TRANSPORTATION SYSTEM OF A FLOATED-CARRIER TYPE

Abstract: A transportation system of a floated-carrier type according to this invention includes a carrier (2) capa­ ble of running along guide rails (l) with a cargo and load carried thereon. A magnetic unit (l2-l to l2-4) is mounted on the carrier (2) to float the carrier (2) from the guide rails (l). A slowing-down device (4) is pro­ vided to slow down the carrier (2) when the carrier (2) is just about to enter into a stop position. Projec­ tions (35-l to 35-4) of ferromagnetic material are pro­ vided on the side of predetermined portions of guide rails (l) which the magnetic unit (l2-l to l2-4) of the carrier (2) confronts when the carrier (2) is stopped in the stop position. The magnetic unit (l2-l to l2-4), together with the guide rails, establishes a magnetic circuit. The magnetic resistance in the magnetic cir­ cuit is smaller at the predetermined portions of the guide rails where the aforementioned projections (35-l to 35-4) are provided than at other portions of the guide rails. When, in this case, the carrier (2) arri­ ves substantially at the stop position, the magnetic flux due to the magnetic unit flows through the afore­ mentioned magnetic circuit in an increasing amount, assuring an increased attractive force between the magnetic unit (l2-l to l2-4) and the predetermined por­ tions of the guide rails (2) where the projections (35-l to 35-4) are provided. As a result, the carrier (2) is attracted toward the location of these predetermined portions of the guide rails (l) so that it is positioned precisely in the stop position.

Description: This invention relates to a transportation system of a floated-carrier type and, in particular, a trans­ portation system of a floated-carrier type including means for positioning the carrier exactly in a stop position. To increase the degree of office or factory automa­ tion, transportation systems have recently been installed in some buildings. Such transportation systems are used to transport slips, documents, cash, samples, or the like, between a plurality of locations in the buildings. In order to avoid spoiling the environment of the offices or the factories, the transportation systems of this system are expected to produce neither dust nor a high level of noise. In one such conventional transportation system described in EPC Appl. Ser. No. 85l05028,6 field on April 25, l985, by applicant hereof, a carrier is mag­ netically suspended, in a non-contact manner, from a guide rail by means of an electromagnetic attractive force acting between the carrier and the rail, when the carrier is propelled along the rail. Generally, the carrier is either propelled, or braked, by causing the reaction plate mounted on the carrier to be energized by virtue of the stator of a linear induction motor. In the transportation system it is required that, when the carrier is stopped in a predetermined stop position (station), it is positioned exactly at that location. This occurs in the situations where, for example, the cargo is loaded onto the carrier at the location of the station or the battery of the carrier is charged up. As such a positioning means use may be made of the following conventional means. As the first posi­ tioning means, at the stop position, a stopper means is provided which is actuated by a corresponding air cylin­ der and sandwiches the carrier. In this case, upon the arrival of the carrier, which is caused to coast along after the carrier has been slowed down by virtue of a stator, substantially at the stop position, it is sand­ wiched by the stopper means, so that the carrier is positioned exactly at the stop position. A second type of positioning means may be electromagnets, provided at the stop position an a guide rail, which position the carrier by magnetically attractive force between them­ selves and iron plate pasted on the carrier. A third positioning means is composed of two stators which are provided on both ends of the stop position in the direc­ tion of run of the carrier. In this case, the two sta­ tors are excited in the opposite direction each other so as to position the carrier in proper place. This type of positioning means is disclosed in Japanese Patent Disclosure (KOKAI) No. 57-3588 and Japanese Patent Publication (KOKOKU) No. 6l-55338. However, when the first positioning means is used, the transportation system cannot achieve its function that the carrier is magnetically suspended in a comple­ tely non-contact manner from guide rail. The second and third positioning means involves the problem of requiring a large-sized equipment. It is accordingly the object of this invention to provide a transportation system of a floated-carrier type which can stop a carrier exactly in a stop position through a simpler positioning means. According to this invention, there is provided a transportation system of a floated-carrier type as set forth below. Guide rails, which are formed of ferro­ magnetic material, extend in the longitudinal direction. A carrier travels along the guide rails with a cargo carried thereon. A magnetic unit includes electro­ magnets so arranged as to confront the lower surface of the guide rail with an air gap left therebetween, and floats the carrier from the guide rail. The transporta­ tion system further includes a device for running the