JPS6195847A - Pallet changer - Google Patents

Abstract

PURPOSE:To obtain compact device by disposing drive sources for taking in and out of pallets concentratedly on a base side and making drive sources disposed on the base side small reciprocating moving type. CONSTITUTION:When machining of a work of a pallet 19A is placed on a machine table is completed, the machine table moves to a pallet replacing position and a cylinder 32 works simultaneously to forward a taking in-and-out table 22. next, engaging action of a hook 41 and a notch 38 of the pallet 19A is completed, and the taking in-and-out table 22 is retired to the back direction with the pallet 19A. Next a motor 14 works to rotate a table 6 and a pallet 19B is indexed to the left side pallet taking in and out position, and the pallet 19A already machined is indexed to the right side pallet taking in and out position. Then, the pallet 19B is clamped to the machine table and entered in machining operation, and a work already machined on the pallet 19A is replaced with a new work.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called rotary table-type pallet changer that is used for loading and unloading pallets onto and from the work table of a machine tool, and particularly relates to a pallet changer that is used to load and unload pallets onto and from a work table of a machine tool. This relates to a pallet changer that does not have any driving sources for loading and unloading, and all driving sources are centrally arranged on the base side.

The conventional rotary table type pallet changer is
Most of them have a drive source for loading and unloading pallets on a table that can be rotated completely on the pace. This conventional method is simple in concept, but the hydraulic and electrical wiring for all operations of the drive unit for loading and unloading pallets is rotated from the fixed pace side via rotary pulp, slip rings, or flexible tubes. It is necessary to connect to the table side, which requires a complicated and expensive connection structure, and is a major cause of machine failure.

In addition, as an example of installing a drive source for loading and unloading pallets on the pace side, the feed screw on the table is rotated from the rotation drive source on the base side via a pair of bevel gears provided at the center of table rotation. Because it is a screw-screw drive system, there is a limit to the loading and unloading speed, and the structure has no choice but to move not only the pallet at the unloader's position, but also the pallet on the opposite side (the pallet at the work loading/unloading position) at the same time. This not only requires a large amount of power from the drive source, but also has problems such as slow setup time.

The present invention solves the problems of the conventional rotary table type pallet changer described above, and converts the reciprocating movement with a small stroke on the pace side into the reciprocating movement of the loading/unloading table, and the loading/unloading table is used to perform barre-to-load operations. It is designed so that it can be carried in and out.

That is, a guide rail that is located between the table that rotates and indexes on the pace and the top surface of the pace and extends in the radial direction corresponding to the diameter of the base, and two conveyor rails that are located inside the guide rail of the carriage and are provided in parallel. A guide rail for entering the platform,
Only the loading/unloading table with all the racks sliding on this guide rail and engaging the gears of the carriage from both sides, and the loading/unloading table indexed for loading/unloading pallets are released from the table. When the pallet is loaded or unloaded, the gear of the carriage rotates from engagement with the rack of the stationary loading/unloading table as the carriage moves. The rotation of this gear moves the rack of the movable loading/unloading platform forward, so
The movement of the loading/unloading table is twice as long as the movement of the carriage.

In the present invention, by completely interposing the amplification and combination means between the reciprocating drive source and the loading/unloading table, only the reciprocating part with a narrow stroke and the reciprocating source are required, and the overall speed is improved. It is compact (Ig). Also, unlike the method of loading and unloading the loading/unloading table with a screw or a lever, the reciprocating motion of the reciprocating drive source is amplified and transmitted to the loading/unloading table, so the loading/unloading speed can be increased. .

Furthermore, only the pallet that is indexed to the carry-out person's position can be carried in and out, and when the pallet is in the angle recording position of the song, the table ( b) It prevents the pallet from flying out due to centrifugal force during busy periods.Also, since only one pallet at the carry-out person's position is moved by the reciprocating drive source, there is an advantage that the output of the reciprocating noise source can be small. .

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a pallet checker/shaper according to the present invention will be described in detail below with reference to all the drawings.

1 to 7 are first examples of the pallet changer of the present invention. This is an embodiment in which all levers are used as the increased IM transmission means, and two pallets can be loaded and unloaded using one loading/unloading table. Figures 1 to 6
As shown in Figures (A) and (B), a sub-base 2 with a circular upper surface is provided on the pace 1 with the pole standing upright.

