Playback system grinding robot

A playback system grinding robot is disclosed which includes a No. 2 arm attached for ocillation to the head of a No. 1 arm turning around a main axis, a drive arm arranged adjacent to the No. 1 arm so as to drive the No. 2 arm, and abrasive tool attached to the No. 2 arm head axis and pressed perpendicularly downward by a fluid cylinder to be freely turnable in different directions, and possessed of a dual degree-of-freedom of control in the polar coordinate system. A positional data generator for indicating a horizontal movement position of the abrasive tool is also provided as is a memory to store directional data together with positional data in the memory at the time of "teaching", especially to input turnback point data on the tool traveling locus exactly into the memory in accordance with a change of the directional data. A control device is included for decelerating the tool motion when the directional data are changed at the time of "playback work" and determines proper speed of the abrasive tool by using the directional data jointly with a variation in volume of the positional data. The control device also causes the abrasive tool to move in a zigzag manner, as well as a random manner on its route, thereby ensuring a manufacture of the polished products free from sharp differences in apparent surface finish between work areas and other areas.

FIELD OF THE INVENTION 
The present invention relates to a playback system die grinding robot with 
a dual degree-of-freedom of polar coordinates, and more particularly, to 
the playback system grinding robot which is so contrived that No.2 arm is 
pivoted on a head of a freely turnable No.1 arm and an abrasive tool is 
fitted to a head of said horizontally moving No. 2 arm. The die is pressed 
perpendicularly downward to be in close contact with the curved surfaces 
of the die. 
Further, the present invention relates to an entirely new and unique 
grinding robot designed to conduct an appropriate playback work in 
accordance with a the processing accuracy demanded and also does not 
create any detachable process difference on the workpiece surface to be 
ground. 
Conventionally, a three dimensional control playback system robot has been 
employed in the field of welding work, etc., however, it has been required 
to incorporate a large scale memory device and input program in its 
mechanism. And, there have been numerous cases where an abrasive tool is 
fitted to this type of grinding robot and is directly put in practical 
use, especially in grinding work of a free curved-surface. But, in such 
manufacturing industries, the problems of a large scale 3-dimensional 
memory device and input program still remain unsolved. 
However, making an analysis of the grinding work carried out by manual 
labor from the viewpoint of its operation, it may be understood that the 
work is of a simple pattern to repeat linear movements along the profile 
of a free curved-surface while pressing down the grindstone on the 
workpiece surface, and the work itself is relatively of an uncomplicated 
movement. 
From a result of such analysis, the grinding robot according to the present 
invention is so designed that the abrasive tool attached to the arm head 
is pressed perpendicularly downward by the force of an air cylinder in a 
direction of a Z-axis on the coordinate system while moving it always 
along a profile of the workpiece surface and at the same time the arm is 
capable of performing a plane movement to the directions of an X-axis as a 
well as Y-axis. Namely, the present invention aims to provide such a 
grinding robot wherein is possible to exactly control the abrasive tool 
motion merely with the positional data of X- and Y-axes of the coordinate 
system and to minimize the memory device, and to stabilize the playback 
action without using any input program. 
In the grinding work of this type grinding robot, as the points on the 
locus that the abrasive tool has to travel exist innumerably, it is 
practically impossible to fully memorize these points one by one at the 
time of the "teaching" operation. Therefore, in the prior art, the 
operator has hitherto given a memory instruction of the travel point in an 
optional position on the locus to the robot at the time of "teaching" and 
the robot has stored the positional data pertaining to the said travel 
point it has been instructed to memorize. 
By the way, the grinding work is not always demanded to have a uniform 
process accuracy all over the workpiece surfaces. Generally, in 
complicated shape portions, it is required to process to a highly precise 
condition, and in uncomplicated plane portions, it is not necessary to the 
peice so accurately. Therefore, in some of the conventional robots, the 
operator has given a memory instruction cautiously to the robot whenever 
he moves the abrasive tool inchingly to make the robot memorize more exact 
position data as for a portion where the highest process accuracy is 
demanded, while he has given the memory instruction of the positional data 
in his own way whenever the robot's abrasive tool travels on the locus as 
for a portion where a generous tolerance is allowed. And, these 
instructions have all been given at the operator's optional discretion, so 
that the mental and physical burdens of the operator have been obliged to 
result in very serious problems. Especially, with regard to the "teaching" 
operation for a turnback point on the reciprocatingly travelling locus of 
the abrasive tool, scrupulous care has had to be taken on the proceeding 
of the grinding work. 
SUMMARY OF THE INVENTION 
It is therefore a principal object of the present invention to solve these 
drawbacks existing in the prior art and to provide an entirely new 
playback system grinding robot comprised of: a means for generating 
directional data to indicate a moving direction of the abrasive tool in 
addition to a means for generating positional data to indicate a position 
of the said abrasive tool, a means to memorize said data in accordance 
with a given period of sampling clock signal at the time of "teaching", 
especially to store the positional data pertaining to a turnback point on 
the abrasive tool travelling locus exactly when the directional data are 
changed and; designed to forcedly decelerate the abrasive tool movement 
according to the change of directional data in the case of "playback" work 
and to determine a process speed of the playback work according to the 
variation volumes of said stored positional data and directional data and 
to enable playback-working suited to the required process accuracy with a 
mere operation to move the abrasive tool along the locus learned at the 
time of "teaching". 