carrier along the guide rails, and slowing down it when the carrier is just arriving to a stop position. Projections of ferromagnetic material are provided on the side of predetermined portions of the guide rails which the magnetic unit of the carrier confronts when the carrier has been stopped to the stop position. The magnetic unit, together with the guide rails, creates a magnetic circuit. The magnetic resistance in the magnetic circuit is smaller at the predetermined por­ tions of the guide rails where the projections are pro­ vided as set forth above than at other portions of the guide rails. Accordingly, when the carrier arrives substantially at the stop position, the magnetic flux flows through the aforementioned magnetic circuit in an increasing amount. When this is done, an increased attractive force due to the increased magnetic flux acts between the magnetic unit and the predetermined portions of the guide rails where the projections are provided. As a result, the magnetic unit is attracted toward the predetermined portions of the guide rails, so that it is stopped exactly in the stop position through such simpler positioning means. This invention can be more fully understood from the following detailed description when taken in con­ junction with the accompanying drawings, in which: Fig. l is a perspective view showing a transporta­ tion system of a floated-carrier type according to an embodiment of this invention; Fig. 2 is a sectional view showing a magnetic unit for floating the carrier from guide rails; Fig. 3 is a sectional view showing the side por­ tions of the guide rails where projections are formed; Fig. 4 is a plan view showing a stop position where the carrier is stopped on the transportation system as shown in Fig. l; Fig. 5 is a block diagram showing a control circuit for stopping the carrier; Fig. 6 is a flowchart showing the process for stopping the carrier; and Figs. 7 and 8 each show a plan view showing the operation of the transportation system when the carrier has been stopped. In a transportation system of a floated-carrier type, as shown in Fig. l, a pair of guide rails l longi­ tudinally extend parallel to each other. Carrier 2 is suspended below the pair of guide rails, under a magnet­ ic attractive force, in a non-contact manner from guide rails l. Carrier 2 is propelled by a liner induction motor along guide rails l. Guide rail l is fixed to the inner surface of the top wall of guide rail cover 3l which has an inverted U-shape in cross-section. Guide rail cover 3l guards moving carrier 2 with a spacing defined therebetween. Carrier 2 includes supporting plate ll situated below guide rail l in a manner to face the undersurface of guide rail l and carrier box l3 supported by sup­ porting plate ll. Four magnetic units l2-l to l2-4 are located at each of four corners of supporting plate ll. Carrier 2 is levitated by magnetic units l2-l to l2-4, in the non-contact manner from guide rails l. Reaction plate l4 is located in the middle of the surface of supporting plate ll to face stator 4 of a linear induction motor. Stator 4 is located under guide rail cover 3l. Upon the excitation of stator 4, a propelling force acts upon carrier 2. When, on the other hand, a traveling magnetic field is produced on stator 4 in a direction opposite to the aforementioned propelling direction, carrier 2 suffers a braking force and is brought to a stop. Reflection plate l5 is provided at each side surface of carrier box l3 in which case light beams emitted from sensors 36-l to 36-4 as set forth below, are reflected on reflection plate l5. As is shown in Fig. 2, each magnetic unit l2-l ∼ l2-4 is provide with yokes 25, facing guide rail l. Conducting wires are wound around yokes 25, thus forming coils 22, 23. Air gap P is defined between the top face of each yoke and the lower surface of rail l. Permanent magnet 24 is used to couple yokes 25 magnetically. Thus, permanent magnet 24, yokes 25, gaps P, and rail l constitute a magnetic circuit. Each magnetic unit is further provided with a gap sensor 27 for detecting the amount of clearance of gap P. In a station, i.e., a predetermined stop position, as shown in Fig. l, four projections 35-l to 35-4 are formed on the side of predetermined portions of guide rails l. When carrier 2 stops in its stopping position, magnetic units l2-l to l2-4 confront the corresponding the predetermined portions of guide rails l. That is, the distance between projections 36-l and 36-2 (or 36-3 and 36-4) are set equal to that between the corresponding two magnetic units l2-l and l2-2 (or l2-3 and l2-4). Carrier 2 is stopped exactly in the stop position by projections 36-l to 36-4. As set forth above, mag­ netic units l2-l to l2-4 and guide rails l create a magnetic circuit in which case a magnetic resistance is smaller at the predetermined portions of guide rails l where projections 35-l to 35-4 are formed than at other portions of guide rails l. When carrier 2 substantially reaches the stop position, the magnetic flux flowing through the aforementioned magnetic circuit is augmented, thus increasing a magnetic attractive force between magnetic units l2-l to l2-4 and the predetermined portions of guide rail. As a result, magnetic units are attracted toward the predetermined portions of guide rails l, and then carrier 2 is stopped exactly at the stop