A table 6 having six rows 7-5A to 5F that fully rolls on the upper surface is placed on the upper surface of the sub-pace 2, and a substantially fan-shaped pucket 7 bolted to the upper surface of the table 6 is shown in FIG. As shown in FIG. 2, the table 6 is rotatably supported on the support column 4 by a bearing 8, so that the table 6 can rotate on the subspace 2 with the entire center of the support column 4 being the center. Does the nut 9 and cover 10 in Figure 5 prevent the bearing 8 from being removed? Let's do it.

A cylindrical portion 1 surrounding the sub-base 2 is provided on the outer periphery of the table 6.
1 is formed, and a large diameter gear 12 is formed on the lower outer periphery of the cylindrical portion 11. As shown in FIG. 1, an L-shaped stay 16 is bolted to the side surface of the pace 1, and a motor 14 is attached to the stay 16 facing upward.

A small gear 15 keyed to the output shaft 14A of the motor 14
is engaged with the large gear 12 of the table 6 to rotate the table 6 clockwise and counterclockwise.

As shown in FIGS. 2, 6, and 7, two guide rails 16A and 16B each having an L-shaped cross section are attached to the upper surface of the table 6 in the radial direction. . A plurality of guide rails 1 (5A, 1 (SB1C: vertical guide row)-17 and horizontal guide rollers 18 are attached to guide the loading and unloading of pallets 19A, 19B.

As shown in FIG. 1 and FIG. 6(A), the sub-base 2 is integrated with two parallel guide rails 20A and 20B having the same length as the diameter of the sub-base 2 in the diametrical direction of the sub-base 2. It is formed as follows. Guide grooves 21A, 21B are formed on the upper surface of the guide rails 2OA, 20B over the entire length thereof, and the guide grooves 21A, 21BK are connected to the loading/unloading table 22.
Guided by rollers 23A and 25B mounted on both sides, the loading/unloading table 22 can reciprocate in the diametrical direction along the guide 421A121B. Further, the left and right rollers 23A, 23B are guided at their upper sides by guide plates 24A, 24B having the same length as the diameter of the sub-base 2.

The table 6 has a loading/unloading platform 2 over its entire diameter.
The loading/unloading table 22 shown in FIG. 1 and FIG.
A circular hole 26 is formed in the center of the table 6 so that the table 6 can be rotated and indexed without interfering with the loading/unloading table 22 when the table 6 is in the most retracted state.

As shown in FIGS. 1 and 6(A), the lower end protrusion 22AK of the loading/unloading table 22 has the upper end of the lever 27 pivoted by a pin 28. There is a pin 29 on the bottom of Pace 1.
A bracket 50 on which is implanted is bolted, and the long groove 27 pin AIC pin 29 at the lower end of the lever 27 is slidably fitted therein. Further, a cylinder (reciprocating drive source) 62 is pivotally supported by a stay 61 attached to the side surface of the pace 1 by a pin 33. A U-shaped bracket 64 that inserts the lever 27 is screwed to the tip of the piston/rod 32A that protrudes from the cylinder 62, and the bracket 34 is pivotally attached to the intermediate portion of the lever 27 by a pin 35. Therefore, when the piston rod 32A'i is reciprocated, the loading/unloading table 22 moves by a distance twice as large as that of the piston rod 62A.
K? 9 Sliding back and forth.

4 to 7 (as shown, a protrusion 22B that protrudes upward from a circular hole 26 at the center of the table 6 is formed at the tip of the four-purpose access table 22. The upper surface of the protrusion 22B A block 66 is bolted to the protrusion 22.
A notch 68 is vertically slidably inserted into the hole 67 drilled in B, and is biased upward by a spring 39. The upward removal of the notch 68 is prevented by a pin/40 hammered into the side of the protrusion m22B.

In addition, there is a hook-shaped 7 on the side of pants) 19A and 19B.
Tug 41 is bolted. On the front surfaces of the hook 41 and the notch 38, engaging surfaces 41B and 38B are formed which are perpendicular to the inclined surfaces 41A and 58A. Therefore, as shown by the two-dot chain line "f' in Figure m1, when the loading/unloading table 22 moves forward to pick up the pants) 19At = the slope 38A of the notch 68 and the hook 41. Slope 4
1A makes contact, the notch 38 is retracted, and the loading/unloading platform 22
The engagement surface 41B of the 7th claw 41 and the notch 68 at the MiJ leading end of
, 38B are engaged.