Generally, in the grinding work, when doing it consecutively and 
reciprocatingly many times for a grinding object, the processor concerned 
will probably encounter a hard problem, that a process texture difference 
is created on the workpiece surface in the boundary areas of the abrasive 
tool traveling route because it travels repeatedly only along the same 
locus. 
Although this seems to be solved by inputting the positional data of both 
sides of the main tool travelling locus at the time of the "teaching" 
operation, if the work is merely carried out to create a long and narrow 
belt-shaped grinding surface, the problem of a superficial difference 
being formed on the boundary areas of both sides of the locus will not be 
solved. To solve this problem, the processor has to carry out the work in 
accordance with a procedure learned by the "scrupulous teaching" as in the 
manual labor operation, but if so, the work will require much time and 
labor. As the result, a capacity of the memory device for storing 
positional data will have to be enlarged. 
It is therefore another object of the present invention to solve the 
aforementioned problems by an apparatise having a correcting direction 
indicating flag to change a status whenever the positional data are read 
out of the "position" table by scanning it a given chamber of times, and 
having a correction data register to store in advance a correction ratio 
or a correction volume pertaining to the positional data which are newly 
incorporated in the robot mechanism in addition to the conventional 
structures. The peripheral areas of the abrasive tool travelling locus 
which are indicated by the positional data accessed from a "position" 
table can be ground without creating any difference on the workpiece 
surface by adding a correction corresponding to the status of the 
aforesaid correcting direction indicating flag (i.e. a correction based on 
a given correction ratio or a given correction volume) to the positional 
data read out of the "position" table and further by creating a number of 
the abrasive tool travelling loca at random according to the positional 
data subsequent to the correction. it is also and object to provide an 
entirely new and unique playback system grinding robot which enables 
grinding both peripheral areas of the abrasive tool main travelling locus 
without enlarging the positional data storage capacity and without 
incurring the trouble of the "teaching" operation.

DETAILED DESCRIPTION OF THE INVENTION 
Initially, referring to FIGS. 1 and 2, overall drawings of the present 
equipment are shown therein. A bedplate (1) is provided with a tool drive 
mechanism (2) and a table on which a workpiece is positioned. The tool 
drive mechanism (2) is so designed that a case (5) attached in a freely 
slidable condition to a guide bar (4) standing on the bedplate (1) can 
ascend and descend by the operation of a handle (6), and the case (5) is 
provided with a first, No.1, arm (8) turning around a main axis (7) and a 
second No.2, arm (10) connected by means of a pivot (9) to a head of said 
No.1 arm (8), and a holder (11) to fix an abrasive tool (18) is attached 
to a head of said No.2 arm (10). Further, a link (14) is connected by 
means of a pair of pins (15) & (16) to a portion between an arm (13) for 
driving No.2 arm abent a revolution shaft (12) arranged adjacent to the 
said main axis (7) and No.2 arm (10) designed to be possible to fix the 
abrasive tool. Each turning motion of No.1 arm (8) and the arm (13) for 
driving No.2 arm is actuated by a resultant force composed by both of No.2 
arm (10) and link (14) and provides a horizontal movement for the abrasive 
tool (18) fixed to the holder (11). 
Referring then to FIGS. 3 and 4, a structure is shown to turn No.1 arm (8), 
which is built in the case (5) which can be seen therein. A revolution 
cylinder (21) extending upward from the case (5) is inserted in a freely 
rotatable condition into a holding cylinder (20) arranged in the case (5) 
and, No.1 arm (8) is monolithically attached to the upper portion of the 
said revolution cylinder (21). And, a bottom portion of the revolution 
cylinder (21) is connected to a central axis (39) through a differential 
gear system speed reducer (22). Further, a brake plate (23) is fixed to 
the said case (5) and a cylinder portion (38) extending down ward is 
supported in a freely rotatable condition by a holding cylinder (24) 
fitted to the case (5). The aforementioned central axis (39) is connected 
to an output axle (26) of a servomotor (25) attached to the bottom portion 
of the holding cylinder (24). 
The servomotor (25) is of a clockwise and counterclockwise rotatable type. 
Rotating now the servomotor (25), a revolutionary force of its output axle 
(26) will be decelerated through the speed reducer (22) and then 
transmitted to the revolution cylinder (21) and act to cause No.1 arm (8) 
as well as the said revolution cylinder (21) to turn around the main axis 
(7). 
The aforesaid revolution cylinder (21) is provided with a toothed disc 
(27), which is connected with a rotary encoder (28) built in the case (5) 
by means of a toothed belt (29). The rotary encoder (28) acts to detect a 
turning angle of No.1 arm (8) and at the same time causes the servomotor 
(25) to run clockwise and counterclockwise within the range of a given 
turning angle, thereby enabling No.1 arm (8) to turn reiteratively. 
The present invention will then be described as to a turning mechanism of 
the tool holder by reference to FIGS. 3 and 5. The aforesaid main axis (7) 
supports a root end of No.1 arm (8) and incorporates a toothed pulley (30) 
rotating inside the said No.1 arm (8), and a motor (31) is mounted on a 
portion projecting from No.1 arm (8) supported by the said main axis (7). 
