Pallet changer for machining center

A pallet changer device is associated with a milling or machining device and has a table that indexes 180.degree.. A pallet is held in an upright position for loading of fresh workpieces, while machining is carried out automatically on workpieces on a similar pallet. When the machining is complete, the table indexes 180.degree. exposing an available station, and an arm retrieves the pallet of machined parts and moves it onto the table. Then the table is indexed again, and the pallet of fresh workpieces is moved to a work station at the machining device. A wash cycle is carried out on the pallet of workpieces, now suspended beneath the inverted table. After the cycle, the table is inverted placing the cleaned finished workpieces upright. These are removed from the pallet and replaced with fresh workpieces.

BACKGROUND OF THE INVENTION 
This invention relates to milling or machining apparatus, and auxiliary 
equipment therefor, and is more specifically directed to a device that 
handles pallets on which are mounted workpieces that are to be positioned 
at a work station adjacent the milling or machining apparatus. 
The invention is more particularly concerned with a device in which raw 
workpieces can be mounted on an upper surface of a pallet on the device, 
after which the device automatically positions the pallet and its 
workpiece or workpieces at the milling or machining work station, and 
brings out from the work station a similar pallet containing parts which 
have been suitably machined by an earlier operation. The latter pallet is 
brought to a cleaning or working station within the device where metal 
chips and other milling debris are washed and/or blown from the finished 
parts and from the pallet, after which the pallet is positioned so that an 
operator can remove the finished parts and replace them with fresh, 
unmachined workpieces. 
It is the current practice for an operator to position workpieces by hand 
at a milling machine, or if a pallet is employed for carrying the 
workpieces, to position the pallet by hand at a work station beneath the 
head of the milling machine tool. 
An automatic set-up system for providing palletized work to be machined by 
an automatic machine tool has been proposed in U.S. Pat. No. 4,543,970. In 
that system the pallet is conveyed to the machining device, and the pallet 
and work that is clamped to it are fed into a cleaner where debris and 
chips are washed from the pallet and the machined parts. This system is 
rather complex and elaborate and is not readily field installable or 
retrofittable onto existing machining equipment. The system cannot be made 
compactly enough to be positioned alongside a milling center or the like. 
Also, the setting table and cleaner are in separate units, and an 
elaborate conveyer system is required to carry the pallets among its 
various stations. In addition, no effort has been made to address the 
problem of misalignment which can occur if metal chips or debris work 
themselves between a pallet and the bed of the milling machine on which 
the pallet sits. This is a significant problem, as an error of less than 
one mil can be sufficient to require scrapping of an entire batch of 
machined parts. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide a pallet changer device to be 
used in conjunction with a milling machine or other metal working machine, 
which removes, without an attending operator, pallets of finished 
workpieces from the machine and replaces them with pallets of fresh 
workpieces or workpieces still to be machined by the same process. 
It is another object of the invention to provide the device with a 
programmable controller which automatically orchestrates the pallet 
changing and machining operation, and which can be signalled from a 
control panel to initiate the operation. 
It is yet another object of this invention to provide the pallet changer as 
a compact, field-installable device which is universal, i.e., can be used 
with almost all milling machines or machining centers and can be installed 
so as to load pallets from the side of the milling machine or machining 
center. 
It is a still further object of this invention to provide the pallet 
changer with an upwards biasing cam locking system which holds the pallets 
in place in such a way that machining debris and metal chips will not 
interfere with the accurate registration of the pallet and workpieces. 
It is yet a further object of this invention to provide a pallet changer in 
which a wash cycle is automatically carried out and in which the pallet 
with the washed, machined parts is returned to a position where an 
operator can remove the machined parts from the pallet and replace them 
with fresh workpieces and after which he or she can initiate the cycle 
anew. 
It is another object of this invention to increase machine tool utilization 
time by reducing the machine down time for loading, keeping the down time 
limited only to the small amount of time required for the pallet changing 
device to exchange a pallet of machined workpieces with a pallet of fresh, 
unmachined workpieces. 
It is still another object of this invention to maximize the operator 
safety factor by permitting completely unattended operation of the 
machining center or milling machine, and eliminating any need for an 
operator at the spindle area of the machining center or milling machine 
during a machining operation. 