In addition, on the sides of the seven hooks 41 and the notches 38, there are inclined surfaces 41C.
and 380 are formed. This is the place where I decided to replace the pant l-19A pallet on the machine table.
This is to reduce the time loss caused by moving the loading/unloading table 22 forward after confirmation. That is,
In the present invention, the pallet is advanced to the pallet exchange position shown by two points 4N in the figure. Therefore, when the loading/unloading table 22 and the panties 19A reach the pallet exchange position almost simultaneously, the slope 41C on the side of the hook 41 and the slope 3 on the side of the notch 68
Due to the combined effect of the contact with the notch 8C and the contact with the front inclined surfaces 41A and 38A, if the six notches 22 reach the pallet exchange position first, the hook 41 will be able to remove the notch 68 without fully pushing it. An engaging operation is performed.

As shown in FIGS. 4 and 5, a disk (locking means) 42 is bolted to the north end of the support column 4, and an annular groove 43 is formed in the lower surface of the disk 42.

In addition, a width of the hook 41 is provided on the lower surface of the disk 42 to allow the hook 41 to fully enter and exit at the position of the person carrying out the pallet.
Notches 44 are formed at the locations. Also hook 41
An arcuate groove 45 is formed on the upper surface of the disc 42 to match the curvature of the outer circumference of the disk 42 and the outer circumference of the annular groove 4 . Therefore,
When the table 6 rotates from the state shown in Fig. 5, the pallet 1
Since the seven hooks 41 of 9A are rotated along the annular groove 43 after the notches 58 are disengaged, the Q pallet is prevented from popping out while the table 6 is rotating. The called table 6 is 180
When the pallet 19B is rotated once, the pallet 19B on the opposite side is indexed to the pallet loading/unloading position, and the hook 41 of the pallet 19B engages with the notch 38 to become a paddle that can be taken out. When the table 6 is rotated, the hook 41 from the notch 38
In order to facilitate the disengagement and engagement of the hook 41, the vertical engagement surface 411Nd of the hook 41 is inclined from the center to both sides as shown by the broken line in FIG. 6, and the engagement surface 38Bk of the notch 38 is
It makes it easy to attract people.

The first embodiment of the pallet changer of the present invention is constructed as described above and operates as follows. In the initial state, as shown in FIG. 1, the loading/unloading table 22 is at the rear end, the left guide rail 16A is empty, and the right guide rail 16B has a workpiece to be used next attached to it (pants) 19B. is placed.

When processing of the workpiece (pants) 19A placed on the machine table is completed, the machine table moves to the pallet exchange position, and at the same time, the cylinder 32 is actuated to advance the loading/unloading table 22. When the machine table and loading/unloading table 22 both reach the pallet exchange position, the hook 4 of the pallet 19A
1 and the notch 38 are completed, and the limit switches LS-1 and LS-2 are turned on. In response to this confirmation signal, the cylinder 32 is operated in the reverse direction, and the loading/unloading table 22 is retreated to the rearward end along with the pallet 19A. This state is shown in FIG. 5, and the limit switch LS-3 is turned on.

Next, the motor 4 is activated to rotate the table 6 180 degrees counterclockwise as viewed in the plan view of FIG. Therefore, the panties 19B to be used next are assigned to the pallet unloader on the left, and the processed pallet 19A is assigned to the right for loading and unloading the workpiece. Limit switch LH-4 is O
The cylinder 62 is actuated by the indexing completion confirmation signal of the table 6, and the loading/unloading table 22 moves forward together with the panties 19B. 6d confirmation signal that the general access platform 22 has advanced to the pallet exchange position (limit switch LS 2 is ON)
Accordingly, the pants) 19B are clamped to the Isoko table, and after confirming the clamping, the machine table moves a predetermined distance in the direction of removing the hook 41 of the pallet 19B from the notch 38 (perpendicular to the plane of the paper in Figure 1), and then begins the processing operation. to go into. Next, move the loading/unloading table 22 back to the backward end, replace the processed workpiece on the pant 19A indexed to the workpiece loading/unloading position with a new workpiece, and repeat the above-mentioned operation again to replace the pallet. I can do it.

