KR20070000030A - Automatic guided vehicle for conveying cassette and method for conveying cassette - Google Patents

Abstract

An AGV(Automatic Guided Vehicle) and a method for conveying a cassette are provided to correct the positional error of a slide, thereby preventing the damage of substrates within a cassette during convey of the cassette, by using a position sensor of the slide and a mark plate of the cassette. A cassette(150) contains a plurality of substrates, and a mark plate(152) is attached on a rear surface of the cassette. The cassette is mounted on a mounting part(320). A robot arm(330) is formed under the mounting part, and loads the cassette to process apparatuses for respective process steps. The robot arm has a first position sensor(337), which reads information of the mark plate to sense the position of the cassette. A body supports the mounting part and the robot arm. A telecommunication sensor(350) is formed at one side of the body, and tele-communicated with adjacent stockers or apparatuses. A second position sensor(340) senses whether the stockers or the apparatuses are adjacent to desired regions or not. A conveyer is formed under the body.

Description

Automatic guided vehicle for conveying cassette and method for conveying cassette

The present invention relates to an automatic conveying apparatus, and more particularly, to an automatic cassette conveying apparatus and a cassette conveying method for stably transporting a cassette by accurately detecting a mechanical position on a cassette basis.

As the information society develops, the demand for display devices is increasing in various forms.In recent years, liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed. Various flat panel display devices have been studied, and some are already used as display devices in various devices.

Among them, LCD is the most widely used as a substitute for CRT (Cathode Ray Tube) for the use of mobile image display device because of the excellent image quality, light weight, thinness, and low power consumption, and mobile type such as monitor of notebook computer. In addition, it is being developed in various ways such as a television for receiving and displaying a broadcast signal, a monitor of a computer.

Such a liquid crystal display may be classified into a liquid crystal panel displaying an image and a driving unit for applying a driving signal to the liquid crystal panel.

1 is an exploded perspective view illustrating a part of a general liquid crystal display panel.

As shown in FIG. 1, the liquid crystal display panel has a predetermined space and has a liquid crystal layer injected between the first and second substrates 1 and 2 and the first and second substrates 1 and 2 bonded together. 3) consists of.

Here, the first substrate 1 (TFT array substrate) includes a plurality of gate lines 4 arranged in one direction at regular intervals and at regular intervals in a direction perpendicular to the respective gate lines 4. A plurality of pixel electrodes 6 and the gate formed in a matrix form in each of the pixel regions P defined by crossing the plurality of data lines 5 and the gate lines 4 and the data lines 5. A plurality of thin film transistors T, which are switched by the signal of the line 4 and transfer the signal of the data line 5 to the pixel electrodes P, are formed.

The second substrate 2 (color filter substrate) includes a black matrix layer 7 for blocking light in portions other than the pixel region P, and R, G, and B color filter layers for expressing color colors. 8 and a common electrode 9 for implementing an image are formed.

Of course, in the transverse electric field type liquid crystal display device, the common electrode is formed on the first substrate 1.

The liquid crystal display having the above structure includes a process of manufacturing a thin film transistor array on the first substrate 1, a process of manufacturing a color filter array on the second substrate 2, and the first and second substrates 1. , 2) adhering the liquid crystal, injecting and sealing the liquid crystal between the two bonded substrates, testing and repairing each liquid crystal panel in which the liquid crystal is injected, and back light on the good liquid crystal panel It is manufactured through a process of manufacturing a liquid crystal display module by mounting a lamp and a driving circuit.

As described above, the substrate is subjected to various processes to be completed as a liquid crystal display device, and an automatic guided vehicle is used to transport the substrate to equipment for performing each process.

At this time, in order to increase the conveyance efficiency of the automatic conveying apparatus, after storing the plurality of substrates in a cassette that can accommodate, the automatic conveying apparatus conveys the cassette.

2 is a front view showing a cassette automatic conveying apparatus according to the prior art.

As shown in FIG. 2, a cassette 17 in which a plurality of substrates are accommodated, a mounting portion 15 on which the cassette 17 is mounted, and a lower portion of the mounting portion 15 are provided on the mounting portion 15. Robot arm 11 for loading the mounted cassette 17 into the process equipment provided in each process step, a body portion 16 for supporting the mounting portion 15 and the robot arm 11, and the body portion A communication sensor 12 provided on one side of the communication device 12 for communicating with an adjacent stocker or process equipment, and a position detection sensor 13 for sensing that a proximity to a desired position of the stocker or process equipment is provided; The wheel 14 provided in the lower part of 16 is comprised.

