Method and apparatus for controlling drilling operation

Abstract: In drilling control method and apparatus for making holes through a composite workpiece (3) made of a plurality of materials (3a, 3b) having different machining properties, the workpiece (3) is first drilled at a feeding speed and a rotational speed of a drill (1) which are selected. When the drilling of the workpiece is initiated, the amounts of the feed speed and the rotational speed are detected by a feed speed sensor (5) and a rotational speed sensor (6), respectively, and thrust force applied to the drill during the drilling is also detected by a thrust sensor (8). The detected feed speed and the rotational speed of the drill (1) are compared in a comparison unit (7) with optimum values which are adapted to the detected thrust force. When the detected values of the feed speed and the rotational speed of the drill coincide substantially with the optimum values, the drilling operation is performed, while when the detected values of the speed do not coincide with the optimum values, the feed speed and rotational speed of the drill are changed to the optimum values.

Description: The present invention relates to a drill control method and apparatus, and, more particularly, to a method and apparatus for controlling drilling operation when holes are drilled through a composite workpiece which is made of a plurality of materials of different machining properties. Ordinarily, holes are drilled by rotating and feeding a drill at a constant speed. However, in the case where holes are drilled through a composite workpiece made of a plurality of laminated materials of different machining properties, a drilling condition suitable for one of the materials may not be suitable for another material, and boundary-layer peeling or chipping phenomena tend to occur thereby resulting in deterioration of the quality of the drilled holes. In addition, the usable life of the drill tends to be short, and selection of the drilling condition is extremely difficult. In order to eliminate the difficulties described above, there has been developed a drilling control method wherein drilling conditions, such as the feed speed and the rotational speed are set beforehand, which are suitable for each material; each material is drilled constantly under the set conditions; the terminating point of drilling of the material is detected from the time required or from an amount of the feed of the drill; the drilling condition is then changed to another one suitable for the material of the next layer; and the drilling operation is carried out continuously by changing the drilling conditions one after the other as described above. For controlling the rotational speed of the drill, there has been proposed a method for controlling the spindle speed for the drill (for instance, refer to Japanese Patent Laid-Open (KOKAI) No. 274843/1986). In this method, a variable speed motor is used for driving the spindle, and this motor is controlled based on a difference between a command speed and an actual speed. For monitoring the cutting conditions, there has been proposed a device for controlling the machining condition (Japanese Patent Laid-Open (KOKAI) No. 15060/1987). In this device, a load cell is interposed between a chuck and a mounting surface therefor. The load cell detects the thrust force applied to the drill and delivers a voltage corresponding to the thrust. When the voltage exceeds a predetermined value, a terminating point of the drilling operation is detected without requiring any other positioning means. However, even if the drill feeding speed is controlled according to the method disclosed in Japanese Patent Laid-Open (KOKAI) No. 274843/1986, and the completion of the drilling of one material is determined by the device disclosed in Patent Laid-Open (KOKAI) No. 15060/1987, the process becomes too complicated because multiple drilling conditions equal to that of the number of materials must be set beforehand, and furthermore the feed speed and the rotational speed of the drill must be varied in accordance with the thickness of each material. In addition, the drilling condition even for the same material must be varied according to the thrust force applied to the drill for preventing the boundary layer from peeling and for improving the quality of the drill hole, and optimum control of the drill is difficult under such conditions. The known method does not provide such operations. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for controlling drilling operation, wherein the difficulties of the conventional method are eliminated without using complicated process. Another object of the invention is to provide a method and an apparatus for controlling the drilling operation wherein the setting of drilling conditions for a workpiece made of composite materials is not required, and each material of the workpiece is drilled depending on the thrust force detected through the operation of drilling the material. These and other objects of the present invention are achieved by the method of controlling the drilling operation for a workpiece as defined in claim 1. According to the present invention, there is also provided an apparatus for controlling the drilling operation of a workpiece as defined in claim 2. A preferred embodiment of the present invention will become understood from the following detailed description referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an apparatus for controlling drilling operations, according to the present invention; and FIG. 2 is a flow chart showing the steps of a method for controlling drilling operations, according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the block diagram of FIG. 1 showing general arrangement of the apparatus for controlling drilling operations of the present invention, a drill 1 is fixedly mounted on a drilling unit 2. The drill 1 is rotated by the drilling unit 2 and is shiftable toward and away from a workpiece 3, which is a composite workpiece made of a plurality of materials 3a and 3b having different machining properties. A control device 4 is connected to the drill unit 2 for controlling the rotational speed and the feed speed of the drill 1. The control device 4 comprises a rotational speed controller 4a and a feed speed controller 4b. A feed speed sensor 5 and a rotational speed sensor 6 are connected to the drill unit 2 for detecting the feed speed and the rotational speed of the drill 1, respectively. Furthermore, a thrust sensor 8 such as a load cell is coupled to the drill unit 2 for detecting axial thrust force applied to the drill 1 when the drill 1 is forced into the workpiece 3. Outputs of the feed speed sensor 5, the rotational speed sensor 6 and the thrust sensor 8 are supplied to a CPU 7 via data converters 9a, 9b, and 9c, such as A-D converters, respectively. In the CPU 7 there is stored or placed in beforehand optimum relationships of the values for the thrust force, the feed speed and the rotational speed of the drill 1 for respective materials of the workpiece. The CPU 7 functions to compare the output data obtained from the sensors 5,6 and 8 with the optimum relationships for the thrust force, the feed speed, and the rotational speed of the drill 1, and delivers an output to a correction circuit 10. The correction circuit 10 corrects the feed speed and the rotational speed depending on the output of the CPU 7, and delivers control signals to the rotational speed controller 4a and the feed speed control 4b of the control device 4. The control device 4 controls the rotational speed and the feed speed of the drill 1 depending on the control signals. FIG. 2 is a flow chart illustrating the method for controlling the drilling operation according to the present invention. At the start of the control, the thrust force applied to the drill 1 is set at zero before drilling. In step 1, the rotational speed and the feed speed are set for the first material of the workpiece. In step 2, the thrust force applied to the drill 1 due to the drilling of the first material is detected by the thrust sensor 8. In step 4, the rotational speed and the feed speed (condition (A)) of the drill 1 detected by the sensors 6 and 5 are compared with optimum rotational speed and optimum feed speed (optimum condition (B)) of the drill 1, which are determined depending on the detected thrust force in step 3. When it is determined in a step 4 that the condition (A) is at least substantially equal to the optimum condition (B), the drilling operation is carried out in a step 6 with the initially set speeds being maintained. However, at the step 4 when it is determined that the condition (A) is not substantially equal to the condition (B), the rotational speed and the feed speed are corrected in step 5 toward the optimum condition (B), and the process returns to the step 2 where the thrust force is detected. Then, the cycle (steps 2→3→4→5→2) repeats until the condition (A) becomes close to the condition (B). After that, whether or not an adaptive control is obtained is checked at a step 7 , and when the result is YES, the drilling operation for the material is terminated at step 8, whereas the process returns to the step 2 when the result is NO at the step 4. Thereafter, the drilling operation is carried out in the same manner for the second material of the workpiece. Although in the method described above, the rotational speed and feed speed are set at step 1, it will be apparent that the rotational speed and the feed speed set for the previously drilled material may be used for these values. Further, although the CPU 7 is used for memorizing the optimum conditions and comparing the outputs of the sensors 5, 6 and 8 with the optimum conditions, it will be understood that any other circuit adapted for accomplishing these functions may also be used instead of the CPU 7. According to the present invention, the optimum drilling operation is performed in the simple method in which the best feed speed and rotational speed for respective materials are taken by detecting the thrust force generated by the drilling operation. Therefore, accuracy and quality of the drilled holes are improved and usable life of the drill is increased. As it is not required to previously set the drilling condition according to thickness of the materials, the operation is facilitated and is made more rapid.