Next, a second embodiment of the pallet changer of the present invention will be described with reference to FIGS. 8 to 11. The second example is
This is an example in which a gear mechanism consisting of a rack and a pinion is used as the amplification transmission means, and one loading/unloading table is installed on each of the heel loading and unloading sides.

A top lid 47 is attached to the top surface of the box-shaped base 46,
A disk-shaped table 49 (FIG. 10) having a plurality of rollers 48 that completely roll on its upper surface is placed on the top cover 47. A cylindrical portion 50 extending downward is formed on the outer periphery of the table 49, and a plurality of guide rollers 51 installed upright around the upper surface of the upper lid 47 are in contact with the outer periphery of the cylindrical portion 50 of the table 490. , table 49
Guide on 0 rotation motion. A motor 52 is attached to the lower surface of the upper M47 facing upward, and the output shaft 52 of the motor 52
The small gear 53 keyed to A is connected to the table 490.
It meshes with a large-diameter gear 54 formed on the lower outer periphery of the cylindrical portion 50 to rotate the table 49 clockwise and counterclockwise.

Two guide rails 55A and 55B each having a rectangular cross section are attached to the upper surface of the table 49, facing each other in the radial direction. A plurality of vertical guide rollers 56 and horizontal guide rollers 57 are attached to the guide rails 55A and 55B to guide the loading and unloading of pants 58A and 58B.

Two parallel guide rails 59A and 59B having a length approximately half the diameter of the table 49 are bolted to the upper surface of the top cover 47 in the diametrical direction of the table 49. The guide rails 59A, 59B have guide grooves 6O over their entire length.
A, 60B are formed in the guide grooves 6OA, 60B,
A plurality of rollers 6 are attached to both sides of the carriage 61.
2A and 62B are guided in their vertical positions, and the carriage 61
can reciprocate in the radial direction along the guide grooves 6OA and 60B. The table 49 and the upper lid 47 have a carriage 6
Relief grooves 66 and 64, which are slightly wider than the width of the carriage 61, are formed to allow full reciprocating movement of the carriage 61. Also,
Two left and right guide plates 65A and 65B (slightly shorter than the diameter of the table 49) that sandwich the upper part of the carriage 61 from both sides are bolted to the top surface of the table 49, allowing the movement of the carriage 61 to reciprocate. It is supported at the top. However, as shown in FIG. 8, when the carriage 61 is pulled in the most and is in a state of mind, the protruding portion 61A of the carriage 61 is attached to the table 4.
In order to enable the table 49 to be rotated and indexed in this state without interfering with the protrusion 61A of the carriage 61, the guide plates 65A and 65B have an arc-shaped relief 66A at the center of the table. , 66B are formed.

The guide rail 59A is provided on the lower surface of the upper lid 47.

A cylinder 67 is installed parallel to 59B, and cylinder 6
The tip of the piston rod <57A protruding from 7 is screwed to an L-shaped bracket 68. The bracket 68 is bolted to the lower surface of the carriage 61.

Therefore, when the piston rotor 7At reciprocates, the carriage 61 reciprocates along the guide rails 59A, 59B. A shaft 69 is screwed onto the upper end surface of the protrusion 61A of the reciprocating table 61, and a pinion 71 is rotatably supported on the shaft 69 via a needle pair/guar 0. The book racks mesh together at the same time.

On the upper surface of the table 49, guide rails 72A and 72B for loading and unloading tables, which are slightly shorter than the diameter of the table 49, are bolted to the inside of the two guide rails 55A and 55B that guide the loading and unloading of pallets. There is. Guide rail 7
2A, 72B are formed with guide grooves 73A, 73B in the left and right direction for loading/unloading platforms 75A, 75B (to be described later) on the top and bottom surfaces thereof, and guide grooves 74A, 74B in the vertical direction for loading/unloading tables 74A, 74B on the side surfaces. . U-shaped cross-section loading/unloading tables 75A, 75
B includes a plurality of guide rollers 76A and 76B that move within the guide grooves 73A and 73B, and guide grooves 74A and 74.
Since several guide rollers 77A and 77B that roll in B are attached, the J loading/unloading tables 75A and 75B can reciprocate in the diametrical direction of the table 49 along the guide rails 72A and 72B. be. Each loading/unloading table 75A, 75B
Racks 78A and 78E having a length corresponding to the pallet loading/unloading stroke are formed on the side surfaces of the racks 78A and 78E, and are engaged with the pinion 71 from both sides.

