METHOD OF CONTROLLING BUCKET ANGLE OF HYDRAULIC SHOVEL

Abstract: A bucket-angle controlling method which is capable of automatically turning off the bucket-angle-maintaining control to maintain the bucket of a hydraulic shovel (12) at a specified position. When the open surface of the bucket (15bk) comes close to the horizontal plane, bucket angle ( theta bk), which is an angle of the bucket (15bk) open surface with respect to the horizontal plane, is maintained constant in order to prevent load from being spilled at the time of unloading and so forth. When bucket angle ( theta bk) is greater than a preset standard value ( theta bkset), a controller judges that bucket (15bk) is performing excavation. Then, the bucket-angle-maintaining control is temporarily deactivated to permit excavation to be performed through manual control.

Description: DESCRIPTION METHOD OF CONTROLLING BUCKET ANGLE OF HYDRAULIC SHOVEL TECHNICAL FIELD This invention relates to a method of controlling an angle of the bucket of a hydraulic shovel. BACKGROUND Fig. 4 (a) shows a manner of operation to maintain the bucket of a hydraulic shovel at a constant angle, wherein the position of bucket bk is automatically controlled in such a manner that the angle of bucket bk is constant while the open end of the bucket is kept approximately horizontal. With the angle of the bucket thus maintained, when unloading onto a dump truck or other receptacle/disposal place, the bucket can be automatically maintained, without having to operate an operation lever, at such a position as to be free from the danger of spilling the load. Fig. 4 (b) shows a manner of the automatic return operation, i. e. operation to return the bucket to the initial angle. The aforementioned bucket-angle-maintaining control also functions when excavation is performed in this condition. In order to perform digging, however, the bucket has to be manually operated by using an operation lever to shovel the load therein, which requires the equipment to be released from the bucket-angle-maintaining control. Should an operator of the equipment be forced to perform this switching operation for each action, it is very troublesome for him and may hinder effective use of the bucket-angle-maintaining control mode. In order to solve the above problems, an object of the invention is to provide a method of controlling an angle of the bucket of a hydraulic shovel, wherein the bucket-angle-maintaining control mode can be automatically deactivated. DISCLOSURE OF INVENTION The present invention comprises a bucket-angle-control method which involves bucket angle control to maintain the bucket of a hydraulic shovel at a constant angle, wherein the bucket-angle-maintaining control mode can be automatically turned off temporarily at times when excavation is detected to be taking place. With the configuration as above, even while the equipment is under bucket-angle-maintaining control so as not to spill the load, the bucket can be automatically released from this control whenever proceeding into the digging step, thereby permitting manual excavation in the same manner as conventional hydraulic shovels. At the time of unloading, the bucket is controlled in the normal bucket- angle-maintaining control mode at such a position as to prevent the load from spilling. According to another feature of the invention, the equipment is judged to be performing excavation in cases where the angle of the open surface of the bucket with respect to the horizontal plane exceeds a specified value. More precisely, the method calls for holding the bucket at a constant angle when the open surface of the bucket approaches the horizontal plane, and at all other times, assuming that the bucket is performing excavation, automatically switching the mode from the bucket- angle-maintaining control to manual operation. As this method is quite simple as a means of detecting excavation taking place, it can be easily handled by a control system. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is an explanatory drawing which illustrates an example of an action governed by a method of controlling an angle of a bucket of a hydraulic shovel according to the invention; Fig. 2 is a flow chart of an embodiment of said bucket- angle-control method; Fig. 3 is a system configuration diagram of a hydraulic shovel using same; Fig. 4 (a) is an explanatory drawing which illustrates the action of a hydraulic shovel when its bucket is controlled at a constant angle; and Fig. 4 (b) is an explanatory drawing which illustrates the action of same at the time of automatic return operation. BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention is explained in detail, referring an embodiment thereof shown in Figs. 1 to 3. 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 switch 23, an engine pump controller 24, numerous pressure sensors 25 and an inclination sensor 26. Switch 23 is mounted on the operation lever of attachment 13 or other suitable location; 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. Based on signals representing respective rotation angles of boom 15bm, stick 15 st and bucket 15bk which have been detected by angle sensors 16bm/16st/16bk. controller 21 is capable of constantly monitoring bucket angle ΘJpk, which is, as shown in Fig. 1. an angle of the bucket open surface with respect to the horizontal plane. Therefore, by means of electrically controlling one of electromagnetic valves 27 so as to control pilot pressure of pilot-operated control valves which extend and contract bucket cylinder 14bk. it is possible to keep the bucket at