Front control system, area setting method and control panel for construction machine

Abstract: A setting device (7) comprises a direct setting switch (7a) for instructing the direct teaching setting, a numeral input key (7b) consisted of up- and down-keys (7b1, 7b2) for instructing the numeral input setting, a setting changeover switch (7c1) for changing over a setting mode from the direct teaching setting to the numeral input setting, an LED (7c2) lighting up when the setting changeover switch (7c1) is pushed, an area limiting switch (7d1) for staring the area limiting excavation control, an LED (7d2) lighting up when the area limiting switch (7d1) is pushed, and a display screen (7e) comprised of liquid crystals, etc. for indicating the position of a bucket end of a front device (1A) in terms of a numeral value when the setting changeover switch (7c1) is not pushed, and indicating the numeral value input with the numeral input setting when the setting changeover switch (7c1) is pushed. In a front control system for a construction machine, therefore, the operator can always select optimum area setting means in any of work sites and take appropriate and prompt actions for various types of works.

Description: The invention relates to a construction the features of the preamble of claim 1 and to a control machine having panel of such construction machine, which is disclosed in the US-A-5 308 219. There is known a hydraulic excavator as typical one of construction machines. In a hydraulic excavator, front members, such as a boom and an arm, making up a front device are operated by an operator manipulating respective manual control levers. However, because the front members are coupled to each other through articulations for relative rotation, it is very difficult to carry out excavation work within a predetermined area or in a predetermined plane by operating the front members. Also, when excavation work is performed in urban districts and so forth, due care must be paid to keep the front device from interfering with surrounding objects, e.g., electric wires and walls. In view of the above-mentioned state of art, various proposals for facilitating excavation work or preventing interference between the front device and surrounding objects have been made. For example, according to JP-A- 4-136324, a slowdown area is set in a position before reaching an entrance forbidden area, and a front device is slowed down by reducing an operation signal input from a control lever when a part, e.g., a bucket, of the front device enters the slowdown area, and is stopped when the bucket reaches the boundary of the entrance forbidden area. Also, this related art employs, as an area setting method, one mode in which the operator moves a bucket end onto the target boundary and pushes a switch there (direct teaching setting mode), or the other mode in which the operator inputs necessary numeral values through numeral input keys (numeral input setting mode). Further, according to WO 95/30059, an area to be excavated is set beforehand, and a part, e.g., a bucket, of a front device is controlled to slow down its movement only in the direction toward the excavation area when the bucket comes close to the boundary of the excavation area, and to be able to move along the boundary of the excavation area without going out of the excavation area when the bucket reaches the boundary of the excavation area. Also, this related art discloses an area setting method in which the operator moves a bucket end onto the target boundary and pushes a switch there (direct teaching setting mode). Meanwhile, when the operator sets an area where the front device is forbidden from entering, which one of setting modes is more convenient depends on the type of scheduled work. For example, when the ground should be generally leveled by rough excavation in the work site where an area to be excavated is not especially defined by numerals put on the drawing or the like, it is convenient for the operator to move a bucket end directly to a limit position of the excavation and perform setting operation, e.g., push a button or the like, thereby setting the area based on coordinate values of the bucket end (direct teaching setting). In some work sites, however, the depth by which the ground is to be excavated from the level of a hydraulic excavator on the ground surface is specified in unit of meter. In such a case, it is convenient to set an excavation area by an actual numeral value beforehand (numeral input setting). Furthermore, work of gradually proceeding excavation from the ground surface and digging up a pipe (water service pipe or the like) buried in earth requires the excavation to be first roughly made to some extent without any control and then finely made under area limiting excavation control from a certain depth. In this case, it is convenient to excavate the ground roughly to some extent without any control, then set the position reached at that time by the direct teaching, and then proceed the excavation gradually in steps of several centimeters in such a manner as like carefully peeling off a thin skin while setting the depth in a gradually increasing value with the above set position as a base, thus digging up the target pipe. However, the above related-art systems include only one area setting means, i.e., means for the direct teaching setting or means for the numeral input setting. This has raised a problem that the operator can neither always select optimum area setting means in any of work sites nor take appropriate and prompt actions for various types of works. In addition, during the operation under front control with the area setting described above, it is often desired to cancel the control for a while. For example, work of burring a water service pipe or the like in the ground is carried out with a hydraulic excavator by excavating a predetermined length of trench in a certain depth, then