A still further object of this invention is to provide a pallet changer 
device that will accommodate pallets of various configurations and sizes, 
so as to fit the user's needs, which accommodates either manual or 
automatic pallet loading, which integrates easily into a pallet pool line, 
and which reduces workpiece changeover time to a bare minimum. 
In accordance with an aspect of this invention a universal 
field-installable pallet changing, loading, and cleaning apparatus 
automatically brings a pallet containing at least one workpiece to a work 
station, and precisely locates that workpiece in position for machining at 
an automatic machining device, and thereafter retrieves the machined 
workpiece and pallet, cleans it, and exchanges it with another. The pallet 
has an upper side that includes means for clamping or otherwise holding at 
least one workpiece to be machined. Its underside is provided with flanged 
rails that extend in a longitudinal direction. An indexing work station is 
disposed adjacent the machining device. This work station has rails which 
slidably receive the pallet rails, and stop means for locating the pallet 
accurately at a predetermined position with respect to the spindle or 
similar machining means of the machining device. At the work station, a 
cam biases the pallet upwards when the pallet is at the predetermined 
position. This locks the flanges of the pallet rails against flanges of 
the station rails. A loading and cleaning station has a housing in which 
there is mounted an invertable table that is journalled along its 
horizontal axis, and has a pair of opposed base plates on opposite sides 
of the axis. There are flanged longitudinal rails on each table base plate 
for slidably engaging the pallet rails and for permitting transfer to and 
from the work station. Cams are also provided on these table plates for 
biasing the pallets away from the plates so as to engage the flanges of 
the pallet rails with the rail flanges of the invertable table. A 
displacement arm engages a projection on the pallet and moves the same 
between the invertable table and the work station. This positions the 
pallet containing fresh workpieces under the machining device, and then 
when the machining operation is complete, removes the pallet containing 
finished workpieces back to the invertable table of the loading and 
cleaning station. A drive mechanism rotates the table at the appropriate 
times, indexing it 180.degree., to invert the same when the pallet 
containing the workpieces is in place on it. A washing or cleaning device, 
e.g. a sprayer, within the housing washes debris from the inverted pallet 
and from any workpieces mounted on it. 
Control means coordinate the operation of various parts of the system and 
actuate the work station and the loading and cleaning station so that the 
system operates generally in the following fashion. While the machining 
device is automatically machining workpieces on one pallet at the work 
station, an operator can be reloading another pallet which is available at 
the loading and cleaning station. The operator loads the workpieces onto 
preset fixtures, i.e. vises, clamps, etc., at Positions appropriate for 
the particular machining process involved. After this pallet has been 
loaded, the operator presses a button on a control panel of the control 
means. This causes the pallet of unmachined parts and the invertable table 
that holds the pallet, to index 180.degree., and to hang "upside down" in 
the loading and cleaning station. This indexing operation causes a vacant 
station, i.e. on the opposite plate of the invertable table, to be 
positioned on top, awaiting the completion of the machining of workpieces 
on the pallet which is then at the work station, under the machining or 
milling center. 
When the machining of parts is completed, the control means automatically 
condition the work station mechanism for removal of the pallet. The 
displacement arm, which can be a gear driven arm as in the preferred 
embodiment, moves forward from the pallet loading and cleaning station and 
grasps the pallet of finished machined workpieces. This arm then pulls the 
pallet back from the machining device work station and slides the same in 
place on the available side of the invertable table. The camming devices 
are actuated to lock the pallet in place. Then the invertable table is 
indexed 180.degree.. This presents a pallet that is loaded with fresh, 
unmachined workpieces in an upward position. The gear driven arm, or other 
displacement mechanism, is then automatically actuated to shuttle the 
pallet of fresh workpieces onto the work station of the machining device 
table. 
At the same time, as soon as the invertable table has been indexed, a wash 
cycle is commenced to remove metal chips or other machine debris from the 
inverted pallet and the finished parts that are carried on it. This wash 
cycle can be carried out by means of several spray arms that are carried 
on a trolley. The trolley with spray arms traverses beneath the suspended 
pallet inside the housing of the loading and cleaning station. After a 
number of wash cycles, a valve is appropriately actuated to apply 
compressed air to the spray arms so as to blow dry the pallet and parts. 
The number of wash cycles and blow dry cycles can be programmed to clean 
the parts within a reasonable cycle time. 