Further, the aforesaid pivot (9) which is arranged at a connection part of 
No.1 arm (8) and No.2 arm (10) incorporates a pair of pulleys (32) and 
(33) which are rotated inside the respective arms and also another toothed 
pulley (35) is fitted to a revolution axis (34) of the holder (11) 
arranged at the head of No.2 arm (10). The aforementioned four (4) toothed 
pulleys (30), (32), (33) and (35) are each of an equidiameter and designed 
to transmit a revolutionary force of the motor (31) to the holder for 
attaching the abrasive tool (18) by arranging a toothed belt (36) between 
the pulleys (30) and (32) inside No.1 arm (8) as well as a toothed belt 
(37) between the pulleys (33) and (35) inside No.2 arm (10). In this case, 
the abrasive tool (18) is contrived to be possible to freely change its 
turning direction through the rotation of motor (31). 
By the way, the aforesaid revolution shaft (12) of the arm (13) for driving 
No.2 arm to reiteratively move the link (14) is supported rotatably by the 
case (5) and designed to be rotated clockwise and counterclockwise via a 
speed reducer, by the servomotor (4) arranged under the case (5). Although 
the said speed reducer is unillustrated here, its structure is identical 
with one connected to the foregoing revolution cylinder (21) and a brake 
plate (41) is fitted likewise thereto, and each brake plate (23) and (41) 
of the two is arranged in position at the same level. 
In addition to the above, a toothed disc (unillustrated) of the same type 
as one (27) fitted to the aforementioned revolution cylinder (21) is 
attached to the revolution shaft (12) and connected to another rotary 
encoder (42) arranged adjacent to the aforesaid rotary encoder (28) with a 
toothed belt (unillustrated). This rotary encoder (42) acts to detect a 
turning angle of the arm (13) for driving No.2 arm and to control the 
servomotor (40). 
In this connection, a force to press down the abrasive tool on the 
workpiece surface is contrived to be produced by an air cylinder (17) 
arranged on the tool holder (11) (this structure is unillustrated). 
The present invention will then be described as to an operational procedure 
of the robot. The present equipment is a playback system robot to carry on 
the grinding work according to the selfsame procedure as taught at the 
time of "teaching" that the operator inputs the contents of work into the 
memory device while gripping and moving the tool holder (11) along a 
profile of the workpiece. In this case the operator has to release the 
speed reducer (22) prior to proceed to the "teaching" in order to minimize 
a turning force of Nos.1 and 2 arms (8 & 10). After this, the operator has 
to put a series of information of the working procedure suited to a shape 
of the workpiece into the memory device. 
After completion of the "teaching" operation, a braking force is applied to 
the brake plates (23) and (41), and the grinding work can then soon be 
initiated. 
As can be understood from the above-noted explanation, the grinding work 
according to the present invention is effected by a mere operation to move 
the abrasive tool holder along a profile of the workpiece in the same way 
as taught at the time of "teaching". In that case, although the abrasive 
tool plays through a 3-dimensional movement at that time, the driving arm 
plays through only a horizontal movement, so that a control operation of 
the abrasive tool can completely be accomplished by only the positional 
data of the X-axis and Y-axis coordinates. This makes it possible to 
minimize the accessary memory device capacity, and to simplify an input 
program, and also to stabilize the playback work and further to improve an 
efficiency of the grinding work. 
Also, the abrasive tool (18) can be turned in direction through an angle of 
90 degrees by rotating a tool drive motor (31) shown in FIG. 3, so that 
the abrasive tool can turn its posture in an optional direction in 
accordance with the motion of the No.1 arm (8) and the No.2 arm (10) to 
move the tool (18). Moreover, if the work is carried out with the 
selection of a kind of tool, e.g. a tool suited for grinding work of the 
curved surface, a tool suited for grinding work of the plane surface, 
etc., its efficiency will be enhanced. Further, in the grinding robot 
under the present invention, the table device (3) fixing the workpiece 
thereon can freely be turned and inclined, the efficiency of the grinding 
work will drastically be heightened, thus providing a great deal of 
effects and advantages for users. 
Referring then to FIG. 6, an explanatory illustration of the arm motion of 
the playback robot according to the present invention is shown therein. As 
the present grinding robot has a dual degree-of-freedom in polar 
coordinates, a position of the abrasive tool is determined by both an 
angle .theta..sub.1 which is formed between No.1 arm (8) and a fiducial 
line as well as an angle .theta..sub.2 which is formed between a fiducial 
line and the arm (13) for driving No.2 arm (10). For this reason, the 
aforesaid rotary encoders (28) and (42) are respectively connected to the 
motor (25) to turn the No.1 arm (8) and to the motor (40) to turn the arm 
(13) for driving the No.2 arm, thereby making it possible to catch a 
position of the abrasive tool (18). An arm structure of the playback robot 
shown in FIG. 6 is designed to receive the "teaching" of the grinding work 
while gripping a handle (43) attached to a head (10a) of No.2 arm (10) and 
travelling the abrasive tool along a profile of the actual workpiece 
surface, while, in FIG. 1, the "teaching" operation is carried out by 
using the tool holder (11). In this case, the handle (43) is provided with 
a pair of direction sensors (48) and (49) in order to detect "which 
direction the abrasive tool (18) moves to". 