Here, the robot arm 11 is composed of a plurality of slides (11a) and a drive shaft (11b) for rotating the slide (11a) up and down and 180 ° is connected to the lower portion of the slide (11a).

The operation of the cassette automatic conveying apparatus according to the related art configured as described above will be described in detail as follows.

3 is a plan view of a process line for explaining a cassette conveying process of a conventional automatic cassette conveying apparatus.

As shown in FIG. 3, the cassette automatic conveying apparatus AGV moves to the stocker 23 in which the cassette containing the several board | substrate necessary for each process equipment 21a, 21b was accommodated.

Here, by using the position detection sensor 13, the mark plate is read in the front part of the stocker 23, thereby accurately positioning the front of the stocker 23.

Subsequently, by communicating with the stocker 23 using the communication sensor 12, the robot arm 11 which loads the cassette 17 necessary for the first process equipment 21a among the cassettes loaded on the stocker 23. To the mounting portion 15 using.

Thereafter, the cassette automatic conveying apparatus in which the cassette 17 is loaded is moved along the line 22 to the first process equipment 21a which requires the cassette 17.

Here, the automatic cassette feeder (AGV) is positioned in front of the first process equipment 21a by reading the mark plate of the first process equipment 21a using the position detection sensor 13. .

Then, the communication sensor 12 is used to communicate with the first process equipment 21a, thereby preparing the cassette 17 loaded on the mounting unit 15 to be loaded into the first process equipment 21a. .

That is, by moving the drive shaft 11b of the robot arm 11 upward, the slide 11a located above the drive shaft 11b is moved upward.

At this time, as the slide 11a rises higher than the mounting portion 15, the cassette 17 loaded on the mounting portion 15 is placed on the slide 11a and the slide 11a. You go up together.

Thereafter, the movement of the drive shaft 11b is stopped, and the slide 11a extends in a step shape toward the first process equipment 21a, thereby moving the cassette 17 to the first process equipment 21a. Will be loaded into.

Subsequently, the cassette automatic conveying apparatus moves again along the line 22 to the stocker 23, and through this process, this time loads the cassette 17 necessary for the second process equipment 21b, and again the line ( 22, the second process equipment 21b is moved to load the cassette 17 into the second process equipment 21b.

The conventional cassette automatic conveying apparatus (AGV) is to repeat the above process, thereby delivering the cassette 17 to each process equipment (21a, 21b).

However, the cassette automatic conveying apparatus and the cassette conveying method according to the prior art as described above had the following problems.

In semiconductor or LCD factories, AGVs are used to move and transfer cassettes stored in substrates.The AGVs use positioning sensors and mark plates to position the cassettes in front of the equipment port. Grab and then move the material of the AGV to the previously entered value and finally transport the cassette to the desired process equipment.

However, if an environmental change such as an AGV position abnormality, a correction value error, or interference with external parts occurs during the transfer of the AGV after the correct position of the AGV, the AGV cannot cope with this, and productivity is lowered due to an alarm and a board breakage. .

That is, since the cassette and the slide of the robot arm are not corrected at the time of unloading of the cassette, when the cassette is not in the correct position, alarms and breakage of the substrate have a great adverse effect on productivity.

The present invention has been made to solve the above-mentioned problems, the cassette to adapt to environmental changes through the consistency check and correction of the position of the cassette and the robot arm to be conveyed to prevent the occurrence of errors due to the cassette position error and substrate damage The object is to provide an automatic conveying apparatus and a cassette conveying method.

The cassette automatic conveying apparatus according to the present invention for achieving the above object is provided with a cassette having a plurality of substrates accommodated and a mark plate on the back, a mounting portion for mounting the cassette, and a lower portion of the mounting portion A robot arm provided with a first positioning sensor for loading a cassette mounted in the process equipment provided in each process step and reading information of the mark plate of the cassette to detect a position, and for supporting the mounting part and the robot arm. A body part, a communication sensor provided on one side of the body part to communicate with an adjacent stalker or process equipment, and a second position detection sensor for sensing that a proximity to a desired position of the stocker or process equipment is provided; Characterized in that it comprises a moving means provided in.