position. Projections 35-l to 35-4 are thin-walled as shown in Fig. 3 so that, when carrier 2 passes through the stop position, projections 35-l to 35-4 never provide any adverse influence over the run of carrier 2. As shown in Figs. l and 4, optical sensors 36-l to 36-4 of reflection type are so located as to properly confront reflection plates l5 which are formed on both outer side surface of carrier 2. A pattern of equidis­ tant vertical stripes is formed on reflection plates l5 facing sensors 36-3 and 36-4 in particular. The speed of carrier 2 is detected through the detection of that stripe pattern by sensors 36-3 and 36-4. Sensors 36-l and 36-2 detects whether or not carrier 2 is located in the aforementioned predetermined position. A linear motor controller, not shown, includes control circuit 200, as shown in Fig. 5, which excites stator 4 so as to stop carrier 2 in the stop position. Control circuit 200 includes aforementioned sensors 36-l to 36-4, microcomputer 204 and inverter 206. Between either one of sensors 36-3 and 36-4 and microcomputer 204, are interposed, switching circuit 20l, F/V converter 202 and A/D converter 203 in that order. D/A converter 205 is connected between microcomputer 204 and inverter 206. The detection signals sensors 36-l and 36-2 are input directly to microcomputer 204, while the detection signals from sensors 36-3 and 36-4 are supplied to switching circuit 20l. Upon receipt of a signal from microcomputer 204, switching circuit 20l has its con­ tacts switched to either one of terminals so that a corresponding one signal may be selected. This is because, upon the movement of carrier 2, either one of sensors 36-3 and 36-4 which are located at predetermined interval, detects the speed of carrier 2. The selected detection signal is supplied to F/V converter 202 where it is converted to a voltage level corresponding to the speed of carrier 2. The voltage of F/V converter 202 is supplied to A/D converter 203 where it is converted to a digital signal. The digital signal is supplied to microcomputer 204. Microcomputer 204 recognizes the position of carrier 2 on the basis of the detection signals of sen­ sors 36-l and 36-2 and recognizes the speed of carrier 2 on the basis of the detection signals of sensors 36-3 and 36-4. By so doing, microcomputer 204 delivers sig­ nal 204a to inverter 206 directly, and digital signal 204b to D/A converter 205. Digital signal 204b is transformed into analog signal 204c by D/A converter 205. Microcomputer 204 delivers a signal to switching circuit 20l, as set forth above. Inverter 206 puts out phase alternating current to stator 4, based on the value of signal 204c in which case the value of [excitation voltage/excitation frequency] is maintained constant, and at the same time it changes the phase of the alternating current, based on the value of signal 204a. Such action of inverter 206 generates the magnetic field, which travels at the speed corre­ sponding to signal 204b and in the direction correspond­ ing to signal 204a, on stator 4. At that time, if reaction plate l4 confronts stator 4, it receives the electromagnetic force which has the strength correspond­ ing to the speed of the magnetic field and the same traveling direction as the magnetic field. As the result of the above, microcomputer 204 can control the electromagnetic force, given to reaction plate l4 by stator 4, with signals 204a and 204b. The operation of the transportation system of a floated-carrier type, will now be explained below. Carrier 2 is suspended from guide rails l, in a non-­ contact manner, by means of a magnetic attractive force acting between magnetic units l2-l to l2-4 and guide rails l. In this embodiment, units l2-l to l2-4 are controlled by so-called zero-power control device, so that the minimum necessary electric current is supplied to coils l3 when carrier 2 is made to float. In other words, four permanent magnets 24 always generate an attractive force equal to the total weight of carrier 2 itself and the load. At the same time, coils 22, 23 are excited, so as to maintain the air gap clearances with which the attractive forces between the permanent magnet and rails balance with the total weight of the carrier itself and the load. Coils 22, 23 serve to subordinately cause carrier 5 to float. If the total weight of car­ rier 2 is changed by the load, current fed to coils l3 is controlled so that gap P is adjusted to a distance such that the total attractive forces between permanent magnet 24 and guide rails l balance to the total weight of carrier 2 and the load. In other words, by control­ ling the current supplied to the coils, clearance of gap P is adjusted to a distance such that carrier 2 is caused to float by means of the magnetic energy of permanent magnet 24 only, despite the existence of disturbances. (The zero-power control device described in EPC Appl. Ser. No. 85l05028,6 field on April 25, l985, by appli­ cant hereof.) As is shown in Fig. l, if stator 4 is excited when there is carrier 2 floated just beneath stator 4, reac­ tion plate l4 receives an electromagnetic force from stator 4, and carrier 2 the begins to travel along guide rails l. The carrier 2 on travel receives a successive propelling force from the stators, which is located along guide rails l at predetermined intervals. When carrier 2 is just about to