Referring to FIG. 7, one example of said direction sensors (48) and (49) 
attached to the handle (43) are illustrated therein, where an inner 
cylinder (44) is attached to a mandrel (44c) fixed at a head portion (10a) 
of No.2 arm (10) in a freely rotatable condition. A handle outer cylinder 
(45) is supported by means of a pair of coiled springs (46) and (47) 
around an external circumference of the inner cylinder (44), and a plus 
direction detector (48) as well as a minus direction detector (49) which 
are, for example, comprised of a microswitch, etc. are arranged around the 
outer circumference of said handle inner cylinder (44). Accordingly, if 
the operator moves the abrasive tool (18) to a direction shown with an 
arrow "A" while gripping the handle outer cylinder (45), the said plus 
direction detector (48) is pressed by both of the handle inner cylinder 
(44) and the handle outer cylinder (45) and turns to "ON", while the minus 
direction detector turns to "ON" if the abrasive tool is moved to a 
direction of "B". 
Incidentally, the work is more effectively performed if the plus and minus 
directions of the direction sensors are adjusted to coincide with the 
reciprocating movement direction of the abrasive tool. Accordingly, when 
the reciprocating movement direction of the tool is changed largely, it is 
preferable to rotate and adjust the inner cylinder (44) to make the tool 
moving direction coincide with the plus and minus directions of the 
sensors (48) and (49). 
Referring then to FIG. 8, a block diagram of the robot control circuit 
according to the present invention is shown therein. In FIG. 8, the 
numerals (57) and (58) show flip-flop mechanisms to store the robot's 
moving directions at the time of "teaching" and the flip-flop (57) is set 
when the plus direction detector (48) turns to "ON" and is set when the 
minus direction detector (49) turns to "ON". On the contrary, the 
flip-flop (58) is set when the minus direction detector (49) turns to "ON" 
and reset when the plus direction detector turns to "ON". Therefore, the 
flip-flop (57) is set, the handle (43) is moved to a direction shown with 
the arrow "A" and when the flip-flop (58) is set, the handle (43) is moved 
to a direction of "B". 
A numeric number (28) shows an encoder connected to the main axis (7) and 
likewise a numeric number (59) shows an UP-DOWN counter. The encoder (28) 
produces a pulse signal synchronously with the turning motion of No.1 arm 
(8) revolving around the main axis (7) and, the counter (59) acts to count 
up and down with this pulse signal. Therefore, a value counted by the 
counter (59) indicates the aforementioned angle .theta..sub.1 which is 
formed between No.1 arm (8) and the fiducial line. In this way, the 
encoder (28), as it is connected to the main axis (7), generates a 
count-up clock signal "UC" and a count-down clock signal "DC" in both of 
the cases where the No.1 arm is rotated due to a rotation of the motor 
(25) and also the No.1 arm (8) is rotated by moving the abrasive tool (18) 
at the time of "teaching", and causes a count motion of the counter to 
step forward. A value counted by the counter (59) at the time of 
"teaching" is used for indicating a location of a series of the points on 
the abrasive tool traveling locus, while a value counted by the counter 
(59) at the time of "playback" is put out as a feedback information signal 
to indicate an present position of the abrasive tool (18). 
Further, a numeric number (61) shows a motor drive unit to provide an 
excitation pattern for the motor (25) and to actuate it. Its structure and 
action are known by any person well versed in this art. 
Moreover, as the grinding robot according to the present invention shown in 
FIG. 6 has a dual degree-of-freedom of polar coordinates, an encoder (42), 
a motor (40), a counter (60) and a motor drive unit (62) are prepared for 
a count system of the 1st series to actuate the arm (13) for driving the 
No.2 arm, as shown in FIG. 8. A count system of the 2nd series is of the 
entirely same in structure as that of the 1st series, that such a 
redundant explanation may be omitted here, except as to a point pertaining 
to a motion of the arm (13) for driving the No.2 arm. 
And, these units are connected to the control system through an 
input-output interface (50). 
Although this type of control system is generally composed of a 
microcomputer in which a microprocessor (51) and memory elements are 
incorporated in the heart of the mechanism, the control system according 
to the present invention is comprised of a RAM-composed table (52) and a 
ROM-composed table (53). 
Referring to FIG. 9, an explanatory illustration of the "table" in the 
memory device is shown therein. An upper bit column of the table (52) is 
assigned for each output of the flip-flops (57, 58) and a lower bit column 
of the table (52) is assigned for each output of the counters (59, 60) and 
acts to store the abrasive tool position. 
FIG 10 shows the functional contents of the table (53); its axis of 
abscissas shows a period of playback and its axis of ordinates shows a 
moving volume of the abrasive tool at the period of "playback", and each 
oblique line shows a frequency of the excitation pattern's generation to 
be given to the motors (25) and (40). 
Incidentally, in FIG. 8, a numeric number (54) shows a sampling time marker 
generator to produce a sampling clock signal at the time of "teaching", 
and a numeric number (55) shows a playback time marker generator to 
generate a playback clock signal at the time of "playback", and likewise 
(56) shows a pointer to indicate an address of the table (52), and (DB) 
shows a data bus and (AB) shows an address bus respectively. 
The present invention will then be explained as to an aspect of action of 
the robot employed in the embodiment. 
FIG. 11 shows an operational flow chart at the time of "teaching". In this 
"teaching", thoughtful consideration is paid to enable the operator to 
obtain appropriate data suited to the required process accuracy without 
keeping close watch on the timing of a sampling operation fitted for the 
process accuracy required. 
