Teaching and playback method for work machine

A teaching and playback method for a work machine that is applicable to construction equipment such as a hydraulic excavator to automatize operation. Data on the operator's operation of work machine actuators is stored, and the stored data is reproduced so that the same operation as that by the operator is automatically performed. The method is adapted to effect exactly the same operation as what has been taught even when, during playback, the load on the actuators has varied from the level applied during the teaching. For this purpose, the pump discharge amount and the amounts of flow supplied to the actuators which are present during the teaching are stored. During playback, when the load has varied, and the pump discharge has changed, the engine output is controlled in such a manner that the actual pump discharge becomes equal to the amount stored during the teaching. When the flows supplied to the actuators have changed, the flow control valve provided in an inflow circuit is controlled in such a manner that the actual flows become equal to the amounts stored during the teaching. Thus, even when the load during playback has varied from the level during the teaching, the actuators can operate exactly as taught, without involving a discrepancy in the locus of operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a teaching and playback method for a work 
machine and, more particularly, to such a method capable of assuring that 
construction equipment such as a hydraulic excavator performs a playback 
operation exactly as has been taught, even when a variation has occurred 
in the load on the machine. The method thus enables the machine to operate 
with improved accuracy even in such an event. 
2. Description of the Related Art 
Recently, it has often been the case with construction machines that they 
are required to perform work by repeating a certain operation. This 
particularly applies to a hydraulic excavator which is required, by the 
nature of its work, to perform repeated operations during, for example, 
earth excavation or loading. On the other hand, automatization of 
construction machines has been propelled by recent development in 
electronics, as shown in, e.g., Japanese Patent Application No. 
149647/1988 (an application previously filed by the same applicant). A 
conventional teaching and playback method intended to automatize a 
construction machine of the above-described type has the following 
arrangement. During teaching, a locus of the work machine is taught by 
converting, into an electrical signal, the amount by which a work machine 
operation lever (hereinafter abbreviated to "work machine lever") is 
operated to move the machine along the locus, and storing the signal in a 
memory. During reproduction driving, the stored data is read from memory 
so that the machine performs a playback operation, which is an operation 
exactly the same as the taught operation. 
With the conventional method, however, the following problem may be 
encountered in the event that, during a playback operation, the load on 
the machine should vary from the level upon which the teachings have been 
formulated. When the load on the machine has varied, particularly when it 
has increased from the above-mentioned level, there is the risk that the 
engine output may fall short. The engine rotational speed drops, causing a 
corresponding drop in the pump discharge. The insufficient pump discharge 
causes the work machine to move along a locus different from what has been 
taught. Thus, the machine operates with degraded accuracy. If a load 
variation occurs during multiple-actuator operation in which a plurality 
of work machine actuators are operated, there is a risk that the amount of 
flow supplied to the actuators may change, also resulting in movement of 
the machine along a locus different from the taught locus, hence, in 
degraded accuracy of operation. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished with a view to overcoming the 
above-described problem. It is an object of the present invention to 
provide a teaching and playback method for a work machine that is capable 
of assuring that a playback operation is performed exactly as specified 
during teaching, even when, during the playback operation, the machine has 
encountered a variation in the load from the level applied during the 
teaching. 
In order to achieve the above-stated object, a teaching and playback method 
for a work machine according to the present invention comprises the steps 
of: effecting a teaching mode during teaching where an operation signal 
indicative of the operator's operation of a plurality of work machine 
actuators is stored, the mode being effected in such a manner as to store 
the pump discharge amount and the amounts of flow supplied to the 
actuators that are present during the teaching; effecting a playback mode 
in which the actuators are operated in accordance with the data stored 
during the teaching mode so that the actuators perform the same operation 
as that by the operator; and effecting a control mode in which, when a 
variation in the load has been detected during the playback mode, the 
output of the engine linked with the pump is controlled and the flows 
supplied to the individual actuators are adjusted in such a manner that 
the actual pump discharge and the actual flows supplied to the actuators 
become equal to the stored pump discharge amount and the stored actuator 
flow supply amounts, respectively. 
The method according to the invention is such that, even when, during 
playback, the load changes to become different from the level applied 
during the teaching, pump discharge compensation through the engine output 
control, as well as compensation for the flows supplied to the actuators, 
enables a playback operation to be performed exactly as specified by the 
teaching. The method thus overcomes the above-described problem. For this 
purpose, the actual engine output during teaching is reduced to a level of 
the order of 80% of the rated output, thereby providing a certain margin. 
When, during playback, the load has increased, the variation in the load 
causes a drop in the actual engine output and a corresponding drop in the 
pump discharge. According to the present invention, when the pump 
discharge has dropped, the actual engine output is automatically increased 
to maintain the pump discharge at the amount that was present during the 
teaching, thereby assuring that the same operation as specified by the 
teaching will be performed. If a variation in the load has occurred during 
multiple-actuator operation, the method uses a pressure compensated flow 
control valve disposed in an inflow circuit through which the actuators 
are supplied with flow. The valve is operated to adjust, i.e., increase or 
decrease, the flows supplied to the actuators in such a manner that the 
actual flows will become equal to the amounts that were present during the 
teaching, thereby assuring that exactly the same operation as the taught 
operation will be performed. 