At the completion of the washing and drying operation, the table is once 
again indexed 180.degree. to bring the pallet and the cleaned, finished 
parts to an upward position. At this time, the operator can remove the 
machined articles and replace them with fresh unmachined workpieces, at 
which time the cycle is again initiated. 
The camming mechanism wedges the pallets upwards so that horizontal flanges 
of the rails inter-engage with each other. Thus, any machining debris is 
kept away from the mating surfaces of the rail flanges. This eliminates a 
major cause of machining error, and automatic placement of the pallets and 
their workpieces can be accurately and repeatedly carried out. This 
eliminates a major reason for out-of-tolerance machining. On the top of 
the loading and cleaning station, there are a pair of hinged cover flaps 
that extend from the sides of the housing to the edges of the pallet 
carried on the invertable table. These can be elevated open to provide 
clearance when a table indexing operation is to take place, but lowered to 
close at other times. These cover flaps prevent an operator from placing 
his or her hand into the machine during a cycle, and also prevent operator 
tools, such as screwdrivers, allen wrenches, or the like, from falling 
from the pallet or table into the machine. The covers also serve to keep 
the sprayed cleaning fluid from escaping out from the top of the loading 
and cleaning station. 
The above and many other objects, features, and advantages of this 
invention will be more fully understood from the ensuing detailed 
description of a preferred embodiment, which is to be considered in 
connection with the accompanying drawing.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
With reference to the drawing, FIG. 1 shows the general layout of a 
universal, field installable pallet changing system 10. Generally, the 
system comprises a floor-mounted pallet changing, loading and cleaning 
station 11 which automatically feeds and receives pallets 12 on which 
workpieces 13 are secured by hold down clamps or vises 14. The pallet is 
automatically transferred between the pallet changing station 11 and the 
bed or table 15 of a machine tooling device 16, here a vertical milling 
center. As further explained with reference to FIGS. 2 and 3, the pallet 
changing station 11 has a housing 17 and a table 18 (FIGS. 6 and 7) which 
is journalled for 180.degree. rotation along a longitudinal axis 19 
thereof. To this end, a drive sprocket 20 is affixed on the axis 19 at the 
side away from the milling center 16. Cover flaps 21 are hinged to side 
edges of the housing 17 and extend inwards, at least to the location of 
edges of the pallet 12. These are lifted for clearance to permit 
180.degree. indexing of the table 18. A washer mechanism 22 is disposed 
within the housing 17 and beneath the table 18. This mechanism 22 includes 
a trolley 23 that has a number of spray arms 24 mounted on it, and a 
hydraulic motor 25 which moves the trolley 23 longitudinally back and 
forth along rods 26 within the housing 17. A motor 27 and transmission 28 
apply drive forces to a drive chain 29 to rotate the sprocket 20, and with 
it the table 18. 
A debris collection drawer 30 slides in and out of the housing 17 beneath 
the washing mechanism 22. This contains a screen to remove machining 
debris and chips of metal from the oil or cleaning fluid that is sprayed 
by the arms 24. 
The pallet 12, as shown in cross section in FIG. 2, on its lower side 31 
has a pair of L-shaped flange rails 32, while the table 18 has on an upper 
plate 18a thereof, a set of mating L-shaped flange rails 33. The table 
also comprises a sufficient number of longitudinal guide assemblies 34, 
with both vertical and horizontal rollers, to guide the pallet 12 into 
position on the table 18. 
An indexing device, as shown in FIG. 2, comprises a cam wheel 35 mounted on 
the table axis 19 at the distal end of the table 18, that is, that the end 
facing the milling center 16. This cam wheel 35 has cams 36 disposed at 
180.degree. spacing, which actuates a cam follower micro switch 37. The 
cam wheel 35 also carries a pair or radially extending lugs 38. A ram 
actuator 39 moves a key member 40 laterally to lock onto an associated one 
of the lugs 38 to hold the table 18 against rotation when not desired. 
Also shown in FIG. 2 is a motor 41 for powering an express arm 42 which is 
slidably mounted alongside the housing 17 of the pallet changing and 
cleaning station 11. This arm 42 is comprised of inner and outer sleeves 
42a, 42b, which carry a toothed rack 43 driven by a pinion gear 44 (See 
FIG. 4) that is driven by the motor 41. A microswitch 45 senses the 
presence of the end of the rack 43. 