In addition, the cassette conveying method according to the present invention for achieving the above object comprises the steps of transferring a conveying command from the host, the step of moving the cassette to the output port of the stocker according to the conveying command of the host, and the cassette Moving the robot arm of the cassette automatic transfer device downward, reading position information of the mark plate attached to the cassette through the position detection sensor of the robot arm, and detecting a position with the cassette; Comparing the current position of the robot arm with the current position, returning the cassette to the process equipment if the comparison value is identical, and comparing the current position of the robot arm with the current position if the comparison value is inconsistent. Characterized in that it comprises a step of correcting the error.

Hereinafter, with reference to the accompanying drawings, a cassette automatic conveying apparatus and a cassette conveying method according to the present invention will be described in detail.

Figure 4 shows a cassette conveying system according to the present invention, Figure 5 is a side view showing a system showing a cassette automatic conveying apparatus equipped with a cassette in FIG.

As shown in FIG. 4, a control system for controlling a conveying system according to the present invention includes first to fifth hosts 101, 102, 103, 104, and 105.

Here, the first host 101 is the highest host that receives a transfer instruction from the operator to move the cassette 150. When a worker inputs a return command to the first host 101, the first host 101 transmits the return command to the second host 102 and the third host 103.

The second host 102 communicates with the first host 101 and the third host 103 and controls the process equipment 200 to perform any LCD manufacturing process.

The return command sent from the first host 101 to the second host 102 is transmitted to the process equipment 200.

Here, the process equipment 200 is provided with a loader 210 for unloading the cassette 150 conveyed by the cassette automatic conveying apparatus 300, the loader 210 is stored in the cassette 150 A transfer robot (not shown) for supplying a substrate (not shown) to the process equipment 200 one by one is provided.

Meanwhile, the third host 103 communicates with the first host 101 and the second host 102, and controls the fourth host 104 and the fifth host 105.

The return command transmitted from the first host 101 to the third host 103 is transmitted to the fourth host 104 and the fifth host 105.

The fourth host 104 communicates with the third host 103 and controls the operation of the cassette automatic transfer device 300. Of course, the transfer command received by the fourth host 104 is transmitted to the cassette automatic transfer device 300.

The fifth host 105 communicates with the third host 103 and controls a stocker 400 that stores a plurality of cassettes 150 on which a plurality of substrates are mounted.

Of course, the return command received at the fifth host 105 is transmitted to the stocker 400.

Meanwhile, before the stocker 400 supplies the cassettes 150 on which the substrates of which process is completed to other equipment that performs the next process, the substrate processing capability and the processing time of the equipments that perform each process. In order to solve the buffering (buffering) problem caused by the difference of the, is a facility for temporarily storing the cassette 150.

Therefore, the cassettes 150 on which substrates which have been finished in a certain process are mounted are temporarily stored in the stocker 400 and then supplied to other equipment which performs another process.

The stocker 400 performing the above functions includes a stock port 410 on which a cassette 150 on which substrates are completed, and a plurality of shelves storing the cassettes 150. (Not shown), an output port 420 from which the cassette 150 is shipped, and the stocker while moving between the receiving port 410 and the shelf and between the shelf and the delivery port 420. And a stacker robot (not shown) that carries the cassette 150 within 400.

Meanwhile, in order to process the plurality of cassettes 150 without errors as described above, each cassette 150 has unique ID information, and the stocker 400 checks each ID information of each cassette 150. It is then stored on the shelf.

To this end, the receiving port 410 of the stocker 400 is provided with a reader 430 that can check the ID information of the cassette 150.

 In addition, an ID display unit 151 in which ID information of the cassette 150 is recorded is provided on at least one of an upper side and a lower side of the cassette 150.

In addition, a mark plate 152 is attached to the rear center portion of the cassette 150.

In the present invention, as an example of the ID display unit 151 and the mark plate 152, a bar code is presented.

With the above structure, the reader 430 reads the ID display unit 151 so that the stocker 400 can check the ID information of the cassette 150.

In addition, when the cassette 150 is shipped, the storage port of the cassette 150 having the ID information corresponding to the transport information received by the stocker 400 is confirmed, and then the delivery port 420 is released from the shelf using the stacker robot. The cassette 150 is transported.