Claims: A method of controlling the drilling operation for a workpiece, wherein the rotational speed and the feed speed of the drill (1) and the thrust force applied to the drill are detected, and the drilling operation is controlled in relation to the detected rotational speed, feed speed and thrust force so as to maintain an optimum drilling condition for the workpiece, characterized by the steps of: providing the workpiece as a composite material (3) made of a plurality of laminated materials (3a, 3b); measuring an actual thrust force during the drilling operation for the workpiece; determining an optimum rotational speed and an optimum feed speed of the drill depending on the detected actual thrust force, the optimum rotational speed and the optimum feed speed being preliminarily set in the optimum relationships with the thrust force for each material of the workpiece; and controlling the rotational speed and the feed speed of the drill so as to converge to the optimum rotational speed and the optimum feed speed, respectively, thereby automatically setting best rotational speed and feed speed whenever the thrust force changes with respect to the change of materials to be drilled. An apparatus for controlling the drilling operation for a workpiece in response to a rotational speed sensor (6) for detecting the rotational speed of a drill (1), a feed speed sensor (5) for detecting the feed speed of the drill (1), a thrust force sensor (8) for detecting the thrust force applied to the drill (1), characterized in that the apparatus is for drilling a composite material (3) made of a plurality of laminated materials (3a, 3b); and that the apparatus comprises: determining means (9c, 7) for determining an optimum rotational speed and an optimum feed speed of the drill (1) depending on an actual thrust force detected by the thrust force sensors (8) during the drilling operation for the workpiece, the optimum rotational speed and said optimum feed speed being preliminarily set in the optimum relationships with the thrust force for each material of the workpiece; and controlling means for (10, 4) controlling the rotational speed and the feed speed of the drill so as to converge to the optimum rotational speed and the optimum feed speed, respectively, thereby automatically setting best rotational speed and feed speed whenever the thrust force changes with respect to the change of materials in the workpiece to be drilled.

Inventors: AIHARA YUKITAKA, AIHARA, YUKITAKA
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: G05B19
IPC codes: B23Q15, G05B19, B23B47