DEVICE & METHOD FOR CONTROLLING ATTACHMENT OF CONSTRUCTION MACHINE

TECHNICAL FIELD This invention relates to a control device and a control method for an attachment of a construction machine.

BACKGROUND

When performing straight-line excavation which uses a hydraulic shovel controlled by a hydraulic pilot operated control valve wherein tooth tips of a bucket are moved in a straight line semi-automatically or by some other way, a typical procedure which has been conventionally practiced calls for, as shown in Fig. 9, detecting the position of an attachment linkage by using a sensor attached to, for example, a joint of the attachment linkage and conduct closed loop control through a microcomputer. When the mode is switched between manual operation and automatic operation (the automatic straight excavation mode) in this case, a change valve of an on-off control action type is used in order to change pilot pressure which operates a main control valve for controlling a hydraulic cylinder.

In such a configuration, by setting the operating range of the attachment beforehand, the automatic mode is capable of preventing the equipment from advancing into the restricted operation area. Due to the configuration of the pilot pressure switching mechanism, however, it is difficult to include in the manual operation mode the function to limit the operating range of the attachment.

Therefore, when an operator is manually operating the attachment, he has to

take care not to accidentally hit the attachment against structures or objects around the machine. Even then, there still is the danger of such a collision damaging the construction machine itself and/or the other structure.

In order to solve the above problems, an object of the invention is to provide such a device and a method to control an attachment of a construction machine as to be capable of limiting and controlling the operating range of the attachment even during manual operation.

DISCLOSURE OF INVENTION A feature of the present invention comprises a construction machine attachment control device to control, using pilot operated main control valves, working fluid fed to hydraulic actuators that operate the attachment, the attachment control device having manual operation valves for manually controlling pilot pressure to be fed to the main control valves and electromagnetic proportional control valves which are disposed in the pilot pressure feed line for manual operation, somewhere between the respective manual operation valves to the aforementioned main control valves.

With the configuration as above, electromagnetic proportional control valves are provided inside the pilot lines from the manual operation valves to the aforementioned main control valves to feed pilot pressure during manual operation.

Therefore, when the attachment, during manual operation, approaches the area where the equipment is restricted to advance or in similar events, by means of the electromagnetic proportional control valves which electrically control manual operation pilot pressure, the device according to the invention is capable of adjusting the main control valves to the neutral position and thus thereby stopping the attachment, in accordance with electrical signals which are independent of the

operator's will. As the device is thus free from the danger of an operator's accidentally hitting the attachment against a building or other nearby objects during manual operation of the equipment, it ensures safe and easy manual operation.

Another feature of the invention comprises a construction machine attachment control device for controlling, using pilot operated main control valves, working fluid fed to hydraulic actuators that operate the attachment, wherein the attachment control device includes manual operation valves for manually controlling pilot pressure to be fed to the main control valves; an automatic-mode selecting valve for selecting other pilot pressure feed lines when the attachment is automatically operated, said other pilot lines being provided separately from the aforementioned pilot lines that pass through the manual operation valves; electromagnetic proportional control valves which proportionally open or close to a certain degree according to electric signals, thereby controlling pilot pressure fed from the manual operation valves or the automatic-mode selecting valve; electromagnetic change valves for selecting either the electromagnetic proportional control valves or the manual operation valves and outputting pilot pressures to the pilot chambers of the main control valves; a controller which controls the automatic-mode selecting valve, the electromagnetic proportional control valves and the electromagnetic change valves according to electric signals; attachment sensors which detect the distance moved by the attachment and input the information to the controller; and manual operation sensors which detect conditions of manual operation by the manual operation valves and input the information to the controller.

With the configuration as above, the invention provides a construction machine attachment control device which is capable of three functions, i. e. manual operation of the attachment; automatic operation of the attachment attained by an automatic-mode selecting valve to connect pilot pressure feed lines, which bypass the

manual operation valves, to electromagnetic proportional control valves; and control of the operation range of the attachment by means of the manual operation valves and electromagnetic proportional control valves. The greatest benefit of this feature of the invention lies in the operation range control mode wherein, by means of electromagnetic proportional control valves whose aperture is regulated according to electric signals from the controller so that pilot pressure supplied from manual operation valves is controlled independently of the operator's will, the attachment is automatically prevented from advancing into the restricted space. Further, even if one or more electromagnetic proportional control valves fail, manual operation is possible using a combination of valves comprising manual operation valves, electromagnetic proportional control valves and electromagnetic change valves, because pilot pressure from the manual operation valves can be fed through the electromagnetic change valves to the main control valves.