lifting the pipe and installing it in the trench at a predetermined position, and then excavating another length of trench. In other words, trench digging and pipe burring are repeated alternately. When the trench digging in such work is performed under area limiting excavation control, for example, the work is proceeded in a sequence of excavating a predetermined length of trench, turning off a control start switch on a control panel to bring the area limiting excavation control to an end once, lifting the pipe with a crane for desired installation, turning on the control start switch, and setting the excavation area again to excavate another length of trench. This results in complicated operation and makes the operator feel impatient therewith. In the US-A-5 308 219 - cited above - it is disclosed a construction machine comprising a front control system and a multi-articulated front device made up of a plurality of front members rotatable in the vertical direction and driven by hydraulic actuators. A plurality of hydraulic control valves are driven in accordance with respective operation signals input from a plurality of operating means for controlling flow rates of a hydraulic fluid supplied to the hydraulic actuators. The front control system controls the front device to be moved in a preset area and comprises first area setting means having a direct setting switch for setting an area where the front device is allowed to move, by direct teaching in response to an instruction from the direct setting switch, second area setting means having a numeral input switch for setting an area where the front device is allowed to move, by inputting a numeral value through the numeral input switch, and setting selection means for selecting one of the first area setting means and the second area setting means. According to the invention, the front control system further comprises display means for displaying the numeral value input through the numeral input switch of the second area setting means. With this feature, since the operator can make the numeral input setting while looking at the numeral value displayed on the display means, the numeral input setting can be precisely and promptly performed. The front control system further comprises display changeover means for instructing the display means to display a current position of the front device when the setting changeover switch is not operated, and instructing the display means to display the numeral value input through the numeral input switch of the second area setting means when the setting changeover switch is operated. With this feature, during the front control and the direct teaching setting, the current position of the front device is displayed on the display means, and the operator can perform work while confirming the current position of the front device on the display means. During the numeral input setting, the numeral value input through the numeral input switch is displayed on the display means, and the operator can proceed the setting while looking at the numeral value displayed on the display means. Preferably, the setting selection means has a setting changeover switch for enabling one of the first area setting means and the second area setting means to be selected when the setting changeover switch is not operated, and enabling the other of the first area setting means and the second area setting means to be selected when the setting changeover switch is operated. With this feature, by operating one switch of the first area setting means and the second area setting means, the setting can be performed by the one area setting means even with the setting changeover switch not operated. By operating the setting changeover switch, a setting mode is changed over to the setting by the other area setting means. Therefore, the setting changeover can be rationally achieved with a minimum switching operation. Preferably, the setting selection means enables the first area setting means to be selected regardless of whether the setting changeover switch is operated or not, when the direct setting switch of the first area setting means is operated, and enables the second area setting means to be selected when the setting changeover switch is operated. With this feature, by operating the direct setting switch of the first area setting means, the direct teaching setting can be made with no need of operating the setting changeover switch. Thus, the area setting can be performed with priority given to the direct teaching setting. Preferably, the numeral input switch of the second area setting means comprises a first numeral input key for increasing an input numeral value from a certain base value, and a second numeral input key for reducing an input numeral value from a certain base value. With this feature, the operator can freely make the numeral input setting by using the two keys. Preferably, the second area setting means previously sets, as an initial value, a value representing a position to which the front device cannot reach, and changes a set numeral value through the numeral input switch with the initial value as a base, thereby setting the area. With this feature, when the numeral input setting is made by the second area setting means, the area can be set to a desired position by using, as a base, the value representing a position to which the front device cannot reach. Preferably, the second area setting means changes a set numeral value through the numeral input switch with the numeral value set by the direct teaching as a base, thereby setting the area. With this feature, in such work as gradually proceeding excavation from the ground surface and digging up a pipe buried in earth is performed by first roughly excavating the earth some extent without any control, and then setting a greater depth step by step from a certain depth by inputting numeral values with the position set by the direct teaching as