At one end of each loading/unloading table 75A, 75B, there is a pallet 58A.
, 58B are pivotally connected to hooks 79A, 79B that can be engaged with the hooks 80A, 80B. nail 80
A, 80B are constantly urged by springs 81A, 81B in the direction of engagement with the hooks 79A, 79B.

In addition, in the second practical example of the present invention, the structure differs from the first embodiment in which only the loading/unloading table at the loading/unloading person's position is allowed to slide and the loading/unloading tables at other positions are prevented from sliding. Different engagement means are provided. That is, near the center of the table 49, hollow guide tubes 82A and 82B are bolted directly below the loading and unloading tables 75A and 75B, and inside the guide tubes 82A and 82B, springs 83A and 83B are used to keep the cylinders in place. Locking pins 84A and 84B that are biased upward are vertically slidably inserted. Pin holes 85A and 85B are drilled in the lower surfaces of the loading and unloading tables 75A and 75B, so that when the locking bins 84A and 84B protrude upward, they enter the table 49 and the entire table 49 of the loading and unloading tables 75A and 75B is inserted. Identify against.

In addition, on one side near the center of the upper surface of the upper cover 47, there are shown in Fig.
A semi-cylindrical cam plate 86 as shown in FIG. 11 is bolted. The entire cylindrical outer circumference of the cam plate 86 has a
A downward lead from the entrances on both sides to the center and across the center? A cam e86A is formed. Furthermore, cam followers 87A and 87B that fit into the cam groove 86A are attached to the lower ends of each of the locking pins 84A and 84B. As shown in Figure 10, 1 is indexed to the carry-out person position.
@The locking pin 84A corresponding to the loading/unloading table 75A is pulled down against the spring 83A due to the interaction between the cam groove 86A and the cam follower 87A, and is pulled out from the bottle hole 85A and removed from the loading/unloading table 75A. Allows for full sliding.

The loading/unloading table 75B on the opposite side has a locking member 784B fitted into the pin hole 85B under the action of a spring 86B, completely preventing the loading/unloading table 75B from sliding.

The above-mentioned engaging means acts effectively during the rotation of the table 49 and completely prevents the loading/unloading tables 75A, 75B from flying out due to centrifugal force. That is, table 4
Even during 90 rotations, the 10,000 locking pin is always inserted into the pin hole of the loading/unloading table, so the other loading/unloading table (the side where the locking pin is removed) is inserted through the pinion 71'. The second example of the pallet changer of the present invention is constructed as described above and operates as follows. In the initial state, as shown in FIG. 8, the carriage 61 is at the backward end, the left guide rail 55A is empty, and the right guide rail 55B is loaded with a pallet 58B on which a workpiece to be used next is attached. It is placed. The hook 79B of the baren 58B is engaged with the claw 80B of the loading/unloading table 75B. When processing of the workpiece on the pallet 58A placed on the machine table is completed, the machine table moves to the pallet exchange position. When the machine table reaches the pallet exchange position, cylinder 6
7 operates to move the carriage 61 forward. In addition, the shuttle bus 6
1, before the machine table reaches the pallet exchange position,
It may be arranged so that it reaches the forward end. As mentioned above,
The loading/unloading table 75B is prevented from moving because the locking via 84B is fitted, and it is movable because the loading/unloading table 75AU locking pin 84A is pulled out. Only the entering platform 75A moves forward.

As the carriage 61 moves forward, the loading/unloading table 75Ak moves forward while rotating on the pinion 71, so that the moving distance of the loading/unloading table 75A is twice the moving distance of the carriage 61.

When the loading/unloading table 75A reaches a certain primary pallet exchange position at the forward end (indicated by the two-dot chain line in FIG. 8), the pallet 58A's 7
The locking operation between the claw 79A and the claw 80A of the loading/unloading table 75A is completed, and in response to this confirmation signal, the cylinder 67 is operated in the reverse direction, and the carriage 61 is retreated to the rear end together with the loading/unloading table 75A. Next, the motor 52 operates and the table 49?
Rotate 180 degrees counterclockwise as viewed in the plan view of FIG. 9.