According to another feature of the invention, a shuttle valve is provided between each manual operation valve and the automatic-mode selecting valve so that said shuttle valve is capable of outputting pilot pressure fed from either valve to the corresponding electromagnetic proportional control valve. With the configuration as above, wherein a shuttle valve of a simple structure and low cost is used as a three-way valve between a manual operation valve, an automatic operation mode selecting valve and an electromagnetic proportional control valve, the overall configuration of the control circuit is simplified.

Another feature of the invention provides a construction machine attachment control method to control, using pilot operated main control valves, working fluid fed to hydraulic actuators which operate the attachment, wherein pilot pressure which is fed to manually operated main control valves is reduced when the attachment approaches a restricted operation area, and the pilot pressure to the main control

valves is completely blocked when the attachment has reached the restricted operation area, returning the main control valves to the respective neutral positions.

With the configuration as above, when the attachment approaches the restricted operation area, pilot pressure which is fed to manually controlled main control valves is reduced, the main control valves starting to return to the neutral positions. As a result, inertial load of the attachment is gradually braked by gradual shifting of the main control valves to the neutral positions. Therefore, when the attachment reaches the aforementioned restricted operation area, the control method according to the invention is capable of smoothly stopping the attachment, thereby preventing vibration or other hazardous effects of the shock caused by the halting of the attachment.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a hydraulic circuit diagram of an attachment control device of a construction machine according to an embodiment of the present invention; Fig. 2

(A) is a hydraulic circuit diagram showing a state of the circuit of said attachment control device during automatic straight excavation; Fig. 2 (B) is a hydraulic circuit diagram showing a state of the circuit of same when controlling the limit of the operating range; Fig. 3 is a system configuration of a hydraulic shovel equipped with said control device; Fig. 4 is an electric/hydraulic circuit diagram showing an overall system configuration of said control device; Fig. 5 (A) is an explanatory drawing illustrating the straight line bucket tooth tip excavation mode controlled by said control device; Fig. 5 (B) is an explanatory drawing illustrating the operation in cases where the function for maintaining the angle of the bucket is added to said straight line excavation mode; Fig. 6 is an explanatory drawing illustrating control of the height and the depth of the attachment by said control device during manual

operation; Fig. 7 is an explanatory drawing illustrating control of the reach of the attachment by said control device during manual operation; Fig. 8 is a flow chart showing a control method of said control device; and Fig. 9 is a circuit diagram of a conventional attachment control device.

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention is explained in detail hereunder, referring to a hydraulic shovel shown in Figs. 1 to 8 according to an embodiment of the invention. Fig. 3 is a system configuration of a hydraulic shovel equipped with a control device for controlling the attachment of a construction machine according to the invention, wherein the hydraulic shovel is provided with a lower structure 1 1 and an upper structure 12, which is mounted on lower structure 1 1 and has a front attachment 13.

Attachment 13 is provided with a boom 15bm, a stick 15st and a bucket 15bk, boom 15bm being rotated by a boom cylinder 14bm and supported at its base end by upper structure 12 through a shaft, stick 15st being rotated by a stick cylinder 14st and the vicinity of its base end being joined to the front end of boom 15bm and supported thereby through a shaft, and bucket 15bk being pivoted by a bucket cylinder 14bk and joined to the front end of stick 15st through a shaft, thus supported by stick 15st. Boom cylinder 14bm, stick cylinder 14st and bucket cylinder 14bk are hydraulic actuators that operate attachment 13.

Rotation angles of boom 15bm, stick 15st and bucket 15bk are respectively detected by angle sensors 16bm, lost and 16bk, which may be resolvers used as attachment sensors or any other suitable means. Signals representing detected angles are input through a signal transformer 17 mounted on upper structure 12 into a controller 21. Controller 21 includes a microcomputer.

Connected to controller 21 is a display switch panel 22 which serves as an input/output device, and members connected to the input terminal of the controller include a push-button type control switch 23, an engine pump controller 24, numerous pressure sensors 25 and an inclination sensor 26. Control switch 23 is mounted on an operation lever or other suitable member and serves to initiate automatic control or control the engine speed; engine pump controller 24 controls an engine and a pump based on the engine speed detected by an engine speed sensor 24a; pressure sensors 25 detect pressure of hydraulic circuits for driving attachment 13; and inclination sensor 26 detects an angle of inclination of the vehicle. Further, numerous electromagnetic valves, such as electromagnetic proportional control valves, electromagnetic change valves and so on, are connected to the output terminal of controller 21.