Initially, let it be supposed that a start instruction of the "teaching" 
mode is now given to the robot. A microprocessor (51) will then act to set 
up "0" to a pointer (56) and to specify the No. "0" address in the table 
(52). Thereupon, gripping and moving the handle (43) to travel the 
abrasive tool (18) on an optional locus, the work will then be initiated. 
At this time, if the abrasive tool is moved to a direction shown by the 
arrow "A", a microswitch (48) will turn to "ON" and actuate to set the 
flip-flop (57), but if the abrasive tool (18) is moved to a direction "B", 
a microswitch (49) will turn to "ON" and actuate to set the flip-flop 
(58). 
And, if the abrasive tool is moved to a certain direction, No.1 arm (8) 
will start to turn centering around the main axis (7) with the motion of 
the abrasive tool and the arm (13) for driving the No.2 arm will also 
start to turn centering around the revolution shaft (12). When the 
aforementioned angle .theta..sub.1 becomes larger due to the turn of the 
No.1 arm (8), the encoder (28) will generate the count up clock signal 
"UC" and cause the counter (59) to count up. On the contrary, when the 
angle .theta..sub.1 becomes smaller, the encoder (28) will generate the 
count down clock signal "DC" and cause the counter (59) to count down. 
Therefore, a value counted by the counter (59) comes always to indicate a 
value of the angle .theta..sub.1. Further, when the angle .theta..sub.2 
becomes larger due to the turn of the arm (13) for driving the No.2 arm, 
the encoder (42) will produce the count up clock signal "UC" and cause the 
counter (60) to count up, while, if the angle .theta..sub.2 becomes 
smaller, the encoder (42) will produce the count down clock signal "DC" 
and cause the counter (60) to count down. Therefore, a value counted by 
the counter (60) comes always to indicate a value of the angle 
.theta..sub.2. 
Moreover, when the "teaching" mode actually starts the sampling time marker 
generator (54) will generate a given period of the sampling clock signal 
which is fed to the microprocessor (51). The microprocessor (51) will then 
read the data out of the input-output interface (50) synchronously with 
the emission of this sampling clock signal. Incidentally, a period of this 
sampling clock signal is beforehand registered in the sampling time marker 
generator (54). 
The mircroprocessor (51) also acts to monitor each status of the flip-flops 
(57, 58) and to catch any change which might be caused in moving 
directions of the abrasive tool (18). When the "teaching" operation is 
initiated, the flip-flops (57) and (58) will both be reset. But, if the 
operator moves the abrasive tool (18) to any direction, either of the 
flip-flops (57) or (58) will be set. Therefore, the microprocessor (51) 
will judge the tool moving direction to have been changed and hold the 
status datum of the flip-flip (57) or (58) and write it in a upper bit 
column of No. "0" address of the table (52). 
Although this status datum is shown in a flow chart of FIG. 11 to be stored 
whenever the status of the flip-flop (57) or (58) is changed, there is no 
objection in writing the status data of flip-flops (57) and (58) in the 
upper bit column of the table (52) one by one irrespective of the said 
status change. 
And, the microprocessor (51) acts to hold a value counted by the counters 
(59) and (60) successively two times synchronously with the timing at the 
time when the sampling time marker generator (54) produces a sampling 
clock signal and, if a value held at the 1st time accords with that of the 
2nd time, the microprocessor acts to write its value in an lower bit 
column of No."0" address of the table (52). 
In this way, the microprocessor acts to add a value of "1" to a pointer 
(56) whenever the sampling clock signal is generated and to repeat the 
foregoing actions likewise, and then to store both of the directional data 
and the positional data of No.1 arm (8) and the arm (13) for driving the 
No.2 arm respectively in the lower bit and the upper bit columns 
subsequent to No."1" address. This completes the "teaching" operation. 
As noted above, in the present embodiment, a sampling of the data is 
carried out synchronously with the emission of a certain period of 
sampling clock signal, so that the data stored in the lower bit column of 
each address of the table (52) is defined as each angle .theta..sub.1 and 
.theta..sub.2 of the No.1 arm (8) and the arm (13) for driving the No.2 
arm at the time of sampling, and also the variation volume of each angle 
.theta..sub.1 and .theta..sub.2 undergoing a change every period of 
sampling is defined as the respective angular velocities of the No.1 arm 
(8) and the arm(13) for driving the No.2 arm. 
Accordingly, in the case where the "teaching" operation is carried out by 
tracing the travelling locus of the abrasive tool (18), the operator will 
generally move the abrasive tool slowly and gently when it comes to such a 
portion that the process accuracy is strictly requested. Therefore, the 
variation volume of each angle .theta..sub.1 and .theta..sub.2 undergoing 
a change within a specified period, i.e. each angular velocity of No.1 arm 
(8) and the arm (13) for driving the No.2 arm will decrease. On the 
contrary, as the operator will move the abrasive tool relatively swiftly 
when it comes to such a portion that the process accuracy is not so 
strictly required, each angular velocity of No. the 1 arm (8) and the arm 
(13) for driving the No.2 arm will increase. 
Consequently, according to the present embodiment, if the operator moves 
the abrasive tool of the arm head by the most natural motion in viewpoint 
of the human engineering, he will be able to store the positional and 
directional data of the abrasive tool properly into the memory device 
without paying special attention to the timing of data memorization. 