a base, so that the excavation is gradually proceeded in steps of several centimeters in such a manner as like carefully peeling off a thin skin. It is thus possible to quickly dig up the target pipe without damaging it. Preferably, the construction machine further comprises a control selection switch for selecting whether the front device is to be controlled or not, and initializing means for setting, as an initial value of the area to be set, a value representing a position to which the front device cannot reach, each time when the control selection switch is operated for selection of front control. With this feature, when the front control is selected, the position to which the front device cannot reach is always set initially. This enables the front device to freely move over a full range where it is inherently operable, for free setting of the excavation area within that full operable range. The construction machine further comprises control means for controlling operation of the front device by modifying the operation signal so that the front device is allowed to move within an area set by one of the first area setting means and the second area setting means, a temporary cancel switch, and control cancel means for temporarily cancelling control of the front device performed by the control means when the temporary cancel switch is pushed. By providing the temporary cancel switch so that the front control executed by the control means can be temporarily cancelled, an excavation mode can be easily changed over between excavation under the normal control and excavation under the area limiting control. It is thus possible to quickly and smoothly perform digging work requiring a combination of the normal excavation and the excavation under the area limiting control, such as work of burying a water service pipe or the like in the ground by alternately repeating trench digging for which the excavation under the area limiting control is more convenient and pipe installation for which the normal excavation is more convenient. Preferably, the temporary cancel switch is provided on a lever grip of one of the plurality of control lever means. By providing the temporary cancel switch on the lever grip of the control lever, the operator can promptly change over the normal excavation and the excavation under the area limiting control from one to the other without releasing his hand from the control lever. Preferably, the direct setting switch and the numeral input switch are provided on a box-type control panel installed in a cab, and the temporary cancel switch is provided on a lever grip of one of the plurality of control lever means. With this feature, the operator can set an area to be excavated by using the direct setting switch or the numeral input switch on the control panel prior to the start of work, and during the work, can promptly change over the normal excavation and the excavation under the area limiting control from one to the other without releasing his hand from the control lever, by using the temporary cancel switch provided on the lever grip of the control lever means. Preferably, the first area setting means further includes another direct setting switch provided on the lever grip for instructing setting of the area where the front device is allowed to move. By providing not only the temporary cancel switch but also another direct setting switch on the lever grip of the control lever means, the operator can also promptly set the excavation area without releasing his hand from the control lever. This makes the operator not feel troublesome in setting the excavation area. Preferably, the temporary cancel switch and the direct setting switch both provided on the lever grip have surface configurations different from each other. With this feature, while the direct setting switch and the temporary cancel switch are both installed on the same control lever, the operator can discern the respective functions of the two switches just by touching them without visually confirming the switches, resulting in quicker and smoother operation. Preferably, the control lever means on which the temporary cancel switch is provided is the control lever means for a boom of a hydraulic excavator. By providing the direct setting switch on the control lever of the boom control lever means which instructs the vertical movement of the front device, the operator can push the temporary cancel switch to change over the excavation mode between the normal excavation and the excavation under the area limiting control while manipulating the control lever to move the boom with the same hand. Also, when the direct setting switch is provided on the control lever of the above control lever means, the operator can set the area with his one hand while manipulating the control lever to move the boom with the same hand. As a result, the height can be easily adjusted in setting the area and the delicate setting is facilitated. Preferably, the control cancel means is means for interrupting modification of the operation signal made by the control means when the temporary cancel switch is pushed. By interrupting modification of the operation signal, the control of the front device is temporarily suspended. Preferably, the control cancel means is means for temporarily changing the set position of a boundary of the area to a value representing a position to which the front device cannot reach, when the temporary cancel switch is pushed. By temporarily changing the set position of the boundary of the area, the control of the front device is made essentially infeasible and cancelled for a while. Further, to achieve the above first object, the present invention provides an area setting method for use in front control under which a multi-articulated front device made up of a plurality of front members rotatable in the vertical direction is controlled so that the front device is moved in a preset