reach the station, two situations exist: (l) carrier is passed through the station and (2) carrier 2 is caused to stop at the sta­ tion. In the former case (l), carrier 2 continues to travel under the action of stator 4 and, if in this case the speed of carrier 2 exceeds a predetermined level, carrier 2 is allowed to run without the action of stator 4 in which case carrier 2 simply runs past the station. The process of stopping carrier 2 at the station (the latter case (2)) will now be explained below with reference to the flowchart of Fig. 6. Let be assumed that, as shown in fig. 7, carrier 2 approaches at a certain speed from left to right. At step Sl0l, the outputs of sensors 36-l and 36-2 are read out, and at steps Sl02 and l2l, it is judged whether or not sensors 36-l and 36-2 are ON. Before carrier 2 moves to the stop position, sensors 36-l and 36-2 are OFF and, at this time, the process skips over to step Sl09 where stator 4 is not excited. When carrier 2 is just about to enter into the sta­ tion, sensor 36-l is rendered ON to produce a detection signal. At step Sl03, microcomputer 204 causes the con­ tact of switching circuit 20l to be switched to the ter­ minal of switch 36-3 on the basis of that detection signal. At step Sl04, the detection signal of sensor 36-3 is supplied to microcomputer 204. At step Sl05, microcomputer 204 calculates a difference ΔV (= V - V₀) between the speed V and the reference speed V₀ of the carrier. At step Sl06, it is judged whether or not ΔV ≦ 0 and, if ΔV is positive, the process goes to step Sl3l where inverter 206 excites stator 4 so as to generate the magnetic field traveling on stator 4, in an arrow-indicated direction of Fig. 7, with the frequency whose magnitude is proportional to the difference ΔV. By so doing, carrier 2 starts to slow down. The process at step Sl3l goes back to step Sl0l where the repetition is made until ΔV ≦ 0. During the process, at step Sl2l sensor 36-2 is turned ON when carrier 2 comes to the position where it traverses the light beam which has been emitted from sensor 36-2. At step Sl22, microcom­ puter 204, upon receipt of the direction signal from sensor 36-2, causes the contact of switching circuit 20l to be switched to the side of sensor 36-4. Thus the data presenting the carrier speed is delivered via sen­ sor 36-4 to microcomputer 204. If ΔV ≦ 0 at step Sl06, the outputs of sensors 36-l and 36-2 are read out at step Sl07. At step Sl08 it is judged whether or not the outputs of sensors 36-l and 36-2 are both rendered ON. If the answer is in the negative, the traveling direction of the magnetic field, as well as the excitation frequency, is so determined, at step Sl4l, that carrier 2 is moved to the stop posi­ tion at the speed of V₀. Thus the process goes back to step Sl0l. For, example, if carrier 2 reaches the posi­ tion, as shown in Fig. 7, under the situation of ΔV ≦ 0, the carrier moves to the stop position by receiving a propelling force opposite to the direction as indicated by an arrow in Fig. 7. At this time, if the situation changes to ΔV > 0, the carrier speed V goes back to V₀ by receiving a propelling force opposite to the carrier running direction. In addition, in the case that the speed of carrier doesn't become below V₀ until the carrier pass the predetermined stop position, the carrier encounters a propelling force opposite to that in the carrier running direction. For this reason, there is sometimes that case where, while being recipro­ cated around the stop position as a center, carrier 2 is approached to there. It step Sl08, when both sensors 36-l and 36-2 are concurrently turned ON, carrier 2 is judged as being located substantially at the predetermined stop position and, at step Sl09, inverter 206 stops exciting stator 4 excitation. At this time an attractive force is in­ creased between magnetic units l2-l to l2-4 and those predetermined portions of guide rails 35-l to 35-4, where projections 35-l to 35-4 are provided. As a result, magnetic unit are attracted at those predeter­ mined portions of guide rails, so that it is stopped to be located exactly in the predetermined stop position as shown in Fig. 8. In this connection it is to be noted that the speed V₀ is set to a sufficiently low level at which carrier 2 can be positioned by projections 36-l to 36-4. According to this invention, the excitation fre­ quency for stator 4 is continuously controlled in a manner to be proportional to the speed difference V-V₀. For this reason, carrier 2 can swiftly be slowed down even if it enters into the station within a predeter­ mined range of speed. This invention is not restricted to the aforemen­ tioned embodiment. In the aforementioned embodiment, projections 35-l to 35-4 are formed integral with guide rails l. However, projections 35-l to 35-4 may be formed separate form guide rails l in which case they are jointed to guide rails l by screws or welding. These projections may be formed such that they extend inwardly of guide rails l. According to the aforementioned embodiment, the guide rails are comprised of a pair of lines. Alterna­ tively, however, the pair of lines may be replaced by either one or three or more lines. Furthermore, the magnetic unit may be so constructed that the carrier is caused to float by means of the magnetic force of the coils only, without any permanent magnet.