Meanwhile, a reader capable of reading the ID display unit 151 of the cassette 150 is also provided in the loader 210 of the process equipment 200.

Therefore, the loader 210 determines the authenticity of the cassette 150 supplied to the loader 210 by using the reader 201, and then causes the transfer robot to supply the substrate to the equipment 200 one by one. do.

On the other hand, the cassette automatic conveying apparatus 300, under the control of the fourth host 104, the cassette 150 from the process equipment 200 to the receiving port 410 of the stocker 400, and The stock port 420 of the stocker 400 returns to another process equipment 200.

Here, the fourth host 104 controls at least one or more cassette automatic conveying apparatuses 300, and each cassette automatic conveying apparatus 300 is provided with a cassette automatic conveying apparatus according to an instruction of the fourth host 104. The conveying apparatus control part which controls each component of the 300 is provided.

As shown in FIG. 5, the cassette automatic conveying apparatus 300 is provided on a driving unit 310 that runs a predetermined section under the control of the conveying apparatus controller, and on one side of the traveling unit 310, for example, an upper portion thereof. And the mounting unit 320 on which the cassette 150 is placed.

Here, a plurality of wheels 311 driven by the driving motor is provided at the lower end of the driving unit 310.

In addition, the mounting unit 320 is provided with a guide block 321 for guiding the cassette 150 to be accurately mounted and fixing the mounted cassette 150 so as not to move when the traveling unit 310 is moved. do.

Meanwhile, the cassette automatic transfer device 300 further includes a robot arm 330 for loading the cassette 150 into the mounting unit 320 or unloading from the mounting unit 320. do.

Here, the robot arm 330 is mounted on the upper portion of the running portion 310 and the main shaft 331 that can move or rotate in the vertical direction, and mounted on the main shaft 331 can be stretched in the horizontal direction A slider 335, and a plurality of first position detection sensors 337 for detecting the position by reading the mark plate 152 of the cassette 150 at regular intervals within the surface of the slider 335; It is configured.

When the robot arm 330 is provided in the cassette automatic conveying apparatus 300 as described above, the cassette automatic conveying apparatus 300 is the process equipment 200 and the receiving port 410 and the delivery port of the stocker 400. The cassette 150 in 420 may be directly loaded onto the mounting unit 320, or the cassette 150 loaded on the mounting unit 320 may be unloaded onto the equipment 200 and the stocker 400. .

On the other hand, when the cassette automatic conveying device 300 is to convey the cassette 150, the stocking port 410 and the delivery port 420 of the stocker 400, or should be able to be located exactly in front of the process equipment 200 do.

To this end, the cassette automatic conveying apparatus 300 is provided with a second position detection sensor 340, and the loader 210 and the stocker 400 of the process equipment 200 is provided with a mark plate 250.

Here, the second position detection sensor 340 reads the mark plate to help the cassette automatic conveying apparatus 300 to be accurately positioned in front of the loader 210 or the stocker 400 of the process equipment 200.

In addition, the cassette automatic conveying apparatus 300 accurately positioned in front of the loader 210 or the stocker 400 of the process equipment 200 may smoothly and accurately load or unload the cassette 150. Or be able to communicate with the stocker 400.

To this end, the cassette automatic conveying device 300 is further provided with a communication sensor 350 to communicate with the process equipment 200 or the stocker 400 to help the correct loading or unloading operation.

On the other hand, when the cassette 150 is supplied to the loader 210 of the equipment 200 by the cassette automatic transfer device 300, the transfer robot provided in the loader 210 is stored in the cassette 150. The substrates are taken out one by one and then supplied to the stage of the process equipment 200.

Figure 6a is a perspective view showing a cassette transported through a cassette automatic transport apparatus according to the present invention, Figure 6b is a rear view showing the cassette back of Figure 6a.

As shown in FIG. 6A, a side that is installed between the first side edges 155 and 156 and the second side edges 157 and 158 of the upper plate 153 and the lower plate 154 to support the upper plate 153 and the lower plate 154. A stopper 162 installed between the plates 159 and the third side surfaces 160 and 161 of the upper plate 153 and the lower plate 154 to support the upper plate 153 and the lower plate 154 to face each other. A plurality of first shelves 163 formed on one side of the side plate 159 in a direction and a plurality of second shelves formed on one side of the stopper 162 in a direction orthogonal to the first shelves 163. Shelves 164 are provided.