Fig. 4 is a block diagram of an entire system of said attachment control device, wherein input lines for various detected signals and output lines for outputting signals for driving electromagnetic valves are connected to controller 21, which is provided with tin external terminal 28 and a power circuit 29.

In Fig. 4, solid lines and dot lines respectively represent electric circuits and hydraulic pressure circuits. Long broken lines and short broken lines respectively represent a main hydraulic pressure circuit for driving the cylinders and a pilot pressure circuit. Drain circuits are omitted.

The main hydraulic pressure circuit comprises a supply circuit for feeding hydraulic fluid from a first main pump 32a or a second main pump 32b, both of which are driven by a vehicle engine 31, to the aforementioned boom cylinder 14bm, stick cylinder 14st and bucket cylinder 14bk, wherein such pilot operated valves as a main control valve 33bm for the boom, a main control valve 33st for the stick and a main control valve 33bk for the bucket are provided in the circuit.

As boom cylinder 14bm and stick cylinder 14st require a high flow rate, the circuits for feeding hydraulic fluid to boom cylinder 14bm and stick cylinder 14st are respectively provided with converging electromagnetic proportional control valves

34bm and 34st in order to converge fluid discharged from first and second main pumps 32a and 32b according to required flow rate.

The aforementioned pilot pressure circuit is provided with a pilot pump 41 which is driven together with main pumps 32a and 32b by vehicle engine 31. Manual operation valves 44bm, 44st and 44bk, which are proportional control valves for controlling output pressure of pilot pump 41, are connected to an output line 42 of the pilot pump, control of output pressure of the pilot pump being conducted through manual operation of respective operation levers 43bm, 43st and 43bk for the boom, the stick and the bucket.

An automatic-mode selecting valve 46 for bypassing manual operation valves 44bm/44st/44bk in control of the aforementioned output pressure of the pilot pump is connected to an output line 45 which branches off from output line 42 of pilot pump

41.

Shuttle valves 47bm, 47st and 47bk are provided between the respective output lines of manual operation valves 44bm/44st/44bk and the output line of automatic-mode selecting valve 46, and electromagnetic proportional control valves 48bm/48st/48bk for controlling, in accordance with electrical signals, pilot pressure from either manual operation valves 44bm/44st/44bk or automatic-mode selecting valve 46 are connected to the respective output lines of shuttle valves 47bm/47st/47bk.

Respectively connected to the output lines of electromagnetic proportional control valves 48bm/48st/48bk and the output lines of manual operation valves

44bm/44st/44bk are electromagnetic change valves 49bm/49st/49bk in order to select

either electromagnetic proportional control valves 48bm/48st/48bk or manual operation valves 44bm/44st/44bk and output the pressure to the respective pilot chamber of main control valves 33bm/33st/33bk.

Automatic-mode selecting valve 46, electromagnetic proportional control valves 48bm/48st/48bk and electromagnetic change valves 49bm/49st/49bk described above are electromagnetic-operated spool valves, whose spool positions are controlled based on electrical signals which are output by controller 21.

The aforementioned angle sensors 16bm/16st/16bk for detecting distance moved, i. e. angle of rotation, of the respective joints of attachment 13 are connected through signal transformer 17 to input terminals of controller 21. Also connected to input terminals of controller 21 are pressure switches 36bm/36st/36bk. as well as pressure sensors 25bm/25st/25bk, which serve as manual operation sensors to detect conditions of manual operation through the output lines of manual operation valves 44bm/44st/44bk. Pressure sensors 25bm/25st/25bk detect analog quantity of changes of manual operation valves 44bm/44st/44bk, while pressure switches 36bm/36st/36bk detect on-off changes of manual operation valves 44bm/44st/44bk.

Fig. 1 is an enlarged view of one of the hydraulic cylinder control circuits of the attachment control device shown in Fig. 4. In Fig. l,the elements corresponding to those in Fig. 4 are identified with the same reference numerals, but the elements on the cylinder-extended circuit are provided with the letter "a" and those on the cylinder-contracted circuit with the letter "b".

Referring to Fig. 1, connected to output line 42 of pilot pump 41 are a pair of manual operation valves 44a/44b which control output pressure of the pilot pump by means of proportional reduction of the pressure through manual operation of operation lever 43.