Due to the rotation of the table 49, the locking pin 84AU cam groove 8
The action of the cam 7 oror 87A and the spring 83 that fully rotates within 6A
When the table 49 is gradually pulled up by the action of A and rotated approximately 45 degrees, the locking pin 84A is pulled up by the locking pin 86A.
is completely inserted into the pin hole 85A, and the locking pin /84
The cam 7 orer 87A of A separates from the cam +g 86 A. 45 before table 49 completes 180 degree rotation
The cam follower 87 of the other locking pin 84B is
B is cam groove 8<5 A VC is inserted, and IL pin 84B
starts pulling out from the pin hole 85B. table 49 is 1
80 degree rotation sound completed, pallet 58B to be used next
? When indexed to the pallet unloader position on the left side of FIG. 8, the locking bin 84B is completely pulled out from the pin hole 85B of the loading/unloading table 75B, allowing the loading/unloading table 75B to slide.

By the indexing completion confirmation signal of the table 49, the cylinder 6
7 operates again and the pallet 58B is placed on the loading/unloading table 75B'.
move forward together. In response to a confirmation signal that the loading/unloading table 75B has advanced to the pallet exchange position, the pallet 58B is clamped to the machine table, and after the clamping is confirmed, the machine table moves in a direction perpendicular to the plane of the paper in FIG.
B's fufu 9B is removed from the claw 80B of the loading/unloading table 75B, and processing operation begins. Then actuate cylinder 67 in reverse,
The loading/unloading table 75B is moved back to the fully retracted end, the processed workpiece on the pallet 58A indexed to the workpiece loading/unloading position is replaced with a new workpiece, and the above-described operations are repeated again to complete the pallet exchange.

In the above-described practical example of the present invention, the case where there are two pallets has been described, but the present invention can also be applied to a pallet changer that stores a large number of pallets.

As described above, the present invention is not limited to the configurations shown in the practical examples, and modifications are expected within the scope of the technical idea of the present invention as described in the claims.

[Brief explanation of the drawing]

Figures 1 to 7 show the first part of the pallet changer of the present invention.
A real gun example? Fig. 1 is an overall vertical sectional view, Fig. 2 is an overall plan view, Fig. 6 (A) is an enlarged sectional view taken along line AA in Fig. 1, and Fig. 3 (B) is an id Fig. 6. (B arrow view of A>,
4 is a plan view of FIG. 5, FIG. 5 is an enlarged vertical cross-sectional view of the center of the table, FIG. 6 is a plan view of FIG. 7, and FIG. 7 is a view taken along arrow C in FIG. 8 to 11 show a second embodiment of the pallet changer of the present invention, and FIG. 8 is an overall vertical sectional view;
FIG. 9 is an overall plan view, FIG. 10 is an enlarged sectional view taken along line DD in FIG. 8, and FIG. 11 is a plan view of the cam plate. In the figure, 1...Base 6...Table 22...Carry-in/out table 27--Lever 62...Cylinder 38...Notch 41...Hook 42...Circle<j43...Sho-shape Wei 46...pace 49...table 6
1... Reciprocating table 67... Cylinder 71... Binion 75A, 75B... Loading/unloading table 78A, 78B
...Rack 79A, 79B...Hook 80A,
80B...claw 84A, 84B...locking bit/86
...Cam Itade 1 person Hitachi so-called machine type company Figure 6 Figure 7

Claims (1)

[Claims] a base; a table provided on a loop-shaped guide on the base so as to be rotatable and indexable in a horizontal plane; a drive source for rotatably indexing the table; and a table located between the upper surface of the base and the table and rotatable in the radial direction. A first guide rail extending from the center and provided on the base, and a gear provided on the first guide rail so as to be freely forward and backward and rotatable about an axis parallel to the table rotation center. a reciprocating carriage having a drive source provided on the base for reciprocating the reciprocating carriage along a first guide rail, and a drive source provided on the table parallel to the guide body and corresponding to two pallets, respectively. a second guide rail that guides a pair of pallets; a pair of third guide rails that are provided on the table inside and parallel to the second guide rail and opposite to the table center line; Each of the third guide rails is slidably provided with a rack that engages with the gear of the carriage from both sides, and has an engaging portion at its tip that can be detachably engaged with an engaging piece of the pallet. and a holding means provided on the table for positioning the loading/unloading platform holding the other pallet when one pallet is unloaded by the advancement of the carriage. .