Therefore, the method according to the present invention is capable of, in 
addition to various advantages inherent in a teaching and playback method, 
overcoming the problem conventionally encountered, i.e., a variation in 
the load causing a deviation in the playback movement, more specifically, 
a discrepancy in the locus of the work machine from that taught during 
teaching. The method overcomes the problem by maintaining, through engine 
output control, the pump discharge at a certain amount and by maintaining, 
through flow adjustment, the flows supplied to the actuators at certain 
amounts. Consequently, the operation during playback can be performed with 
improved accuracy. This is a great improvement in the automatization of 
work machines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Certain embodiments of the present invention will now be described with 
reference to the drawings. 
FIG. 1 shows a circuit for the teaching and playback control of a work 
machine (not shown), such as a hydraulic excavator, to which an embodiment 
of the present invention is applied. The control circuit includes a work 
machine lever 1, a device 2 for converting the operation amount of the 
work machine lever 1 into an electrical signal, an automatization 
controller 3, an electronic controller 4, a device 5 for controlling the 
amount of fuel injected into an engine 6, and a variable-displacement pump 
8 connected to the engine 6. The pump 8 has a regulator 7. An actuator 10, 
an electronic hydraulic valve 11 and a pressure compensated flow control 
valve 12 are connected to an inflow circuit 9 which is in turn connected 
to the pump 8. 
Although not shown, the hydraulic excavator has a plurality of work machine 
pump levers, and a plurality of actuators corresponding thereto. Since the 
levers or the actuators have the same construction, only one of the levers 
and the corresponding actuator are illustrated and will be described so as 
to avoid reader's confusion. 
The automatization controller 3 (hereinafter abbreviated to "AC") comprises 
an input interface 13, a circuit 14 for performing calculation and control 
on the basis of the signal inputted through the interface 13, a circuit 15 
for storing processing procedures, constants, etc., and an output 
interface 16 for outputting the values obtained by the calculation and 
control. During teaching, the AC 3 converts the work machine lever 
operation amount into an electric signal, stores the signal, and performs 
the necessary calculation. During playback, the AC 3 transmits the stored 
data to the electronic controller 4 by generating an output signal. 
The AC 3 is connected with switches 17, 18 and 19. The switch 17 is a mode 
changeover switch for changing from one of the manual mode (designated by 
OFF in FIG. 1), the automatic teaching mode (T), and the automatic 
playback mode (P), to another of these three modes. The switches 18 and 19 
are each a teaching or playback ON/OFF switch for starting and terminating 
a teaching or playback operation. 
The electronic controller 4 (hereinafter abbreviated to "EC") is connected, 
via signal circuits 20 and 21, with the electronic hydraulic valve 11. 
During playback, the EC 4 operates the valve 11 on the basis of the signal 
inputted from the AC 3 so as to control, through the actuator 10, a 
playback operation of the work machine. During playback, in order to cope 
with a variation in the load, the EC 4 receives feedback input signals and 
sends, on the basis of these input signals, command signals for the 
control of various members. For this purpose, the EC 4 is connected with 
the engine fuel injection control device 5 via input/output signal 
circuits 22 and 23, with the regulator 7 of the variable-displacement pump 
8 via input/output signal circuits 24 and 25, and with the pressure 
compensated flow control valve 12 via input/output signal circuits 26 and 
27. When a variation has occurred in the load during a playback operation, 
commands from the EC 4 cause the actual engine output and/or pump 
discharge to be controlled in proportion to a value indicative of the 
variation, so that the pump discharge will be maintained at the discharge 
amount that was present during the teaching. If a load variation has 
occurred during a multiple-actuator operation, the pressure compensated 
flow control valve 12 is controlled in a similar manner in proportion to a 
variation value, so that the flow supplied to the actuator 10 will be 
maintained at the flow supply amount that was present during the teaching. 
Specifically, the EC 4 stores signals outputted from the pump 8 and the 
flow control valve 12 during the teaching. When a change in the discharge 
of the pump 8, caused by a variation in the load on the actuator, has been 
detected, the EC 4 operates to output an engine rotational speed adjusting 
signal to the fuel injection control device 5 of the engine 6 which is 
directly connected to the pump 8, thereby performing control in such a 
manner that the discharge of the pump 8 will become equal to the discharge 
amount that was present during the teaching. On the other hand, there are 
a plurality of actuators 10, each associated with a flow control valve 12 
and an electronic hydraulic valve 11, which actuators 10 may be driven in 
a suitable combination thereof during a multiple-actuator operation. If 
such an operation is performed during playback, the actual flows which are 
present during the playback operation are compared with the flow amounts 
which were present during the teaching. The EC 4 performs control, with or 
without a variation in the load, in such a manner that the actual flows 
will become equal to the flow amounts during the teaching. 