Automatic-mode selecting valve 46 for bypassing manual operation valves 44a/44b in control of the aforementioned output pressure of the pilot pump is connected to output line 45 which branches off from output line 42 of pilot pump 41. Said selecting valve 46 is an electromagnetic change valve. Shuttle valves 47a/47b are provided between the respective output lines of manual operation valves 44a/44b and the output line of automatic-mode selecting valve 46. Electromagnetic proportional control valves 48a/48b for controlling, in accordance with electrical signals from controller 21, pilot pressure from either manual operation valves 44a/44b or automatic-mode selecting valve 46 are connected to the respective output lines of shuttle valves 47a 47b. Proportional control valves 48a/48b are both electromagnetic proportioning pressure reduction valves.

Electromagnetic change valves 49a/49b of an on/off operation type are respectively connected to the output lines of electromagnetic proportional control valves 48a/48b and the output lines of manual operation valves 44a/44b. These electromagnetic change valves serve to select either type of valves and outputting the pressure to respective pilot chambers 33 a/33 b of main control valve 33.

Main control valve 33 has such a configuration that when pilot pressure is applied to neither pilot chamber 33a nor 33b, the spool of the main valve is returned to the neutral position by return springs which are disposed at both sides of the spool.

Angle sensor 16, which detects a rotation angle of a joint of the attachment, and pressure sensors 25a/25b, which detect pilot pressure through the output lines of manual operation valves 44a/44b, are connected to input terminals of controller 21 , while output terminals of controller 21 are connected to respective solenoids of the aforementioned automatic-mode selecting valve 46, electromagnetic proportional control valves 48a/48b and electromagnetic change valves 49a/49b.

Next, the function of the circuit shown in Fig. 1 is explained hereunder, referring to Figs. 1 and 2.

Fig. 1 shows the state of the hydraulic circuit in the normal manual operation mode, wherein all the electromagnetic valves (valves 46, 48a, 48b, 49a and 49b) are off in a nonconductive state. Therefore, pilot pressure which has been output from manual operation valve 44a or 44b according to the degree by which operation lever 43 has been operated is applied through electromagnetic change valve 49a or 49b to pilot chamber 33a or 33b of main control valve 33, and working fluid from main pump 32 is fed through main control valve 33, which is opened to the degree corresponding to the aforementioned pilot pressure, to head side 14a or rod side 14b of hydraulic cylinder 14 so that hydraulic cylinder 14 extends or contracts.

Fig. 2 (A) shows the state of the hydraulic circuit under the straight line excavation mode wherein, as shown in Fig. 5 (A), bucket 15bk is automatically moved in the process of excavation with the teeth of the bucket moving in a straight line, and the automatic excavation mode shown in Fig. 5 (B), which is capable of straight line excavation combined with a function to maintain the bucket at a constant angle.

As shown in Fig. 2 (A), while automatic excavation is performed, automatic- mode selecting valve 46 and electromagnetic change valves 49a/49b are all on in a conductive state, and, according to the degree of aperture of its spool in response to signals output from controller 21, electromagnetic proportional control valve 48a or 48b controls pilot pressure, which has been fed from automatic-mode selecting valve 46 through shuttle valve 47a or 47b. As a result, orientation and degree of aperture of the spool of main control valve 33 are controlled through electromagnetic change valve 49a or 49b. At that time, as operation lever 43 is at the neutral position, no pilot pressure is output from either manual operation valve 44a or 44b.

Fig. 2 (B) shows the state of the hydraulic circuit in cases where the working range of attachment 13 is limited in the manual operation mode. More precisely, it illustrates the hydraulic circuit in a case shown in Fig. 6 where the maximum height and digging depth of attachment 13 are limited when working in a tunnel or other similar environment, or a case shown in Fig. 7 where the length of the reach of attachment 13 with respect to a nearby wall is limited.

As shown in Fig. 2 (B), during the operation range control mode to limit the operation range of the attachment, automatic-mode selecting valve 46 is in a nonconductive state, while electromagnetic change valves 49a/49b are in a conductive state. In this state, according to the degree of aperture of its spool in response to signals output from controller 21, electromagnetic proportional control valve 48a or 48b controls manual operation pilot pressure, which has been fed from manual operation valve 44a or 44b through shuttle valve 47a or 47b. As a result, orientation and degree of aperture of the spool of main control valve 33 are controlled through electromagnetic change valve 49a or 49b.

