Industrial robot

An industrial robot, having a manipulative robot hand for mounted on a vertically movable portion thereof moved by a vertical drive, provided with a load reducing pneumatic cylinder for applying a constant upward force to the vertically movable portion during the vertical movement of the portion and an air storage tank or tanks directly connected to the pneumatic cylinder for continuously supplying air under a desired fixed pressure. The upward force contributes to reducing a load applied to the vertical drive. The air storage tank or tanks contributes to ensuring mechanical rigidity of the industrial robot.

DESCRIPTION OF THE INVENTION 
The present invention relates to an industrial robot operating as an 
industrial manipulating device, more particularly to an industrial robot 
with an improved load reducing means capable of reducing the load applied 
to an actuator, for example, a feed motor, for driving the vertically 
movable portion of the robot. 
Industrial robots are conventionally employed for, for example, numerically 
controlled machine tools, as industrial manipulating devices transferring 
workpieces to and from the machine tools or loading and unloading 
workpieces to and from the machine tools. 
Industrial robots are equipped with manipulator robot hands capable of 
transverse expansion or contraction. The robots are also equipped with 
means for moving the robot hand vertically and means for rotating the 
robot hand in a horizontal plane, thereby enabling the robot hand to be 
brought to the desired position. For the purpose of vertical movement of 
the robot hand, the robots are structured with one or more guide pillars 
along which a portion of the body can be vertically moved by means of an 
actuator, for example, a feed motor. The above-mentioned robot hand is 
mounted on this vertically movable portion so as to be transversely 
expandable and contractable. Accordingly, it is necessary that the 
actuator have a considerably large drive power, enough for driving the 
vertical movement of that portion of the body while supporting the load of 
the workpiece gripped by the robot hand, the weight of the vertically 
movable portion and the robot hand, and the mechanical moment acting on 
the vertically movable portion. 
It has already been proposed to provide industrial robots equipped with 
load reducing means to reduce the load applied to the actuator. One 
example of an industrial robot equipped with a load reducing means is 
disclosed in U.S. Pat. No. 4,289,441, granted on Sept. 15, 1981. The load 
reducing means comprises a cylinder means capable of applying, to the 
vertically movable portion, an upward force corresponding to the downward 
load acting on the actuator, thereby reducing the load applied to the 
actuator. This conventional load reducing means, however, is arranged to 
maintain the upward force given to the vertically movable portion at a 
continuously constant level by discharging the air, which had been 
compressed to a high pressure within the cylinder means during the 
downward movement of the vertically movable portion, out to the atmosphere 
by way of a relief valve. 
Consequently, the energy used for operating the pressurized air source had 
been wasted by the discharge of pressurized air to the atmosphere. The 
discharge of pressurized air once used for the cylinder means into the 
atmosphere also often became a cause of environmental pollution due to its 
oil component as the air supplied to the cylinder means is usually mixed 
with a mineral oil. 
Accordingly, demands have arisen for the above-mentioned disadvantages to 
be eliminated, i.e., for improvements to be made for greater energy 
savings and for prevention of environmental pollution. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an industrial robot 
equipped with a load reducing means which meets the above-mentioned 
demands. 
In accordance with the present invention, the industrial robot comprises a 
manipulative robot hand, a vertically movable portion supporting the robot 
hand thereon, a vertical drive means for effecting vertical movement of 
the vertically movable portion guided by a vertical guide pillar or 
pillars, the vertical drive means including a vertical feed motor, a 
pneumatic cylinder means for applying an upward force to the vertically 
movable portion, air storage means arranged between a pressurized air 
source and the pneumatic cylinder means for storing air under pressure 
therein, and air conduit means for providing a direct connection between 
the air storage means and the pneumatic cylinder means. 
The arrangement wherein the pneumatic cylinder means and the air storage 
means are directly connected to effect continuous supply of pressurized 
air from the air storage means to the pneumatic cylinder means enables the 
use of a pressurized air source, i.e., an air compressor, with a supply 
capacity only large enough to replenish the air storage means at a supply 
rate corresponding to the leakage of air from the air storage means. 
At this stage, it should be understood that in the conventional load 
reducing means of an industrial robot, pressurized air is supplied 
directly from an air source to a cylinder means for applying upward force 
to the vertically movable portion of the robot. After the pressurized air 
is discharged from the cylinder means to the atmosphere, the air source 
has to resupply pressurized air to the cylinder means. Accordingly, the 
successive operation of a large-capacity air source, such as an air 
compressor, is inevitable. 