area, comprising the steps of moving the front device to a position as a reference, storing the position by direct teaching, setting a depth by inputting a numeral value with the stored position as a base, and setting an area where the front device is allowed to move, in accordance with a numeral value resulted from the depth setting. With this feature, in such work as gradually proceeding excavation from the ground surface and digging up a pipe buried in earth, it is possible to quickly dig up the target pipe. Furthermore, the present invention provides a control panel for a construction machine comprising a multi-articulated front device made up of a plurality of front members rotatable in the vertical direction, a plurality of hydraulic actuators for driving respectively the plurality of front members, and a plurality of hydraulic control valves driven in accordance with respective operation signals input from a plurality of operating means for controlling flow rates of a hydraulic fluid supplied to the plurality of hydraulic actuators, the front control system controlling the front device to be moved in a preset area, wherein the control panel comprises a direct setting switch for instructing by direct teaching setting of an area where the front device is allowed to move, a numeral input switch for instructing by input of a numeral value setting of an area where the front device is allowed to move, and setting changeover switch for selecting one of the setting instructions from the direct setting switch and the numeral input switch. The control panel further comprises display means for displaying the numeral value input through the numeral input switch, so that the operator can precisely make the numeral input setting while looking at the numeral value displayed on the display means. The control panel further comprises display means for displaying a current position of the front device when the setting changeover switch is not operated, and displaying the numeral value input through the numeral input switch when the setting changeover switch is operated, so that the operator can obtain information about the position of the front device as well from the display means. Preferably, the numeral input switch comprises a first numeral input key for increasing an input numeral value from a certain base value, and a second numeral input key for reducing an input numeral value from a certain base value. Preferably, the control panel further comprises a control selection switch for selecting whether the front device is to be controlled or not, whereby selection of the control of the front device by the control selection switch enables the direct setting switch and the numeral input switch to instruct the setting. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a front control system for a construction machine according to a first embodiment of the present invention, along with a hydraulic drive system thereof. Fig. 2 is a view showing an appearance of a hydraulic excavator to which the present invention is applied. Fig. 3 is an illustrative view showing an appearance of a setting device. Fig. 4 is a functional block diagram showing control functions of a control unit. Fig. 5 is a side view for explaining a manner of setting an excavation area for use in area limiting excavation control according to the first embodiment. Fig. 6 is a flowchart showing processing steps executed in an area setting calculation portion. Fig. 7 is a graph showing the relationship between a distance to a bucket end from a boundary of the set area and a bucket end speed limit value, the relationship being used when the limit value is determined. Fig. 8 is an illustrative view showing differences in operation of modifying a boom-dependent bucket end speed among the case of a bucket end positioned inside the set area, the case of the bucket end positioned on the set area, and the case of the bucket end positioned outside the set area. Fig. 9 is an illustrative view showing one example of a locus along which the bucket end is moved under modified operation when it is inside the set area. Fig. 10 is an illustrative view showing one example of a locus along which the bucket end is moved under modified operation when it is outside the set area. Fig. 11 is a diagram showing a front control system for a construction machine according to a second embodiment of the present invention, along with a hydraulic drive system thereof. Fig. 12 is a block diagram showing control functions of a control unit. Fig. 13 is a block diagram showing control functions of the control unit for explaining, as a third embodiment, a modification of the second embodiment of the present invention. Fig. 14 is a flowchart showing processing steps executed in an area setting calculation portion, for explaining another modified (fourth) embodiment of the present invention. Fig. 15 is a flowchart showing processing steps executed in an area setting calculation portion, for explaining still another modified embodiment of the present invention. Fig. 16 is an illustrative view showing, as a sixth embodiment, another example of the setting device in the front control system of the present invention. Fig. 17 is a diagram showing a front control system for a construction machine according to a still another (seventh) embodiment of the present invention, along with a hydraulic drive system thereof. Fig. 18 is a perspective view showing an appearance of a grip portion of a control lever in which a direct setting switch and a temporary cancel switch are provided. Fig. 19 is a functional block diagram showing control functions of a control unit. Fig. 20 is a flowchart showing processing steps executed in an area limiting control changeover calculating portion. Fig. 21 is a block diagram showing control functions of the control unit for explaining, as an eighth embodiment, a modification of the seventh embodiment of the present invention. Fig. 