The EC 4 has a construction similar to that of the above-described AC 3, 
and comprises an input interface 28, a control circuit 29 for performing 
calculation and control on the basis of the signal inputted through the 
interface 28, a circuit 30 for storing processing procedures, constants, 
etc., and an output interface 31 for outputting the values obtained by the 
calculation and control. 
The electronic hydraulic valve 11 is, as described above, used to control 
the operation of the actuator 10. A voltage indicative of the operation 
amount of the work machine lever 1 is inputted to the valve 11, and 
command currents are applied to two solenoids 32 and 33 of the valve 11, 
with the relationship of the command currents being calculated and 
controlled. The electronic hydraulic valve 11 may be substituted by 
electronic poppet valves 34a to 34d, as shown in FIG. 2. With this 
substitution, when signals expressing the command currents from the EC 4 
are inputted to two solenoids 35a and 35b, a meter-in poppet valve 34a and 
a meter-out poppet valve 34b open in response to and in accordance with 
the signals, whereby a command flow in accordance with the command 
currents is supplied to the actuator 10. 
Next, description will be given of the manner and procedure of operations 
performed by the teaching and playback control circuit. 
(1) Teaching Operation 
The teaching mode (T) is selected by switching the position of the mode 
changeover switch 17. Subsequently, the teaching switch 18 is turned on to 
start a teaching operation. When the work machine lever 1 is moved to the 
desired direction, the amount by which the lever is operated is inputted, 
as an electrical signal, to the AC 3, and is then stored therein. The 
electrical signal indicative of the lever operation amount is also 
inputted, through the EC 4, to the solenoids 32 and 33 of the electronic 
hydraulic valve 11. Through the control of the valve 11, the actuator 10 
is operated in such a manner that the work machine moves along a 
predetermined locus, the machine thus being taught. The teaching mode is 
terminated by turning off the switch 18. 
(2) Playback Operation 
Prior to the start of a playback operation, the posture of the work machine 
is set. Thereafter, the mode changeover switch 17 is operated to select 
the playback mode (P). Then, the playback switch 19 is turned on, thereby 
starting a playback operation. 
The playback operation is repeated until the playback switch 19 is turned 
off. When, during the playback, the load has varied from the level applied 
during the teaching, no special operation from the operator is required. 
Instead, the actual engine output is automatically controlled in such a 
manner as to maintain the pump discharge at the amount that was present 
during the teaching. When a load variation has occurred during a 
multiple-actuator operation, the pressure compensated flow control valve 
12 is adapted to adjust the flows in such a manner that they are 
maintained at the amounts that were present during the teaching. Thus, the 
playback can be performed exactly as specified by the teaching. 
When, during the playback, the operator operates the work machine lever 1, 
an additional signal is added to the AC 3 so that the electronic hydraulic 
valve 11 and the actuator 10 are operated in accordance with the 
additional signal as well. 
FIG. 3 shows a flowchart illustrating the teaching and playback control. 
The flowchart shows basic procedures for carrying out a teaching and 
playback method for a work machine according to the present invention. In 
Step S1, initial setting is performed. A determination is made, in Step 
S2, as to whether or not the current mode is an automatic mode. If the 
current mode is an automatic mode, it is determined, in Step S3, whether 
it is the teaching mode or the playback mode. 
If the current mode is the teaching mode, it is determined, in Step S4, 
whether or not the teaching switch is turned on, and, in Step S5, whether 
or not the playback switch is turned off. If affirmative answers are 
obtained in both of Steps S4 and S5, the memory of the electronic 
controller is cleared in Step S6. When a signal indicative of the 
operation of the work machine lever 1 has been inputted, the lever signal 
is stored (Step S7). The teaching mode is terminated when the teaching 
switch is turned off. 
On the other hand, if the current mode is the playback mode, determinations 
are made as to whether or not the playback switch is turned on (Step S8) 
and whether or not the teaching switch is turned off (Step S9). If 
affirmative answers were obtained in both of Steps S8 and S9, the data 
stored in a memory of the electronic controller is read (Step S10). In 
Step S11, on the basis of the memory data, a driving signal is outputted 
to the electronic hydraulic valve 11. In this step, if an additional 
signal indicative of the operation of the work machine lever 1 has been 
added, this signal is also outputted to the valve 11. When the reading of 
the memory data has been completed, the playback operation is completed 
(Step S12). 
INDUSTRIAL APPLICABILITY 
The teaching and playback method according to the present invention is 
applicable to construction equipment. The method can be particularly 
advantageously applied to the hydraulic drive apparatus of a hydraulic 
excavator. The method is applicable to a work machine of any type which 
has an hydraulic drive apparatus and which is required to perform repeated 
operations.