The present invention represents a considerable improvement in respect to 
energy savings.

Referring to FIG. 1, an industrial robot has the load reducing means 
described below. A base structure is designated by reference numeral 10. A 
vertical drive means including a vertical feed motor and a pneumatic 
cylinder are both built in the base structure 10. A vertical guide pillar 
12 and a piston rod 14 of the pneumatic cylinder extend upright above the 
base structure 10. A vertically movable portion including a robot rotation 
means 16, a bearing box 18, a robot arm drive motor 20, a robot housing 
22, a robot arm 24, a robot wrist 26, and a robot hand 28 is adapted to 
move up and down along the vertical guide pillar 12. The pneumatic 
cylinder of the above-mentioned load reducing means applies an upward 
force to the vertically movable portion by means of the piston rod 14. 
Referring to FIG. 2, illustrating the pneumatic circuit arrangement of the 
conventional load reducing means of FIG. 1, the hatched circle referenced 
by number 30 represents the vertically movable portion of the robot 
illustrated in FIG. 1. The portion 30 is continuously subjected to an 
upward force by a pneumatic cylinder 32. The pneumatic cylinder 32 is 
supplied with air under pressure from a pressurized air source 34, such as 
an air compressor, by way of a pressure regulator 36 for regulating the 
air to a desired fixed pressure level. Therefore, the portion 30 is 
continuously subjected to a force equivalent to the product of the 
pressure set by the pressure regulator 36 and the effective area of the 
pneumatic cylinder 32. A relief valve 38 is provided for preventing an 
excessive rise in the pressure of the air resulting from the compression 
of the air within the pneumatic cylinder 32 while the portion 30 is moved 
down by a vertical drive means. That is, the relief valve 38 contributes 
to maintaining the fixed desired pressure level of the air by discharging 
the excessively compressed air therefrom into the atmosphere during the 
downward movement of the portion 30. However, the pressurized air source 
34 must resupply pressurized air to compensate for the discharged air 
after the discharge operation of the relief valve 38. Thus, the 
pressurized air source 34 must be of a large capacity and must frequently 
be operated. 
The present invention is able to provide a load reducing means which 
eliminates the disadvantages of the conventional means. 
Referring now to FIG. 3, illustrating the pneumatic circuit arrangement of 
an industrial-robot load reducing means embodying the present invention, 
the hatched circle referenced by number 130 illustrates the vertically 
movable portion of the robot. A feed motor 42, a belt-and-pulley mechanism 
44, and a feed screw mechanism 46, which are constituent elements of a 
vertical drive means for the portion 130, are also schematically 
illustrated in FIG. 3. 
In the present invention, pressurized air produced by the pressurized air 
source 134 is sent into an air storage tank 50 by way of a pressure 
regulator 136 and a check valve 48. The air storage tank 50 stores air 
under a desired fixed pressure. The air under the desired fixed pressure 
of the air storage tank 50 is supplied to the pneumatic cylinder 132 by 
way a conduit 49, so that an upward force corresponding to the product of 
the pressure of the air and the effective area of the pneumatic cylinder 
132 is applied by the piston rod 114 of the cylinder 13 to the portion 
130. The air storage tank 50 has a sufficient storage capacity. With the 
pneumatic circuit arrangement of FIG. 3, pressurized air can always be 
supplied from the air storage tank 50 to the pneumatic cylinder 132 once 
the air storage tank 50 is filled. Therefore, a conventional air 
compressor of a rather small capacity can be used as the pressurized air 
source 134. That is, the air compressor only has to be of a capacity 
sufficient to supply air under pressure to the air storage tank when the 
pressure within the air storage tank 50 drops below the desired fixed 
level set by the pressure regulator 136 due to leakage of air from the air 
storage tank 50, the pneumatic cylinder 132, or the air passage between 
the source 134 and the pneumatic cylinder 132. The upward force exerted by 
the pneumatic cylinder 132 and applied to the portion 130 is produced by 
the pressure of the air within the air storage tank 50 as well as the 
pneumatic cylinder 132. Further, the pressure within the air storage tank 
50 is constantly maintained at a desired fixed level for an extended 
period of time after the air storage tank 50 has once been filled. These 
facts also enable the use of a rather small compressor which needs less 
energy for operation. 