A finger mechanism 46 is disposed at the distal end of the express arm 42 
(as shown in FIGS. 5, 13, and 14). The finger mechanism couples with a 
pallet arm 47 that is affixed onto the pallet 12, and protrudes laterally 
a sufficient distance to contact the finger mechanism 46. The latter 
comprises a fixed finger 48 which carries a rubber bumper 49 that pushes 
against the pallet arm 47, and a movable finger 50, which can be 
selectively moved for pulling against the front or distal side of the 
pallet arm 47 to remove the pallet back onto the table 18 of the station 
11. The above members are mounted in a frame 52 for the finger mechanism 
46. 
As shown more specifically in FIGS. 6 and 7, the table 18 is formed of an 
upper plate 18a and lower plate 18b, which are substantially identical. 
The plates 18a and 18b carry the L-shaped rails 33 as illustrated, with a 
horizontal flange 53 disposed away from the surface of the plate 18a, 18b, 
and a vertical web 54 joining the flange 53 to the plate 18a, 18b. 
Also shown in FIGS. 6 and 7, each table plate 18a, 18b has several camming 
lock devices 55 which are hydraulically actuated and are connected by 
hydraulic lines or conduits 56 to a union connector 57. As shown in FIGS. 
8-10, each camming device 58 is formed of a shoe or block 58 affixed onto 
the surface 18a, 18b, with a T-shaped camming member 59 contained therein. 
A hydraulic ram 60 is mounted in one end of the shoe 58, with the T-shaped 
camming member being mounted opposite it. Alternatively, the ram 55 could 
be a pneumatic cylinder or a solenoid. A return compression spring 61 is 
mounted in an end wall of the shoe 58 for urging the camming member 59 
towards the ram 60. 
Cross bars of the T-shaped camming member 59 ride in vertical slots 62 of 
the shoe 58, while a tongue 63 of the camming member rides along the 
surface of the associated plate 18a, 18b. When the hydraulic pressure is 
relieved from the lines 56, the ram 36 is relaxed and the spring 61 urges 
the member 59 into its recumbent position as shown in FIG. 9. In this 
condition, the pallet 12 can be slid onto the rails 33 with clearance 
between the flanges of the rails 32 and 33, as shown in FIG. 11. 
Thereafter, hydraulic pressure in the lines 56 causes the rams 60 to urge 
the members 59 to an erect position, as shown in FIG. 10. This raises the 
pallet 12 away from the table plate 18, and brings the flanges of the 
respective rails 32 and 33 into contact. Because of the upward locking 
condition, debris or machining chips are highly unlikely to fall onto the 
mating surfaces of these flanges, so that it is extremely unlikely that 
any machining debris would cause errors in alignment of the pallet and the 
associated workpieces 13. FIGS. 15 and 16 illustrate the arrangement of a 
so-called indexing unit 65 which is disposed on the table or bed 15 of the 
milling center 16. The arrangement of this indexing unit 65 is quite 
similar to that of the table plates 18a, 18b, and comprises 
L-cross-section rails 66 as well as guide rail and wheel assemblies 67. A 
locator post 68 is situated on the indexing unit 65 for accurately 
positioning the pallet 12 at the work station. A plurality of hydraulic 
lines 69 are each associated with camming devices 55. These devices 55 are 
identical with those discussed with reference to FIGS. 8-12, and serve the 
same purpose, namely urging the pallet upwards for accurately positioning 
the pallet 12 and workpieces 33, and locking the flanges of the pallet 
rails 32 against flanges of the indexing unit rails 66. 
With reference to FIG. 17, and also to FIG. 1 and FIG. 2, the housing 17 
for the pallet changing, loading and cleaning station 11 has the covers 21 
hingedly mounted at the top of side walls 70, and diagonal walls 71 
beneath the washer mechanism 22 extend to a cleaning solvent or fluid well 
72 at the bottom of the station 11. Leveling screws 73 are disposed at 
each corner of the base of the station 11 for leveling the same and 
placing the table 18 at the appropriate height with respect to the 
indexing unit 65 at the work station 15. 