At that time, in cases where the spool of main control valve 33 has been displaced due to, for example, pilot pressure supplied from manual operation valve 44a to pilot chamber 33a of main control valve 33, when the working range of the equipment is controlled, the pressure in pilot room 33a is reduced by means of reducing electric signals from controller 21 to the solenoid of electromagnetic proportional control valve 48a so that the springs are returned as shown in Fig. 1. As a result, the spool of main control valve 33 is returned to the neutral position, and the attachment stops.

Should either or both electromagnetic proportional control valves 48a/48b fail during automatic excavation shown in Fig. 2 (A) or operation with the limited attachment operation range shown in Fig. 2 (B), operation of the equipment can be

continued manually by using a combination of valves comprising manual operation valves 44a/44b, electromagnetic proportional control valves 48a/48b and electromagnetic change valves 49a/49b so that pilot pressure can be fed from manual operation valves 44a/44b through electromagnetic change valves 49a/49b to main control valve 33. In cases where even all the electromagnetic valves are in the non¬ conductive state at that time, the circuit according to the present embodiment has such a configuration that the springs of the valves are at the returned position so as to permit manual operation.

Fig. 8 is a flow chart of the procedure to control the lowering operation of boom 15bm when the lowest position of attachment 13 is limited as shown in Fig. 6.

Referring to the circuit diagram shown in Fig. 4 and the flow chart in Fig. 8, an example of the procedures to limit the lowering of boom 15bm is explained hereunder.

First of all, turn on (open) electromagnetic change valve 49bm while fully

opening electromagnetic proportional control valve 48bm (Step φ). and judgement is made based on signals from pressure sensor 25bm as to whether the operation is to

lower boom 15bm by means of manual operation valve 44bm (Step (2)). If the operation is to lower the boom, another judgement is made as to whether the tooth tips of bucket 15bk is closed to the predetermined boundary to which operation of

attachment 13 is limited (hereinafter referred to as the operation boundary) (Step (3))

For that purpose, the location of the tooth tips of bucket 15bk is constantly monitored by means of respective rotation angles of boom 15bm, stick 15st and bucket 15bk detected by angle sensors 16bm/16st/16bk which are resolvers or other suitable devices. When the tooth tips of the bucket come close to the operation boundary,

electromagnetic proportional control valve 48bm is slightly closed by control current

from controller 21 (Step ©), so that pilot pressure fed from manual operation valve

44bm through electromagnetic proportional control valve 48bm and electromagnetic change valve 49bm on the boom-lowering side into the pilot chamber on the boom- lowering side of main control valve 33bm is reduced, thereby moving the spool of main control valve 33bm to the neutral position. As the quantity of working fluid fed from main control valve 33 to the rod-side of boom cylinder 14bm is reduced as above, contraction of boom cylinder 14bm becomes slower, which slows down the lowering of boom 15bm. The control steps described above are repeated until the tooth tips of the bucket reach the operation boundary. Thus, by means of gradually narrowing the aperture of the spool of electromagnetic proportional control valve 48bm, the downward movement of boom 15bm is controlled to gradually slow down.

During the above control operation, whether the tooth tips of the bucket have reached the operation boundary is constantly surveyed (Step (D), and when the tooth tips have reached the operation boundary, electromagnetic proportional control valve

48bm is completely closed (Step ©), thereby completely eliminating the pilot pressure applied to the pilot chamber at the boom-lowering side of main boom control valve 33bm. As main control valve 33 is consequently returned by the springs to the neutral position, the lowering of boom 15bm is stopped.

Although the control procedure is explained as above referring to the control method to stop boom 15bm at the lowest limit in the lowering operation of the boom, the similar steps are applicable to cases such as when stopping boom 15bm at the highest limit in the elevation of the boom, stopping stick 15st at the inner or outer boundary during rotation of stick 15st and stopping bucket 15bk at the boundary

during its opening or closing operation.

INDUSTRIAL APPLICABILITY

As described above, even when a construction machine, such as a hydraulic shovel and so on. is being manually operated, a device and a method to control the attachment of a construction machine according to the present invention automatically control the working range of the attachment, thereby preventing the machine as well as a building and other objects near the machine from being damaged due to possible carelessness of the operator. Therefore, the control device and method according to the invention are suitable to such cases that require operating such a construction machine as a hydraulic shovel, a loader, a back hoe and so forth at a small site which allows only a minimal working space.