JPS63169255A - Carrier transferring method for automatic pallet exchanger - Google Patents

Abstract

PURPOSE:To position a carrier, by stopping a servomotor after drawing the carrier at a smaller speed in a coating distance where the carrier goes forward by inertial force along, than allowable slippage to a pallet exchange position at a time when the carrier comes nearer to this pallet exchange position. CONSTITUTION:During crawling rotation, backlash in a driving system is put aside to one direction, coming into a backlash eliminated state. Afterward, if rotational output to a servomotor 5 is stopped, inertial force to make a carrier 4 go forward and running resistance force to make it stop both act on the carrier 4. At this time, rotational frequency in the servomotor 5 just before stoppage is decelerated to the extent that a coasting distance where the carrier 4 is advanced by inertial force becomes smaller than allowable slippage to a pallet exchange position C, so that after stopping the rotational output to the servomotor, the carrier 4 is stoppage at the specified accuracy. Therefore, total rotational frequency and speed of the servomotor 5 is controlled whereby the carrier 4 can be positioned at the said exchange position C at the specified accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pallet to a machine tool such as a machining center by pulling a carrier for supporting a pallet for supporting a workpiece with an endless chain arranged in a loop shape. The present invention relates to a carrier transfer method of an automatic pallet exchange device for transporting carriers to an exchange position, and more specifically, to a method of stopping a carrier at a pallet exchange position with a predetermined accuracy only by controlling the rotation of a servo motor that drives an endless chain.

[Prior art and its problems]

Automatic pallet exchange equipment uses an endless chain arranged in a loop to transport a pallet loading carrier to a pallet exchange position on a machine tool such as a machining center. Therefore, it is necessary to easily transport and position the carrier.

In conventional automatic pallet exchange equipment, an oil motor is used as the drive motor for the endless chain.
Furthermore, a movable stopper is provided at the pallet exchange position to accurately stop the carrier at the pallet exchange position. This movable stopper retreats from the carrier transfer trajectory when the carrier starts to be transferred, and when the designated carrier approaches the pallet exchange position, moves forward to a position where it can come into contact with the carrier or the pallet on the carrier, and moves the carrier onto the pallet. Stop at the replacement position.

The above-described conventional automatic pallet changing device has the disadvantage that the control becomes complicated because it is necessary to control the operation of the movable stopper in addition to controlling the rotational drive of the oil motor.

As a method for transporting and positioning carriers, a method can be considered in which a servo motor is used as a drive motor for an endless chain, and the total number of rotations thereof is controlled to directly position a designated carrier at a pallet exchange position. However, since a drive system using a chain is composed of mechanical parts having a large balaclabranch, the stopping error due to backlash within the drive system becomes incomparably larger than the stopping accuracy of a servo motor. For this reason, a carrier transfer method using an oil motor and a movable stopper is still used today because the carrier transfer method using total rotational speed control of a servo motor does not allow the carrier to be positioned with a predetermined accuracy.

Therefore, an object of the present invention is to provide a carrier transfer method for an automatic pallet exchange device that uses a servo motor as the drive motor of an endless chain to easily position the carrier directly and with a predetermined accuracy. do.

[Means for solving problems]

The present invention provides an endless carrier transfer method for an automatic pallet exchange device in which a carrier for supporting a pallet for supporting a workpiece is pulled by an endless chain disposed in a loop shape and transferred to a pallet exchange position for a machine tool. A servo motor controlled according to a preset program is used as the chain traction drive source, and when the carrier approaches the pallet exchange position, the coasting distance traveled by the carrier only by inertia is the allowable deviation from the pallet exchange position. To provide a carrier transfer method for an automatic pallet exchange device, characterized in that the rotation of a servo motor is stopped after the carrier is pulled at a speed lower than that of the carrier.

[For production]

In the carrier transfer method of an automatic pallet exchange device according to the present invention, when the carrier approaches the pallet exchange position, the carrier moves at a speed such that the coasting distance traveled by the carrier only by inertia is smaller than the allowable deviation amount with respect to the pallet exchange position. The servo motor is rotated at extremely low speed to pull the

During ultra-low speed rotation, backlash within the drive system is pushed to one direction, resulting in a backlash elimination state.

After that, when the rotational output to the servo motor is stopped, an inertial force that tries to move it forward and a running resistance force that tries to stop it act on the carrier, but the rotational speed of the servo motor just before it stops is Since the carrier is decelerated to the extent that the coasting distance traveled by the inertia force is smaller than the allowable deviation amount with respect to the pallet exchange position, the carrier can be stopped with a predetermined accuracy after the rotational output to the servo motor is stopped. Therefore, by controlling the total number of rotations and speed of the servo motor, the carrier can be positioned at the pallet exchange position with a predetermined accuracy without using a positioning means such as a stopper.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows the mechanical structure of an automatic pallet exchange device to which the method of the present invention is applied. Referring to the figure, an endless chain 3 stretched in a loop between two guide wheels 1°2 has a plurality of carriers 4 arranged at equal pitches for carrying pallets for supporting workpieces (not shown). are installed separately. The rotational driving force of the servo motor 5 is transmitted to the chain 3 via a reduction gear 6 and a drive wheel 7. Although a DC servo motor can be used as the servo motor 5, an AC servo motor that does not require maintenance such as brush replacement is preferable. Driven by the servo motor 5, the chain 3 moves along the loop trajectory, thereby transporting the carrier 4 along the loop trajectory. A pallet exchange position C of an automatic pallet exchange device with respect to a table 8 of a machine tool such as a machining center is set in advance. At the pallet exchange position C, pallets are transferred between the carrier 4 and the table 8 of the machine tool.