Claims: 1. A transportation system of a floated-carrier type comprising: guide rails (l) made of ferromagnetic material and extending in a longitudinal direction; a carrier (2) capable of running along the guide rails with a cargo carried thereon; a magnetic unit (l2-l to l2-4), mounted on the carrier (2) and having an electro­ magnet (22, 23) confronting the lower surfaces of the guide rails (l) with an air gap defined therebetween, whereby said carrier (2) is floated relative to the guide rails (l) in a non-contact manner; and means (4) for running said carrier along the guide rails and for slowing down the carrier (2) when the carrier (2) is just about to enter into a stop position, characterized by further comprising member (35-l to 35-4) made of ferromagnetic material and provided on the side of the predetermined portion of the guide rail (l), the predetermined portion being located such that the magnetic unit (l2-l to l2-4) of the carrier (2) con­ fronts the predetermined portion when the carrier (2) has stopped at a stop position, whereby the predeter­ mined portion has a lower magnetic resistance, so that the magnetic unit (l2-l to l2-4) is attracted at the predetermined portion, thus the carrier (2) being allowed to be positioned at the stop position. 2. The transportation system according to claim l, characterized in that said member constitutes projection (35-l to 35-4) which is provided on the side of the predetermined portion of said guide rail (l). 3. The transportation system according to claim 2, characterized in that two projections (35-l to 35-4) are provided on said guide rails (l) and are separated in a longitudinal direction, and two magnetic units (l2-l and l2-2, or l2-3 and l2-4) are provided on the carrier (2) and are separated in the longitudinal direction, in which a distance between said two projections (35-l and 35-2 or 35-3 and 35-4) is sub­ stantially equal to that between said two magnetic units (l2-l and l2-2, or l2-3 and l2-4). 4. The transportation system according to claim 2, characterized in that a pair of guide rails (l) are pro­ vided with a pair of said projections (35-l to 35-4), respectively, and four magnetic units (l2-l to l2-4) are located at each corner of said carrier (2). 5. The transportation system according to claim l, characterized in that said means for slowing down the carrier (2) has a stator (4) for a linear induction motor and a reaction plate (l4) mounted on said carrier (2) and receiving a propelling force from the stator. 6. The transportation system according to claim 5, characterized in that said means for slowing down the carrier includes: a first sensor means (36-l, 36-2) for detecting the position of said carrier (2), in the stop position, and delivering a detection signal; a second sensor means (36-3, 36-4) for detecting the speed of said carrier (2); an inverter (206) for controlling a three phase alternating current which is supplied to the stator (4) to excite said stator (4), while switching the phase of said three phase alternating current; and a microcomputer (204) for receiving first and second detection signals and supplying to said inverter (206) signals having information about an excitation frequency, an excitation voltage for the stator (4) and the phase for said three phase alternating current. 7. The transportation system according to claim 6, characterized in that in the stop position, said first sensor means has a pair of first optical sensors (36-l, 36-2) which are located in the longitudinal direction over a distance substantially equal to the longitudinal distance of said carrier (2). 8. The transportation system according to claim 6, characterized in that the second sensor means have a pair of second optical sensors (36-3, 36-4) being provided in the stop position of said carrier (2) and in the longitudinal direction over a distance substan­ tially equal to the longitudinal distance of said carrier (2); a plurality of stripes (l5) being formed at a predetermined interval on the side surface of said carrier; said slowing-down means having a switch­ ing circuit (20l) which supplies to said microcomputer (204) either one of two detection signals which are delivered from said pair of second optical sensors (36-3, 36-4). 9. The transportation system according to claim 2, characterized in that said member (35-l to 35-4) is formed integral with said guide rails (l). l0. The transportation system according to claim l, characterized in that said magnetic unit (l2-l to l2-4) is composed of permanent magnets (24) capable of pro­ viding magnetic energy, with which carrier (2) can be kept floating against the weight thereof and the load thereon, and electromagnets (22, 23) adapted to be excited so as to maintain an air gap clearance, with which the magnetic attractive force acting between the permanent magnets (24) and the ferromagnetic guide rail (l) balances with the total weight of the carrier (2) itself and the load, regardless of a change of the load weight.

Inventors: AZUKIZAWA, TERUO C/O PATENT DIVISION, MORISHITA, MIMPEI C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1987
Main classification: B65G54
IPC codes: B60L13, B65G54