.g. by controlling the force line pattern of the magnetic field of the coil 13 and increasing the intensity of the force lines in a desired manner. In the present invention, the inductance of the coil 13 at each specific moment - and thus the posi- tion of the means 11 - is measured and converted into a pulse-length-modulated signal by means of a microprocessor. In structure, the actuator means shown in Figure 4a corresponds to the actuator means shown in Figures la, 2a and 3a with the exception of the arrangement of the position sensor. Here the position sensor 130 is wound on a spool 131 which is pushed over a cylinder pipe 120. This is another advanta- geous way of installing the position sensor around the cylinder pipe. The operating principle of the actuator means and the position sensor is not affected by this modification. The actuator means aggregate operates as follows: Figure la illustrates the rest state of the actuator means. When the proportional magnet 1 is currentless, the return spring 4 keeps the pilot control spindle 3 and the spindle 2 of the magnet 1 in the upper extreme position, a so-called safety position (Figure lb). The shoulder 8 of the pilot control spindle 3 keeps the pressure fluid conduit P closed, whereas the conduit A and the conduit B com¬ municate with the return fluid conduit T. The posi- tioner means 11 is maintained in its center position by the action of the centering spring 15, and it may be moved mechanically by an external force. In Figures 2a, 3a and 4b, the actuator means is shown in an operation state. In Figure 3a, current is supplied to the magnet 1 so that the magnet pushes the pilot control spindle 3 to a so-called center position (Figure 3b), in which the shoulder 7 pre¬ vents the flow between the conduit A and the return conduit T while allowing the flow between the pressure fluid conduit P and the conduit B. The posi¬ tion is sensed as described above by means of a signal processed by the means 11 and the micro¬ processor. The pilot control spindle 3 remains in this position to wait for the control signal, and it may move either downward (Figure 4b) or upward (Figure 2b), depending on the difference between the external control signal and the control signal supplied by the positioner means 11. As shown in Figure 2a, the pressure fluid con- duit P is connected to the conduits A and B when the pilot control spindle 3 moves upward due to the dif¬ ference between the external control signal and the position signal supplied by the positioner means 11. The shoulder 7 keeps the return fluid conduit T closed (Figure 2b). The positioner means 11 moves to the right due to the difference between the areas of the pressure spaces A 1 and B 1 until the signal supplied by the coil 13 corresponds to the control signal in magnitude, so that the pilot control spindle 3 returns to the center position (Figure 3b). The positioner means 11 remains in this new position as long as the control signal proportional to this position is maintained. The signal difference caused by the termination of the control signal displaces the pilot control spindle 3 from the center position (Figure 3b) to the position shown in Figure 4a, so that the pressure fluid conduit P is connected to the conduit B and the return conduit T to the conduit A. The positioner means 11 moves to the left, until the signal supplied by the coil 13 corresponds to the signal of the center position in magnitude, and so the pilot control spindle 3 returns to the center position (Figure 3b) . When the pilot control spindle 3 moves down- ward, as shown in Figure 4a, due to the difference between the external control signal and the position signal supplied by the positioner means 11, the pressure fluid conduit P is connected to the conduit B and the return conduit T is connected to the conduit A (Figure 4b). The positioner means 11 moves to the left due to the pressure difference between the pressure spaces A 1 and B 1 until the signal supplied by the coil 13 correspond to the control signal in magnitude, and the pilot control spindle 3 returns to the center position (Figure 3b). The po¬ sitioner means 11 remains in this new position as long as the control signal proportional to this posi¬ tion is maintained. The signal difference caused by the termination of the control signal displaces the pilot control spindle 3 from the center position (Figure 3b) to the position shown in Figure 2a, so that the pressure fluid conduit P is connected to the conduits A and B. The shoulder 7 keeps the return conduit T closed. The positioner means 11 moves to the right due to the difference between the areas of the pressure spaces A 1 and B 1 until the signal supplied by the coil 13 corresponds to the signal of the center position in magnitude, and the pilot control spindle 3 returns to the center position (Figure 3b). It is typical of the actuator means according to the invention that it operates in a volume flow controlled manner, so that when it is connected to a pressure source, its pressure is constantly the same as that of the pressure source. In other words, the entire pressure of the pressure source can immediate¬ ly be used to move the positioner means 11 when the control is started. If the volume flow control is compared with the pressure control acting against the spring, a considerable functional advantage is obtained. It is typical of a pressure-controlled device that the control pressure required to obtain a certain initial control position may be e.g. one fourth of the re- quired final pressure (initial pressure e.g. 6 bar, final pressure 25 bar); as is well-known, this causes operational disturbances and even prevents the oper¬ ation of the device due to viscosity problems when cold oil is employed.

Claims: Claims : 1. A proportional mechano-electronic actuator means for a device linearly controllable by a pressure fluid, the actuator means being intended to be connected between a pressure source (P) and the device (60) to be controlled, comprising: - a proportional magnet (1); - a pilot control spindle (3) arranged to be movable in a pilot control body (5) by means of the proportional magnet (1) for opening and closing dif¬ ferent pressure fluid conduits (A, B, P, T); - a positioner means (11) for the device (60) to be controlled, the positioner means (11) being linearly controllable in two directions by means of the pilot control spindle (3) so that the pilot control spindle (3) tends to keep the positioner means (11) at each particular moment in a pre¬ determined position corresponding to a control signal supplied by an electric control unit (70) of the actuator means so as to linearly control the device (60) to be controlled through a control spindle (14) or other similar external coupling device of the actuator means, c h a r a c t e r i z e d in that a position sensor (13; 130) electrically sensing the position of the positioner means (11) is provided in a substan¬ tially cylindrical means (12; 120) defining a space where the positioner means (11) moves, the position sensor comprising a winding fitted around said means (12; 120). 2. An actuator means according to claim 1, c h a r a c t e r i z e d in that the position sensor (13) is embedded in the outer surface of the cylinder pipe (12) positioned around the positioner means (11). 3. An actuator means according to claim 2, c h a r a c t e r i z e d in that the position sensor (130) is wound on a spool (131) which is pushed over the cylinder pipe (120). 4. An actuator means according to claim 2 or 3, c h a r a c t e r i z e d in that the cylinder pipe (12; 120) is of a non-magnetic material. 5. An actuator means according to any of claims 2 to 4, c h a r a c t e r i z e d in that a housing (10) of the positioner means (11) is attached to the side to the pilot control body (5) so that the axes of the pilot control spindle (3) and the positioner means (11) are substantially perpendicular to each other, and that the cavity defined by the cylinder pipe (12; 120) comprises pressure spaces (A 1 , B 1 ) acting on the front and the back side of the posi¬ tioner means (11), the pressure spaces communicating by means of one pressure fluid conduit (A, B) with a space in which the pilot control spindle (3) moves and which communicates with the pressure source (P).

Inventors: AHONOJA ILKKA, LUOMARANTA MARKKU, AHONOJA, ILKKA, LUOMARANTA, MARKKU
Applicants: NESTEPAINE AB OY, OY NESTEPAINE AB
Application year: 1992
Main classification: F15B13
IPC codes: F15B13, F15B15