The rotation of the servo motor 5 is controlled by the control device shown in FIG. 2 according to the flow shown in FIG. 3.

In FIG. 2, 20 is a well-known microprosefna,
Basically CPU21. It is composed of a ROM 22 and a RAM 23. A program for controlling the CPU 21 is written in the ROM 22 . The RAM 23 stores the total number of carriers, the total amount of bank crash in the power transmission system, signal pattern data, etc. input from the input device 24 through the I/○ interface 25, and also stores the carrier number of carrier 4 specified last time. is memorized.

When the machining of the workpiece by the machine tool is completed, the pallet on the table 8 of the machine tool is transferred onto the carrier (previously specified carrier) 4 waiting at the pallet exchange position C, and then transferred to the next specified other carrier. The carrier 4 is transferred to the pallet exchange position C.

This transfer is performed as follows.

When the carrier number of the carrier 4 to be transported to the pallet exchange position C this time is specified using the input device 24, the carrier number is stored in the RAM through the I10 interface 25.
23. Next, when a rotation command is input through the input device 21, the CPU 21 reads out the previously specified carrier number, the total number of carriers, and the currently specified carrier number from the RAM 23 according to the processing program stored in the ROM 22, and stores these. Process for determining the rotational direction of the servo motor 5 for shortcut control of the carrier 4 to the pallet exchange position C based on the data, that is, the carrier 4
Set the transfer direction clockwise (CW) or counterclockwise (C
CW), and a rotation direction command as a result of the processing is given to the output device 26 through the 110 interface 25 (step 41 in FIG. 3).

Next, the CPU 21 calculates the basic movement distance for transporting the currently designated carrier 4 to the pallet exchange position C according to the processing program stored in the ROM 22. Compare whether the rotation direction is the same as the previous rotation direction read from the RAM 23 (step 43 in FIG. 3). If the rotation direction is the same, the basic movement amount is set as the actual movement it (number of pulses) PT. Write to RAM 23 (step 45 in FIG. 3),
If the rotation directions are different, read out the correction amount corresponding to the amount of backlash for the entire drive diameter inputted in advance from the input device 24 and stored in the RAM 23 (step 44 in FIG. 3), and this correction amount - is added to the basic movement amount to calculate the actual movement amount (number of pulses) PT, which is written into the RAM 23 (step 45 in FIG. 3).

Next, the CPU 21 selects, for example, a variable parameter of the signal pattern corresponding to the speed diagram A shown in FIG.
2 (step 46 in FIG. 3). This calculation is performed, for example, as follows.

Pl: Number of pulses corresponding to the distance (1/3 of one carrier pitch) of the acceleration section (C, ~C2) P3: Deceleration section (
Number of pulses corresponding to the distance of C2 to C3 (carrier l pitch 1/3) 4: Number of pulses PT corresponding to the distance of the low speed section (Ca to CS) (10 times the backlash amount of the power transmission system): The number of pulses P, , P, , p, calculated as the actual amount of movement, is stored in the RAM 23 in advance. Therefore, the number of pulses P2 is calculated by the following formula: p2=p'r-p, -p3-p4. The calculated pulse number P2 is stored in RAM2.
3 is stored.

Next, the CPU 21 provides a drive output signal to the output device 26 through the I10 interface 25 in accordance with the signal pattern stored in the RAM 23 (step 47 in FIG. 3). As a result, the servo motor (M) 5 rotates in the specified direction, and its speed is controlled according to the speed diagram A shown in FIG.

Therefore, the carrier 4 is accelerated in the section (01-Cz), transferred at a constant high speed in the section (C2-C3), decelerated in the section (C3-Ca), and transferred at a very low speed in the section (04-C5). Ru.

The rotation of the servo motor 5 is detected by the encoder 27, and the total number of rotations is compared with the number of pulses PT of the actual movement amount (step 48 in FIG. 3). When the total rotational speed detected by the encoder 27 reaches the pulse number PT, the output from the output device 26 to the servo motor 5 is stopped, and the movement of the carrier 4 is also stopped (step 49 in FIG. 3).