Referring then to FIG. 12, an operational flow chart at the time of 
"playback" is illustrated therein, which shows that the grinding work 
according to the present invention is carried out with scrupulous 
consideration to make it possible to practice the playback work suited to 
the required process accuracy at a reasonable "playback" work speed. 
Before initiation of the "playback" work, the operator initially inputs the 
data pertaining to a period of the "playback" work and selects a playback 
mode from a control console. At this time, if the operator, for example, 
selects a value of 10 ms as a period of playback work, the aforementioned 
playback time marker time marker generator (55) emits a playback clock 
signal at a period of 10 ms and the microprocessor (51) acts to read its 
datum out of the table (52) every period of 10 ms, and puts out a signal 
to perform the playback work every said period. 
When the "playback" mode is initiated, the microprocessor (51) initially 
functions to read out the data of No. "0" address through No."n" address 
in the table (52) synchronously with the emission of the playback clock 
signal sent from the playback time marker generator (55). In this case, a 
value of "n" may optionally be set up. For example, let it be supposed 
that a value of "5" is selected for "n". The microprocessor (51) will then 
act to make a comparison between a value of upper bit column of No.5 
address and a value of upper bit column of No."0" address and to judge 
whether the moving direction of the abrasive tool (18) is changed or not. 
And, if the said moving direction is changed, the microprocessor (51) will 
give an instruction to the robot to enter into a forced deceleration, but 
when the said moving direction is unchanged, an instruction will be given 
to select a moving speed suited to the variation volume of the positional 
data. 
That is to say, the microprocessor (51) functions to subtract a value of 
the No."0" address from that of the No."1" address and to access the thus 
subtracted value to a "frequency" table (53) as an address datum. The 
instruction data for frequency (i.e., frequency for motor drive pulse 
signal) are beforehand stored in the said "frequency" table, as shown in 
FIG 10, and the microprocessor (51) functions to read a certain frequency 
corresponding to the variation volume of positional data out of the said 
"frequency" table and to give its frequency datum through an input-output 
interface (5) to the motor drive units (61, 62), which cause the 
excitation pattern of motors (25) and (40) to renew successively with the 
use of this indicated frequency. 
By the way, the variation volume per unit time of positional data is 
considerably large in such a portion that the operator moves the abrasive 
tool (18) swiftly, while it is relatively small in such a portion that he 
moves the tool slowly. However, since the "frequency" table (53) stores 
the instructed frequency corresponding to the variation volume per unit 
time of positional data, as shown in FIG. 10, a higher frequency will 
naturally be selected when the tool comes to a portion where the variation 
volume per unit time of positional data is large, while a lower frequency 
will be selected when the tool comes to a portion where the variation 
volume per unit time of positional data is small. 
For example, let it be supposed that the period of playback work is 10 ms 
and the variation volume of positional data is 8 or 10 pulses every period 
of sampling on the basis of output of the encoders (28, 42). A value of 
frequency "1 KHz" will then be selected and in consequence, if the 
variation volume is 16 or 20 pulses, the frequency value of 2 K Hz will be 
selected. 
Thus, the motor drive units (61, 62) act to renew the excitation pattern of 
the motors (25, 40) successively with the use of this instructed 
frequency, so that the abrasive tool (18) will be moved swiftly also at 
the time of playback work in the portion where the operator moved the 
abrasive tool (18) swiftly at the time of "teaching", and on the contrary, 
it will be moved gently also at the time of playback work in the portion 
where the operator moved the said tool gently at the time of "teaching". 
In this way, when the motors (25, 40) start to run and the No. 1 arm (8) as 
well as the arm (13) for driving the No.2 arm turn centering around the 
main axis (7) and the revolution shaft (12) respectively, the encoders 
(28) and (42) act to generate a count-up clock signal "UC" and a 
count-down clock signal "DC" and cause the counters (59, 60) to step 
forward according to these count-up clock signal and count-down clock 
signal. In the present embodiment, the microprocessor (51) is also 
contrived to make it possible to emit a feedback signal pertaining to the 
tool position in accordance with the optionally demultiplied to the 
playback period. 
To put it concretely, the microprocessor (51) acts to read each value 
counted by the counters (59, 60) in its mechanism as the data of present 
tool position through the input-output interface (50) according to a 
timing instructed within the period of "playback" and to subtract the thus 
read-in datum value from the datum value of the instructed tool position. 
For example, when the operator accesses some data from the "frequency" 
table on the basis of a difference between No."0" address and No."1" 
address in the table (52), a datum value of No. 1 address in the table 
(52) means an instructed tool position, so that an outcome subtracted a 
datum value of the present tool position will be obtained simply. The 
microprocessor (51) accesses said subtracted datum value to the 
"frequency" table (53) as the number of the address and provides an 
excitation clock signal with a frequency corresponding to a difference 
between the instructed position and the present position to the motors 
(61) and (62) respectively. In this way, when the instructed position 
accords with the present position, the address number in the table (52) 
will be renewed whenever the subsequent playback clock signal is given 
from the playback time marker generator (55), and the foregoing actions 
will be repeated likewise. 