such a specified position as to prevent its load from spilling with bucket angle θ bk being maintained at a specified angle including 0°. Thus, the present embodiment has the bucket- angle-maintaining function such that when earth, sand or other materials are unloaded onto a dump truck, the bucket is maintained, without operating the bucket operation lever, at such a position as to prevent its load from spilling. Fig. 1 shows excavation mode A which calls for securing bucket cylinder 14bk of a hydraulic shovel so that bucket 15bk is affixed to stick 15st, and bucket- angle-maintaining mode B which calls for holding the bucket at such a specified position as to prevent its load from spilling when unloading the load in the bucket onto, for example, a dump truck. In excavation mode A, having detected that excavation is underway, controller 21 automatically deactivates the bucket-angle-maintaining function for the time being, thereby enabling manual operation. Conditions of the excavation work then are that stick 15st is drawn in (stick-in action) and that bucket angle θ bk with respect to the horizontal plane is greater than a specified standard value θ bkset. In other words, in cases where these conditions are present (presence of stick-in action and θ bk> θ bkset). the controller judges that the excavation is underway. Presence of the aforementioned stick-in action can be judged from angular speed (positive or negative) of stick 15st which can be detected according to the direction of inclination of the stick operation lever or angle sensor 16st. Further, as an example of measures, bucket side angle θ bkside may be used as said specified standard value θ bkset. Except when the above condition A (presence of stick-in action and θ bk> θ bkset) is satisfied, control of the aforementioned bucket-angle-maintaining mode B is conducted, wherein pilot pressure of the bucket cylinder control valves is automatically controlled by means of electromagnetic valves while, as described above, bucket angle θ bk is monitored by angle sensors 16bm/16st/16bk. As the bucket-angle-maintaining function thus controls extension and contraction of bucket cylinder 14bk in such a way as to maintain the bucket at specified angle θ bk, the bucket is prevented from spilling its load when unloading it onto a damp truck or in other occasions. Fig. 2 is a flow chart of the bucket-angle-maintaining control. When the bucket-angle-maintaining control is initiated, judgment is made as to whether stick-in action is underway, i. e. whether stick 15st is drawn in, during excavation operation (Step φ); and in cases where the movement of the equipment is stick-in action ("YES" in Step ®), judgment is made as to whether bucket angle θ bk is smaller than bucket side angle θ bkside, which serves as the specified standard value (Step (2)). In cases where bucket angle θ bk is greater ("NO" in Step (2)), which means θ bk> θ bkside during stick-in action, controller 21 judges that digging action is underway. Therefore, even if the equipment is in the bucket- angle-maintaining mode, controller 21 automatically deactivates the function for maintaining the bucket-angle, permitting stick 15st and bucket 15bk to be manually operated by means of the operation levers to continue the excavation (Step (_)). In cases other than the above ("YES" in Step ®). the system returns to the normal bucket-angle-maintaining control (Step ®). Then, bucket 15bk is lifted for the intended operation such as unloading with bucket angle θ bk being maintained constant. In cases where it has been judged in Step φ that the stick is not performing "stick-in action" ("NO" in Step φ ), the bucket-angle-maintaining control is performed as in Step ®, because it is obvious that the equipment is not performing excavation action. Further, according to the invention as claimed in claim 2. the system judges that excavation action is underway when bucket angle θ bk exceeds a specified standard value. However, means of detecting when excavation is taking place referred to in claim 1 is not limited to the degree of bucket angle θ bk. In other words, the invention as claimed in claim 1 includes, for example, a method which calls for attaching a pressure sensor to stick cylinder 14st and detecting pressure on the head-side of the stick cylinder to judge whether excavation is underway based on the fact that when excavation is being performed the digging load makes pressure on the head-side of stick cylinder 14st greater than the specified standard value. INDUSTRIAL APPLICABILITY As described above, a method of controlling an angle of the bucket of a hydraulic shovel according to the present invention is suitable for smoothly performing excavation and transporting load, such as the excavated earth, onto a transportation vehicle.

Claims: θ CLAIMS 1. A bucket-angle-control method which involves bucket-angle-control to maintain the bucket of a hydraulic shovel at a constant angle, wherein the bucket- angle-maintaining control mode can be automatically turned off temporarily by using a means of detecting when excavation is taking place. 2. A bucket-angle-control method as claimed in claim 1 wherein the equipment is judged to be performing excavation in cases where the angle of the open surface of the bucket with respect to the horizontal plane exceeds a specified value.

Inventors: ONO TOMOAKI, TOZAWA SHOJI, ONO, TOMOAKI, TOZAWA, SHOJI
Applicants: CATERPILLAR MITSUBISHI LTD, ONO TOMOAKI, TOZAWA SHOJI, ONO, TOMOAKI, SHIN CATERPILLAR MITSUBISHI LTD., TOZAWA, SHOJI
Application year: 1995
Main classification: E02F3
IPC codes: E02F3