The rotational speed of the servo motor 5 in the section (CaNO3) is such that even if the carrier 4 tries to move further due to the inertia of the driven system after the output to the servo motor 5 is stopped, it does not move forward at all due to the action of running resistance, or even if it moves forward, The speed is set in advance at such a speed that the coasting distance δ can be within the permissible value for positioning (for example, 172, which is a value that does not interfere with pallet exchange).

The speed in the very low speed section (C4 to Cs) can be freely adjusted through the input device 24. This adjustment was made by actually trial running the automatic pallet changing device several times, and
This is done while always checking whether or not the valet replacement position C is within the allowable range.

Therefore, in the very low speed section (Ca to CS), the entire drive system is kept under tension. That is, the section of the chain 3 between the drive wheel 7 and the designated carrier 4 is in a tensioned state, and the engagement state between the teeth 7a of the drive wheel 7 and the roller 3a of the chain 3 is also in the state shown in FIG. Thus, the front end of the tooth 7a and the rear end of the roller 3a in the rotation direction F of the drive wheel 7 are maintained in contact. Therefore, the distance between the chain wheel and the designated carrier 4 is not affected by backlash in the drive system or slack in the chain 3.

When the rotational output to the servo motor 5 is stopped, an inertial force that tries to move the carrier 4 forward and a running resistance force that tries to stop it act on the carrier 4, but the rotational speed of the servo motor 5 just before it stops is As described above, the carrier 4 is decelerated to such an extent that the coasting distance δ traveled by the carrier 4 due to inertia force is smaller than the allowable deviation amount with respect to the pallet exchange position IC. can be stopped with a predetermined accuracy. Therefore, by controlling the total number of rotations of the servo motor 5 required to transport the carrier 4 to the pallet exchange position C, the carrier 4 can be moved to a predetermined position only by controlling the servo motor 5 without using positioning means such as a stopper. It becomes possible to position the pallet at the pallet exchange position C with an accuracy of .

In addition, in the example shown in FIG. 4, the ultra-low speed section (C4 to CS)
The rotational speed of the servo motor 5 is set to be a constant speed, but the embodiment is not limited to this. For example, as shown in FIG.
Ca-C4') is set at a constant speed, and the rear section (04'-C5
), the speed may be gradually reduced so that the speed is always higher than the coasting speed of the carrier 4 (indicated by the broken line B in the figure). Furthermore, as shown in FIG. 7, even if the speed is gradually decelerated so that the speed is always higher than the coasting speed of the carrier 4 (indicated by vAB in the figure) in the ultra-low speed section (Ca to CS), good. Furthermore, various changes can be made to the number of carriers, the arrangement structure of the drive system, etc. as necessary.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the rotational speed of the servo motor immediately before the carrier stops is decelerated to such an extent that the coasting distance traveled by the carrier due to inertia is smaller than the allowable deviation amount with respect to the pallet exchange position. Therefore, the carrier can be stopped with a predetermined accuracy after the rotational output to the servo motor is stopped. Therefore, by controlling the total number of rotations and rotational speed of the servo motor, it becomes possible to position the carrier at the pallet exchange position with a predetermined accuracy without using positioning means such as a stopper, making it easy and highly accurate. This means that it is possible to realize the control of

Furthermore, since a movable stopper mechanism or the like is not required, the mechanical drive system is simplified. Furthermore, since a servo motor is used instead of an oil motor, maintenance of the drive system such as the motor is not required, and the surrounding environment can be prevented from becoming contaminated, making it possible to improve control responsiveness and reliability. Many effects can be obtained, such as increasing the carrier transport speed.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a mechanical drive system of an automatic pallet changing device to which the present invention is applied, FIG. 2 is a schematic block diagram of a control device for carrying out the method of the present invention, and FIG. Figure 4 shows the flow of processing by the control device shown in Figure 4. A speed diagram showing an example of IIILQ, FIG. 5 is an enlarged sectional view of the main part showing the state of engagement between the drive wheel and chain during carrier transfer, and FIGS. 6 and 7 respectively show the servo motor according to the present invention. FIG. 7 is a speed diagram showing a modification of the control mode. In the figure, 3 is an endless chain, 4 is a carrier, 5 is a servo motor, and C is a pallet exchange position. Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] 1. Carrier transfer of an automatic pallet exchange device in which a carrier for supporting a pallet for supporting a workpiece is pulled by an endless chain arranged in a loop and is transferred to a pallet exchange position for a machine tool. In this method, a servo motor controlled according to a preset program is used as the traction drive source of the endless chain, and when the carrier approaches the pallet exchange position, the coasting distance traveled by the carrier only by inertia force is the pallet exchange position. 1. A carrier transfer method for an automatic pallet exchange device, characterized in that the rotation of a servo motor is stopped after the carrier is pulled at a speed that is smaller than an allowable deviation amount for the carrier. 2. Claim No. 2, characterized in that when the direction in which the carrier is transported toward the pallet exchange position is opposite to the previous transport direction, the servo motor is rotated extra by an amount corresponding to the amount of backlash within the drive system. A carrier transfer method for an automatic pallet exchange device according to item 1.