Further, if the directional data are adversely changed in the course of 
execution of the playback work, the microprocessor (51) will enter into a 
forced deceleration mode as noted above. To put it concretely, when a 
numeric value "5" is selected as a value of the No."n" address, if a datum 
value in the lower bit column of the No."i" address of the table (52) is 
of an instructed position, the microprocessor (51) functions to make a 
comparison between a directional datum shown by a value in the upper bit 
column of the No."i+n" address of the table (52) and a positional datum as 
shown by a value in the upper bit column of the No."i" address of the 
same, and if the two discord with each other, the microprocessor acts to 
enter into a forced deceleration mode and to read the minimum frequency 
(e.g., 500 Hz in the table of FIG. 10) out of the "frequency" table (53) 
irrespective of the variation volume of the positional data at that time 
and to provide its datum value to the motor drive units (61), (62) 
respectively. Accordingly, the motors (25, 40) run each at the lowest 
speed, so that the abrasive tool also moves at the lowest speed. 
Incidentally, even in this forced deceleration mode, a routine for feedback 
of positional data is ready for use, so that the robot is possible to 
enter into subsequent work as soon as the present position accords with 
the instructed position. 
In the foregoing description, the encoders (28, 42), the counters (59, 60), 
the motors (25, 40) and the motor drive units (61, 62) have been explained 
without sectionalizing every item, however, it is needless to say that two 
series of motions of the No.1 arm and the No.2 arm are respectively 
possible to be actuated independently. 
As has been explained above, according to the present invention, the 
operator can input proper data of "playback" work suited to the required 
process accuracy into the memory device by doing a mere operation to trace 
the abrasive tool locus slowly in a portion where a fine motion, i.e. 
specific accuracy is required and swiftly in a portion where a generous 
motion may be allowed. Especially, the present robot is designed to make 
it possible to input the data of turnback point of the abrasive tool on 
the locus properly into the memory device by the function of the direction 
sensor. Accordingly, the operator becomes needless to pay special 
attention to the input timing of positional data, so that his physical and 
mental burdens will greatly be lightened. 
Moreover, according to the present invention, when a moving direction of 
the abrasive tool is changed, the present robot is designed to move the 
abrasive tool at the lowest speed, so that the grinding process itself is 
effectively protected from various troubles which may be caused due to 
overrun, etc. 
Further, the present robot is so contrived that the positional informations 
of the abrasive tool indicate an absolute location computed from the 
fiducial line. Therefore, even if the "playback" work is reiteratively 
carried out any number of times, there is no accumulation of error and, in 
consequence an exact playback work will always be assured. 
Incidentally, it may remarked that a kind of coordinate pertaining to the 
arm joint as well as the number of degrees of freedom degree are not 
specifically limited, though the foregoing description has mainly been 
made on the basis of a specific robot having a dual degree-of-freedom of 
the polar coordinates. 
FIG. 13 is a diagram showing the conventional robot's drawbacks which the 
present invention aims to solve. When giving an instruction to the 
abrasive tool (18) at the time "teaching" to reiteratively grind the 
workpiece along the points "a.sub.1 " to "a.sub.n " on the tool travelling 
route and putting the robot into grinding motion as per the "teaching", a 
facial difference is apt to be created on the peripheral areas of the said 
route. Thereupon, the present invention will then be described in further 
detail as to the grinding robot provided with a random correction flag 
device which removes the facial difference out of the workpiece surface to 
be ground by reference to FIGS. 14 and 15. 
FIG. 14 shows an operational block diagram of the grinding robot provided 
with a random correction flag device according to the present invention. A 
numeral (52) shows a RAM-composed position table to successively store the 
positional data, and likewise (63) shows an address counter to count a 
playback clock pulse "PC" and to renew an address in said position table 
(52), and the same (64) shows an address decoder to decode an output value 
of said address counter respectively. These units of "position" table 
(52), address counter (63) and address decoder are each known. The control 
circuit, fundamentally, acts to determine an excitation pattern to be 
excited according to the positional data sequentially read out of the 
position table (52) and to provide the thus decided excitation pattern to 
the motor drive units (61,62), which cause the motors (25, 40) to drive 
according to the given excitation pattern. 
A numeral (68) shows a correction data register to store the correction 
volume of the positional data, and said correction volume is preset by the 
operator in advance. And, a numeral (69) shows a frequency division 
circuit to generate a pulse signal if a carry-over output of the address 
counter (63) is impressed to the said circuit by the preset number of 
times, and an output of the frequency division circuit is impressed to a 
ring counter (70) which is possible to take a count value of either of "1" 
or "3". A numeral (71) shows a decoder to decode an output of the ring 
counter (70) and the same (72) shows a flag to indicate a correctional 
direction. Incidentally, the flag (72) is composed of a zero "0" 
correction flag (72a), a plus "+" correction flag (72b) and a minus "-" 
correction flag (72c). 
The present invention will now be described as for an aspect of the 
performance of the embodiment. 
Initially, referring to FIG. 15, a travelling locus of the abrasive tool 
(18) using a random correction flag device according to the present 
invention is illustrated therein. In the present embodiment, each 
positional datum of the abrasive tool on its travelling locus "AO" is 
sequentially inputted into the memory device at the time of "teaching" and 
stored in serial order in each address of the "position" table. At this 
time, ".alpha."-data to show a correction volume are stored in the 
correction data register(68) prior to initiate the "playback" work, and 
"i"-data to show "how many times the abrasive tool is to reiteratively 
grind the same locus" are preset in the frequency division circuit (69) 
before the "playback" work. 
