Actuator of a paper or board machine

Abstract: The invention relates to an actuator comprising a motor (4) by which the shafts (1, 5, 7) of the actuator are driven. At least one magnet (2) is arranged in conjunction with the shaft (1, 5, 7). The actuator further comprises at least one Hall sensor (3), which generates pulses as the magnet (2) on the shaft (1, 5, 7) passes the Hall sensor (3) as the shaft (1, 5, 7) rotates. The pulses are used to define the position of the actuator in the linear direction (Fig. 2).

Description: The invention relates to an actuator for a paper or board machine in accordance with the preamble of claims 1 and 2. Actuators are used, for example, to control the flow of different media, such as water and steam, in different processes. The actuators control a valve, nozzle or the like supplying the medium. The actuator can be a motor, cylinder or the like, which can be controlled in many different ways, for example mechanically, electrically, hydraulically or pneumatically. US Patent 4 662 398 discloses a valve controlling the flow of steam and air to the steam box of an apparatus for drying a fiber web. The valve is controlled by a stepping motor. The control arrangement of the stepping motor is very complicated, and it is uncertain whether the motor will operate reliably in the very difficult process conditions of a paper machine. Further, the positioning data of the valve, defined solely on the basis of the control of the stepping motor, is rather unreliable. DE Utility Model 29 701 674 discloses an actuator comprising a valve that is controlled by a brushless electrical motor. The position of the rotor of the brushless motor is measured by means of Hall sensors, and so the position of the actuator is also defined on the basis of the pulses generated by the Hall sensor. The publication teaches that the Hall sensor is also particularly used to effect the rotating motion of the motor. The control system of the brushless motor is complicated, and the rotation of the rotor is also difficult and complicated to measure. It is thus out of the question to use the sensor defining the position of the rotor and the brushless motor in the processing conditions of a paper machine. FI Patent 85 731 discloses actuators whose spindles are adjusted by stepping motors. The position of the spindles is measured by LVDT sensors. The control arrangement of the stepping motor is complicated and cumbersome. The LVDT sensor endures the process conditions of a paper machine rather poorly, and it is susceptible to malfunction. The signal generated by the LVDT sensor is also very weak, and for example due to great temperature dependence, the accuracy of the sensor is rather poor. GB Patent Application 2 225 415 discloses a fluid flow valve controlled by a stepping motor. The position of the valve can be measured by an optical shaft encoder. The optical encoder requires a complicated and sensitive electronic arrangement, which is difficult to arrange in conjunction with a paper machine: the optical encoders do not endure the process conditions of a paper machine. Document DE 37 26 885 A discloses an actuator comprising a motor which drives a shaft when the position of the actuator in the linear direction is adjusted by rotating the shaft. For measuring the rotation of the shaft, to generate a pulse output proportional to the rotation of the shaft, and for defining the position of the actuator in the linear direction, a sensor is used comprising a Hall sensor which generates a pulse when a detection point of the shaft revolves past the Hall sensor. Document DE 195 06 938 A1 discloses a device for measuring the rotating angle of a rotating member. This device comprises two detection point wheels in engagement with a cogwheel wherein the rim of the cogwheel is larger than the rim of the detection point wheels wherein the detection point wheels cooperate with sensors detecting the rotation of the detection point wheels to measure the rotating angle of the rotating member with high accuracy. The object underlying the invention is to provide an actuator of a paper or board machine ensuring a high accuracy of the actuator by means of a reliable measurement of the linear position of the actuator and allowing a compact design of the actuator. This object is solved by the features of claims 1 and 2. The invention is described in greater detail in the attached drawings, in which Fig. 1 is a general schematic cross-sectional view of a principle of a measurement arrangement according to the invention at the shaft of the actuator, seen from the end of the shaft, Fig. 2 is a schematic cross-sectional side view of an actuator according to the invention, and Fig. 3 is a schematic cross-sectional side view of another actuator according to the invention. Fig. 1 shows a shaft 1 of the actuator. The shaft 1 of the actuator can be either the control shaft of the actuator or the shaft of the motor. Magnets 2 are arranged on the shaft 1. The apparatus further comprises a Hall sensor 3, which is arranged at the front of the end of the shaft 1. When the motor of the actuator is driven, the shaft 1 rotates, whereby the magnets 2 revolve past the Hall sensor 3. When the magnet 2 passes the Hall sensor 3, the Hall sensor 3 generates a pulse. The positioning of the actuator is proportional to the rotating motion of the shaft 1: the interval between the pulses corresponds to a certain change in the positioning of the actuator. The position of the actuator can thus be defined on the basis of the pulses. Fig. 2 shows an actuator in which the magnets 2 are arranged at a shaft 5 of a motor 4. The shaft 5 of the motor is provided with a cogwheel 6, in which the magnets 2 are arranged. The cogwheels 6 transmit the rotating motion of the shaft 5 of the motor, turning it into the rotating motion of a control shaft 7 of the actuator. The rotation of the control shaft 7 adjusts the position of the valve or another actuator in the linear direction, and the adjustment can be effected, for example, by cogwheels or gearing or other shafts. For the sake of clarity, the attached drawings do not show the valve nor the gearing nor the other shafts. The actuator of the invention can be an actuator known per se, used, for example, in a steam box, head box or moisturizer or some other part of a paper or board machine. It is previously known to use controllable profiling equipment to improve the cross profile variables of the paper web, the equipment being usually divided into control sections crosswise of the web. Each valve, nozzle, etc. that is in the control section of the profiling equipment and affects the variables of paper is controlled by actuators arranged in the section. Any changes effected by the actuators and elements, for example a motion, force, flow, or the like, have an indirect effect on the cross profile characteristics of paper, which include basis weight, moisture, thickness and gloss. The motion, force or some other change mentioned above can be effected in the element by the actuators. The actuator of the invention is particularly useful in the control of the steam supply of the steam box of a paper machine. The amount of steam supplied from the steam box onto the surface of the web is currently adjusted by the pressure of the supplied steam. The pressure is difficult to adjust accurately, and the amount of steam flowing through individual steam nozzles cannot be defined. The pressure is defined by an analogue gauge, which is expensive. The solution of the invention is cheap and very accurate, since the precise position of the steam control shaft is known. The amount of steam is calculated on the basis of pulse data, whereby no separate gauges are needed. The amount of steam is adjusted quickly and accurately by means of the pulse data and the control shaft. The invention thus makes it possible to replace expensive gauges, and thereby save money. The motor 4 is preferably a synchronous motor with a simple control arrangement. The actuator can thus be rendered simple and reliable. Arranged in the manner shown in Fig. 2, the Hall sensor 3 and the magnets 2 and the entire actuator can be encased in a housing, whereby they resist wear and also endure well the processing conditions of a paper machine. Fig. 3 shows a solution in which the cogwheel 6 of the shaft 5 is also arranged to rotate a detection point wheel 8. The magnets 2 are arranged in the detection point wheel 8. The cogwheel 6 and the detection point wheel 8 have preferably toothed edges. The rim of the cogwheel 6 of the shaft 5 is larger than the rim of a shaft 8a of the detection point wheel 8, and so when shaft 5 rotates, the detection point wheel 8 rotates faster than shaft 5. If the ratio of the rim of the shaft 8a of the detection point wheel 8 to the rim of the cogwheel 6 is 1/20, one turn of shaft 5 corresponds to twenty turns of the detection point wheel 8. If, for example, five magnets are arranged in the detection point wheel 8, a hundred pulses are obtained by the Hall sensor 3 on one turn of shaft 5. Typically, the motion corresponding to one pulse is 1 micrometer, i.e. the pulses are very frequent, whereby the position of the actuator can be defined very accurately on the basis of the pulses. The drawing and the associated description are intended only to illustrate the idea of the invention. The invention can vary in its details within the scope of the claims. The number and positioning of the Hall sensors and magnets can thus vary according to the need. Further, a magnet need not necessarily be arranged in conjunction with the shaft, but the Hall sensor can also detect another kind of detection point in the shaft, such as a notch or protrusion or some other asymmetrical point in the shaft, and thereby generate a pulse as the detection point passes the sensor. Further, the detection point can consist of non-magnetic material: the Hall sensor detects the passing of such material if the rest of shaft is made of magnetic material.