As shown in FIG. 17, a pair of hydraulic pistons 74 and associated linkages 
serve to lift the cover flaps 21 at the appropriate times for rotating the 
table 18, and a pair of hydraulic pistons 75 serve to lift a frame 76 on 
which the wash mechanism 22 is suspended. This brings the spray arms 24 
upwards during a wash and blow dry cycle. Hydraulic connectors 77 feed 
hydraulic fluid through the sprocket 20 to each of the unions 57 so that 
the appropriate group of the cam devices 55 can be actuated or relaxed as 
appropriate. Also, as shown in FIG. 1, a controller 78 includes an 
operating console 79. This controller 78 is programmable to adjust the 
wash and blow dry cycles to allow the washing to occupy the maximum amount 
of time available, taking into consideration the amount of time required 
for a machining cycle on the machine center 16, and the amount of operator 
time required for removing the finished workpieces 13 from the pallet 12 
and installing new workpieces thereon. 
The station 11 can be positioned between machine centers 16 on a pallet 
line for washing and holding the pallets and parts between successive 
machine steps. Also, the station 11 can be used in connection with a 
pallet distribution and storage station, which stores a large number of 
preloaded pallets and then supplies them one at a time, to the pallet 
changing and cleaning station 11. The latter automatically feeds the 
pallets that carry unfinished workpieces 13 to the milling center 16. The 
pallet 12 carrying finished machined parts 13 is then returned to the 
pallet changing and cleaning station 11, and the finished parts are 
cleaned therein. Then the pallet with the clean, finished parts can be 
returned to an appropriate location in the automatic distribution and 
storage station. 
It should be emphasized that the system of this invention reduces workpiece 
change-over time to an absolute minimum, and permits loading and unloading 
of workpieces simultaneously with the ongoing machine cycle. Pallet line 
integration is facilitated because of the location of the pallet changing 
and cleaning station at the side, rather than in front, of the milling 
center or other machining mechanisms 16. This system can be readily field 
retrofitted onto virtually any existing milling or machining center, and 
can be integrated easily into a pallet pool line or into a flexible 
machining system. Because of the upward camming movement of the camming 
devices 55, metal flakes, chips, and grindings do not present any problem 
for the accurate and repeatable positioning of pallets at the work 
station. With this system operator intervention is kept to a minimum, and 
completely unattended operation is possible. Pallets 12 of various 
dimensions, as appropriate to the machining operation or operations to be 
performed. The pallets 12 need not be strictly flat pallets, but T-slotted 
pallets, sub-plate type pallets, and other pallets, as required for the 
machining of particular parts, can readily be employed. 
The automated feed cycle for the system 10 is generally as follows. In 
operation, there is a pallet 12 with workpieces 13 mounted on it at the 
work indexing unit 65 at the machining work station. When the machining 
work is finished, this pallet 12 is returned by the displacement arm 42 to 
the invertable table 18. To accommodate this, the covers 21 are first 
lifted. The cam mechanisms 55 are actuated to hold the pallet 12 in place 
on the table 18, and then the table 18 is inverted 180.degree. so that the 
pallet and the machined workpieces 13 thereon face the washer mechanism 
22. At that time another pallet 12 containing fresh workpieces 13 is moved 
from the other side of the table 18, which is now disposed upwards to the 
indexing mechanism 65. Then the express arm releases itself from the 
second pallet 12 and returns to a standby position. The cover flaps 21 are 
lowered, and the washer mechanism 22 begins its spray washing of the 
inverted pallet 12 and the finished workpieces 13. After a sufficient 
number of cycles of washing and blow drying, the cover flaps 21 are raised 
and the table 18 is then inverted, bringing the pallet 12 with the 
finished workpieces 13 back to the top. At this time, the covers are 
dropped back to the closed position, and an operator can simply remove the 
finished parts from the pallet by releasing the vises 14, and can install 
fresh workpieces to be machined back onto the top of the pallet 12. When 
the machining cycle is finished, this newly ready pallet of workpieces is 
inverted on the table 18, and the pallet changing and cleaning station is 
ready to receive the finished parts and exchange them with other 
unfinished workpieces. Because all of this takes place in only a few 
seconds, the machining or milling center can be utilized on a work cycle 
that is close to 100%, which is substantially double the effective work 
cycle using a manual loading system. 
While the invention has been described in detail with respect to a 
preferred embodiment, it should be understood that the invention in not 
limited to that embodiment, and that many modifications and variations 
could be effected without departing from the scope and spirit of this 
invention, as defined in the appended claims.