It should further be understood that according to the pneumatic circuit 
arrangement of FIG. 3, the upward force applied to the body 130 can be 
maintained at a fixed value. The reason will be described hereinbelow. In 
accordance with the law of a absolute pressure systems, the following 
relationship given by equation (1) is established: 
EQU V.sub.1 (P+1.03)=(V.sub.1 +V.sub.2)(P+1.03+.DELTA.P) (1) 
wherein V.sub.1 (l) is the volume of the air storage tank 50 and the 
conduit 49 connecting the air storage tank 50 and the pneumatic cylinder 
132, V.sub.2 (l) is the increase in the volume of the pneumatic cylinder 
132 due to the rise of the portion 130, P(kg/cm.sup.2 .multidot.G) is the 
desired fixed pressure, set by the pressure regulator 136, of the 
pressurized air within the air storage tank 50, and .DELTA.P(kg/cm.sup.2 
.multidot.G) is the pressure increase of the pneumatic cylinder due to an 
increase in the volume of the pneumatic cylinder 132. From equation (1), 
the following equation (2) is established: 
EQU .DELTA.P=-V.sub.2 /V.sub.1 +V.sub.2 .multidot.(P+1.03) (2) 
It should be noted from equation (2), above, that the pressure increase 
.DELTA.P becomes extremely small when V.sub.1 is sufficiently greater than 
V.sub.2. Therefore, the pressure within the pneumatic cylinder 132 is 
maintained at a substantially fixed level regardless of the increase in 
the volume of the pneumatic cylinder 132. When the volume of the chamber 
of the pneumatic cylinder 132 is reduced due to the downward movement of 
the portion 130, the increase in the pressure within the chamber remains 
very small, according to the principle explained above, since the chamber 
of the pneumatic cylinder 132 and the air storage tank 50 are directly 
connected by the conduit 49. As a result, the pressure of the air working 
within the pneumatic cylinder 132 is always maintained at a substantially 
fixed level. 
Referring to FIG. 4, the vertically movable portion of the industrial robot 
comprises a robot rotation drive means 116, a bearing box 118, a robot 
housing 122, a robot arm 124, a robot wrist 126, and a robot hand 128. 
That is, as described later, the vertically movable portion is arranged to 
be vertically movable along a vertical guide pillar 112. It should be 
noted that the robot housing 122, is rotatable about a vertical axis by 
the operation of the drive means 116. A pneumatic cylinder 132 for 
applying an upward force to the vertically movable portion is fixedly 
mounted on a robot base 52, which is the lowermost element of the robot. 
The pneumatic cylinder 132 has the piston rod 114, of which the outermost 
end is connected to a part of the vertically movable portion. If required, 
it is possible to adopt an arrangement such that the outermost end of the 
piston rod 114 is fixed to the robot base 52 and the end of the pneumatic 
cylinder 132 is connected to the vertically movable portion. A vertical 
feed motor 42, a belt-and-pulley mechanism 44, and a feed screw 46 are 
also mounted on the robot base 52. That is, the feed screw 46 is rotated 
by the feed motor 42 by means of the belt-and-pulley mechanism 44. Since 
the feed screw 46 is threadedly engaged with a female screw element 56 
provided at the vertically movable portion, the rotation of the feed screw 
46 causes vertical movement of the vertically movable portion along the 
vertical guide pillar 112. Reference numeral 58 designates a slide 
provided for the vertically movable portion and slidably engaged with the 
vertical guide pillar 112. At this stage, a pair of vertical guide pillars 
may be substituted for the single pillar 112. In the embodiment of FIG. 4, 
a pair of air storage tanks 50a and 50b are disposed, which correspond to 
the air storage tank 50 of FIG. 3. These air storage tanks 50a and 50b are 
fixedly mounted on the robot base 52, and they are incorporated in the 
robot as a rigid structure to furnish the robot with mechanical rigidity 
and stability. Reference numeral 54 designates an air conduit means 
interconnecting both air storage tanks 50a and 50b and the pneumatic 
cylinder 132. 
The use of the pair of air storage tanks 50a and 50b both for the air 
storage means and for the rigid structural means of the robot keeps to a 
minimum the increase in industrial robot dimensions as compared with 
conventional industrial robots, due to the additional air storage means 
and, conversely, ensures the rigidity of the industrial robot.