By the way, the decoder (71), in an initial stage, indicates a zero "0" 
correction flag (72a) which is in "ON" state. 
When the "playback" mode is initiated, the playback clock signal "PC" will 
be impressed to the address counter (63), which is caused to step forward 
by this playback clock signal "PC". A value counted by the address counter 
(63) will then be sent to the address decoder (64). And, this address 
decoder (64) acts to decode this counted value and to specify an address 
read out of the "position" table, so that the positional data are 
sequentially read out of the No.1 address of the "position" table whenever 
the playback clock signal is emitted and the thus readout positional data 
are then sent to the control circuit (65). 
As noted above, in an initial stage, the zero "0" correction flag (72a) is 
in "ON" state, so that the control circuit (65) acts to determine the 
excitation pattern as per in the positional data read out of the 
"position" table (52) and the thus decided excitation pattern is sent to 
the motor drive units (61, 62), which cause the motors (25, 40) to drive 
according to this excitation pattern. The travelling route of the abrasive 
tool (18) is established on a series of points depending on the rotation 
of these motors (25,40). Thus, the abrasive tool (18) comes to travel on 
the locus "AO" shown by FIG. 15. 
In this way, when the abrasive tool (18) grinds the workpiece surface along 
the point "a.sub.1 " . . . "a.sub.n " while travelling on the locus "AO", 
the address counter (63) will carry over its count value. If so, the 
abrasive tool (18) will start to return on the locus just now travelled 
and the positional data will again be read out of the No.1 address of the 
"position" table (52) and the abrasive tool will repeat the foregoing 
action likewise. 
Thus, if the foregoing action is repeated by "i" times, the frequency 
division circuit (69) will generate its pulse signal at random and, the 
ring counter (70) will be caused to step forward by this pulse signal. The 
decoder (71) will then decode the value counted by said ring counter (70) 
and act to change a status of the flag (72) in the order of the zero "0" 
correction flag (72a).fwdarw.the plus "+" correction flag (72b).fwdarw.the 
zero "0" correction flag (72a).fwdarw.the minus "-" correction flag 
(72c).fwdarw.the zero "0" correction flag (72a). 
On the other hand, the positional data are sequentially given to the 
"position" table in serial the order of No.1 address through the No."n" 
address, and at the same time the correction data are also given thereto 
from the correction data register (68) while changing its datum with a 
flow of "0".fwdarw.".alpha.".fwdarw."0". 
When the plus "+" correction flag (12b) turns to "ON", the control circuit 
(65) acts to add the correction data "0".about.".alpha." sent from the 
correction data register (68) to the positional data read out of the 
"position" table (52) whenever the playback clock signal "PC" is emitted, 
and to compute and process the positional data after the correction was 
made and to decide the excitation pattern corresponding to the thus 
corrected positional data. Thus, the motor drive units (61, 62) drive the 
motors (25, 40) respectively according to the plus "+" corrected 
excitation pattern, so that the abrasive tool comes to grind to the extent 
of the peripheral areas of "A+.alpha.", as shown in FIG. 15, on the tool 
travelling locus while displacing the progress direction of the abrasive 
tool. 
On the other hand, when the correction flag (12c) turns to "ON", the 
control circuit (65) acts to subtract the correction data 
"0".about.".alpha." given by the correction data register (68) from the 
positional data sequentially read out of the "position" table (52) 
whenever the playback clock signal "PC" is emitted and to compute and 
process the positional data after the correction was made, and to decide 
the excitation pattern corresponding to the thus corrected positional 
data. And, the motor drive units (61, 62) drive the motors (25, 40) 
respectively according to the minus "-" corrected excitation pattern, so 
that the abrasive tool displaces its progress direction and carries out 
the grind work to the extent of peripheral areas of "A+.alpha." on the 
tool travelling locus, as shown in FIG. 15. 
In this way, when the abrasive tool (18) carries out the grinding work in 
zigzags by "i" times along the points "a.sub.1 " through "a.sub.n " on the 
locus while changing the progress direction of the tool indicated by the 
correction flag, the correction data value will then vary in such a way as 
"0".fwdarw.".alpha.".fwdarw."0", that is, its value returns again to he 
original one. Therefore, the whole system of the grinding robot returns to 
a state of linear movement in the initial stage, and the abrasive tool 
starts to grind again along the route of the locus "AO". 
In the foregoing embodiment, though the examples that the correction data 
of "0".fwdarw.".alpha.".fwdarw."0" are added to and subtracted from the 
status of flag (72) are shown, when doing such grinding work, these 
provide a random zigzag movements as far as practicable for the abrasive 
tool (18), to produce a fine work which is entirely free from facial 
differences. 
Also, it is needless to say that there is no objection in using the known 
"position feedback" and "speed feedback" devices jointly with the robot 
control system according to the present invention. Further, at the time of 
grinding work, if the pressure applied on the grinding object is 
relatively given strongly when the zero "0" correction flag is in "ON" 
state and softly when the plus "+" and minus "-" correction flags are in 
"ON", a factor to create the facial difference will be more reduced. 
As can be understood from the above explanation, according to the present 
invention, the peripheral areas of fiducial route of the abrasive tool can 
also be ground, so that no facial difference is created at a boundary area 
of the tool travelling locus; besides, it need not prolong the "teaching" 
time, nor require enlargement of the capacity of "position" table (52).