Here, eight side plates 159 are installed between the upper plate 153 and the lower plate 154. That is, four side plates 159 are installed between the first side edges 155 and 156, and four side plates 159 are installed between the second side edges 157 and 158. The first shelves 163 formed on one side of the side plates 159 are regularly arranged at predetermined intervals to provide a loading space of the substrate. The first shelves 163 constantly arrange the substrate loaded in the cassette. Two stoppers 162 are installed between the third side edges 160 and 161.

In addition, the stoppers 162 uniformly align the substrates while stopping the substrate supplied from the conveyor. The second shelves 164 formed on one side of the stoppers 162 support the substrate loaded in the cassette and minimize the impact of the substrate supplied from the conveyor.

Meanwhile, the side plate 159 and the stopper 162 of the cassette are formed by attaching PEI (Polyether Imide) on aluminum (Al). Such PEI has high physical strength and low coefficient of friction.

In addition, as shown in FIG. 6B, a first mark plate 152a attached in one direction and a second mark plate intersecting in a direction perpendicular to the first mark plate 152a are attached to the rear center portion of the lower plate 154 of the cassette. 152b is attached.

Here, the first and second mark plates 152a and 152b are used to unload the cassette 150 from the stopper 400 using the robot arm 330 of the cassette automatic transfer device 300. A portion that is read through the plurality of first position detection sensors 337 configured at 330 is composed of a barcode.

Fig. 7A is a plan view showing a slide of the robot arm of the cassette automatic transfer device according to the present invention, and Fig. 7B is a configuration diagram showing a position detection sensor attached to the slide of Fig. 7A.

As shown in FIG. 7A, four position detection sensors 337 are attached to the surface of the slide 335 at regular intervals.

The position detecting sensor 337 is configured as shown in FIG. 7B to lower the cassette 150 loaded on the stocker 400 when the cassette 150 is loaded into the processing equipment 200 through the robot arm 330. The slide 335 is inserted to read the information of the first mark plate 152a and the second mark plate 152b formed on the rear surface of the cassette 150 to detect the position of the cassette 150.

On the other hand, the position detection sensor 337 is vertically mounted on the upper surface of the slide 335 so that the four image sensors (top) to the upper surface, the first, second mark on the back surface of the cassette 150, that is, the lower surface The plate is mounted vertically.

 Figure 8a is a view for explaining the problem caused by the position shift when unloading the cassette by the robot arm in the cassette automatic transfer device according to the prior art, Figure 8b is a cassette by the robot arm in the cassette automatic transfer device according to the present invention It is a figure for explaining the position correction method at the time of unloading.

As shown in Fig. 8A, conventionally, the unloading process is not carried out without knowing the exact position of the cassette 17 when the cassette is mounted to the mounting portion of the stocker 23 or when the slide 11a is inserted into the lower portion of the cassette 17. Is executed.

Therefore, an alarm occurs and the substrate breakage in the cassette occurs during unloading.

In contrast, in the present invention, as shown in FIG. 8B, when the slide 335 of the robot arm moves to the lower surface of the cassette 150 to perform unloading, four position detection sensors 337 configured in the slide 335 are provided. Reads the information of the first and second mark plates 152a and 152b attached to the lower surface of the cassette 150 to obtain position information, and if the slide 335 is out of position, the position correction is performed. To ensure correct unloading.

On the other hand, the operation of the cassette transport system according to the present invention having the configuration as described above in more detail as follows.

9 is a flowchart for explaining a cassette conveying method according to the present invention.

First, the operator checks the ID of the cassette 150 to be returned and then inputs the return information to the first host 101. Then, the conveyance command given to the first host 101 is transmitted to the process equipment 200 through the second host 102, and the cassette automatic through the third host 103 and the fourth host 104. The transfer device 300 is transferred to the stocker 400 through the third host 103 and the fifth host 105 (S110).

Subsequently, the stacker robot of the stocker 400 which has received the transfer command finds the cassette 150 having the corresponding ID on the shelf and moves the cassette 150 to the output port 420 (S120).

In addition, the cassette automatic conveying apparatus 300 which has received the conveying instruction moves to the stocker 400 and then reads the information of the mark plate attached to the stocker 400 through the second position detecting sensor 340 and fixes the sheet. Stop in position. Then, the slide 335 of the robot arm 330 is moved to the lower portion of the cassette 150 (S130).