Claims: An actuator for a paper or board machine and an apparatus for adjusting the position of the actuator in the linear direction comprising a motor (4); a shaft (1, 5, 7) driven by the motor (4), the position of the actuator in the linear direction being adjusted by rotating the shaft (1, 5, 7) by the motor (4); and a sensor which is arranged to measure the rotation of the shaft (1, 5, 7) and to generate a pulse output proportional to the rotation of the shaft (1, 5, 7) to define the position of the actuator in the linear direction, wherein at least one detection point comprising at least one magnet (2) is arranged in conjunction with the shaft (1, 5, 7) and that the apparatus comprises at least one Hall sensor (3), which generates a pulse when the detection point of'the shaft (1, 5, 7) revolves past the Hall sensor (3), characterized in that said shaft (5) of the motor (4) is provided with a cogwheel (6) in which magnets (2) are arranged, wherein said cogwheel (6) transmits the rotating motion of the shaft (5) of the motor (4) to a control shaft (7) of the actuator. An actuator for a paper or board machine and an apparatus for adjusting the position of the actuator in the linear direction comprising a motor (4); a shaft (1, 5, 7) driven by the motor (4), the position of the actuator in the linear direction being adjusted by rotating the shaft (1, 5, 7) by the motor (4); and a sensor which is arranged to measure the rotation of the shaft (1, 5, 7) and to generate a pulse output proportional to the rotation of the shaft (1, 5, 7) to define the position of the actuator in the linear direction, wherein at least one detection point comprising at least one magnet (2) is arranged in conjunction with the shaft (1, 5, 7) and that the apparatus comprises at least one Hall sensor (3), which generates a pulse when the detection point of the shaft (1, 5, 7) revolves past the Hall sensor (3), characterized in that said shaft (5) of the motor (4) is provided with a cogwheel (6), which transmits the rotating motion of the shaft (5) of the motor (4) to a control shaft (7) of the actuator, wherein magnets (2) are arranged at a detection point wheel (8) engaged with said cogwheel (6), wherein the rim of said cogwheel (6) is larger than the rim of that part of said detection point wheel (8) which comes into contact with said cogwheel (6) . An actuator as claimed in claim 1 or 2, characterized in that the Hall sensor (3) is arranged in conjunction with the shaft (5) of the motor (4). An actuator as claimed in any one of the preceding claims, characterized in that the motor (4) is a synchronous motor.

Inventors: SANAKSENAHO JUHA, SAUNISTO KIMMO, SORSA JUKKA, SANAKSENAHO, JUHA, SAUNISTO, KIMMO, SORSA, JUKKA
Applicants: METSO AUTOMATION OY
Application year: 1999
Main classification: G01D5
IPC codes: G01D5, G05B19