Subsequently, the first and second mark plates 152a and 152b formed on the rear surface of the cassette 150 using four first position detection sensors 337 configured on the slide 335 of the robot arm 330. The position of the cassette 150 is checked by reading the information (S140).

Subsequently, it is determined whether the current position of the slide 335 has reached the correct position through the slide 335 moved to the lower surface of the cassette 150 (S150).

If an error occurs between the current position of the slide 335 and the correct position, the error is calculated and the position of the slide 335 is corrected by correcting the x, y, θ values (S160).

In addition, when the current position of the slide 335 reaches the home position, the slide 335 loads the cassette 150 to the mounting unit 320 and conveys it to the process equipment 200 (S170).

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

The cassette automatic conveying apparatus and the cassette conveying method according to the present invention as described above have the following effects.

In other words, before loading the cassette by using the slide of the robot arm, the position detection sensor configured on the slide and the mark plate mounted on the cassette detect and correct an error between the current position and the correct position of the slide, thereby causing it to occur during the conveying process. It is possible to prevent breakage of the substrate inside the cassette due to the occurrence of an alarm and an impact.

1 is an exploded perspective view showing a part of a general liquid crystal display panel

Figure 2 is a front view showing a cassette automatic conveying apparatus according to the prior art

3 is a plan view of a process line for explaining a cassette conveying process of a cassette automatic conveying apparatus according to the prior art;

4 is a cassette conveying system according to the present invention.

5 is a side view showing a system showing a cassette automatic conveying apparatus equipped with a cassette in FIG.

Figure 6a is a perspective view showing a cassette transported through a cassette automatic transport apparatus according to the present invention

FIG. 6B is a rear view of the cassette rear of FIG. 6A;

7A is a plan view showing a slide of the robot arm of the cassette automatic conveying apparatus according to the present invention.

FIG. 7B is a block diagram showing a position detection sensor attached to the slide of FIG. 7A

8A is a view for explaining a problem caused by position shift when unloading a cassette by a robot arm in a cassette automatic transfer device according to the related art.

8B is a view for explaining a position correction method during cassette unloading by a robot arm in the cassette automatic conveying apparatus according to the present invention.

9 is a flowchart illustrating a cassette conveying method according to the present invention.

Explanation of symbols for the main parts of the drawings

150: cassettes 152a, 152b: first and second mark plates

300: automatic cassette feeder 330: robot arm

335 slide 337: first position detection sensor

340: second position detection sensor

Claims (7)

A cassette in which a plurality of substrates are stored and a mark plate is attached to the back, A mounting portion for mounting the cassette; A robot arm provided at a lower portion of the mounting portion and equipped with a first positioning sensor for loading a cassette mounted on the mounting portion into the process equipment provided in each process step and reading the information of the mark plate of the cassette to detect a position; A body part for supporting the mounting part and the robot arm, A communication sensor for communicating with an adjacent stalker or process equipment provided on one side of the body portion, and a second position detecting sensor for sensing that a proximity to a desired position of the stocker or process equipment is provided; Automatic cassette delivery device characterized in that it comprises a moving means provided in the lower portion of the body portion. The cassette automatic conveying apparatus according to claim 1, wherein the mark plate comprises a bar code. 2. The cassette automatic conveying apparatus according to claim 1, wherein the mark plate is composed of two mark plates that intersect in a direction perpendicular to each other at a central portion of the rear surface of the cassette. The cassette automatic conveying apparatus according to claim 1, wherein the first position detecting sensor is configured on a slide of the robot arm. 5. The cassette automatic conveying apparatus according to claim 4, wherein the first position detection sensor is vertically configured such that four image sensors face upward on a slide. The cassette automatic conveying apparatus according to claim 1, wherein the mark plate is vertically configured to face the bottom surface of the cassette. Delivering a return command from the host; Moving the cassette to an output port of the stocker according to the return instruction of the host; Moving the robot arm of the cassette automatic conveying apparatus under the cassette; Detecting position with the cassette by reading position information of a mark plate attached to the cassette through a position detection sensor of the robot arm; Comparing the current position of the robot arm with a home position value; Returning the cassette to process equipment when the compared values match; And correcting an error between the current position and the correct position of the robot arm when the compared values are inconsistent.