22 is a flowchart showing processing steps executed in an area setting calculation portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Several embodiments of the present invention in which the invention is applied to an area limiting excavation control system for a hydraulic excavator will be described hereunder with reference to the drawings. To begin with, a first embodiment of the present invention will be described with reference to Figs. 1 to 10. In Fig. 1, a hydraulic excavator to which the present invention is applied comprises a hydraulic pump 2, a plurality of hydraulic actuators driven by a hydraulic fluid from the hydraulic pump 2, including a boom cylinder 3a, an arm cylinder 3b, a bucket cylinder 3c, a swing motor 3d and left and right track motors 3e, 3f, a plurality of control lever units 4a - 4f provided respectively associated with the hydraulic actuators 3a-3f, a plurality of flow control valves 5a - 5f connected between the hydraulic pump 2 and the plurality of hydraulic actuators 3a - 3f and controlled in accordance with respective operation signals input from the control lever units 4a - 4f for controlling respective flow rates of the hydraulic fluid supplied to the hydraulic actuators 3a - 3f, and a relief valve 6 which is opened when the pressure between the hydraulic pump 2 and the flow control valves 5a - 5f exceeds a preset value. The above components cooperatively make up a hydraulic drive system for driving driven members of the hydraulic excavator. As shown in Fig. 2, the hydraulic excavator is made up of a multi-articulated front device 1A comprising a boom 1a, an arm 1b and a bucket 1c which are each rotatable in the vertical direction, and a body 1B comprising an upper structure 1d and an undercarriage 1e. The boom 1a of the front device 1A is supported at its base end to a front portion of the upper structure 1d. The boom 1a, the arm 1b, the bucket 1c, the upper structure 1d and the undercarriage 1e serve as driven members which are driven respectively by the boom cylinder 3a, the arm cylinder 3b, the bucket cylinder 3c, the swing motor 3d and the left and right track motors 3e, 3f. These driven members are operated in accordance with instructions from the control lever units 4a - 4f. Further, the control lever units 4a - 4f are of hydraulic pilot type each generating a pilot pressure depending on the input amount and the direction by and in which the control levers 40a - 40f are each manipulated by the operator, and supplying the pilot pressure to corresponding one of hydraulic driving sectors 50a - 55b of the flow control valves 5a - 5f through pilot lines 44a - 49b, thereby driving these flow control valves. An area limiting excavation control system of this embodiment is equipped on the hydraulic excavator constructed as explained above. The control system comprises a setting device 7 for providing an instruction to set an excavation area where a predetermined part of the front device, e.g., an end of the bucket 1c, is allowed to move for excavation, depending on the scheduled work beforehand, angle sensors 8a, 8b, 8c disposed respectively at pivot points of the boom 1a, the arm 1b and the bucket 1c for detecting respective rotational angles thereof as status variables in relation to the position and posture of the front device 1A, a tilt angle sensor 8d for detecting a tilt angle of the body 1B in the back-and-forth direction, pressure sensors 61a, 61b disposed in the pilot lines 45a, 45b of the arm control lever unit 4b for detecting respective pilot pressures representative of the input amount by which the control lever unit 4b is operated, a proportional solenoid valve 10a connected at its primary port side to a pilot pump 43 for reducing a pilot pressure from the pilot pump 43 in accordance with an electric signal applied thereto and outputting the reduced pilot pressure, a shuttle valve 12 connected to the pilot line 44a of the boom control lever unit 4a and the secondary port side of the proportional solenoid valve 10a for selecting higher one of the pilot pressure in the pilot line 44a and the control pressure delivered from the proportional solenoid valve 10a and introducing the selected pressure to the hydraulic driving sector 50a of the flow control valve 5a, a proportional solenoid valve 10b disposed in the pilot line 44b of the boom control lever unit 4a for reducing the pilot pressure in the pilot line 44b in accordance with an electric signal applied thereto and outputting the reduced pilot pressure, and a control unit 9 for receiving a setup signal from the setting device 7 and detection signals from the angle sensors 8a, 8b, 8c, the tilt angle sensor 8d and the pressure sensors 61a, 61b, setting the excavation area where the end of the bucket 1c is allowed to move, and outputting to the proportional solenoid valves 10a, 10b electric signals for modifying the operation signals to carry out control for excavation within a limited area. The setting device 7 outputs a setup signal to the control unit 9 to instruct setting of the excavation area. As shown in Fig. 3, the setting device 7 comprises a direct setting switch 7a for instructing the direct teaching setting, a numeral input key 7b consisted of an up-key 7b1 and a down-key 7b2 for instructing the numeral input setting, a setting changeover switch 7c1 pushed when a setting mode is to be changed from the direct teaching setting to the numeral input setting, an LED 7c2 lighting up when the setting changeover switch 7c1 is pushed, an area limiting switch 7d1 pushed when the area limiting excavation control is to be performed, an LED 7d2 lighting up when the area limiting switch 7d1 is pushed, and a display screen 7e comprised of liquid crystals, etc. for indicating the position of the bucket end of the front device 1A in terms of a numeral value when the setting changeover switch 7c1 is not pushed, and indicating the numeral value input with the numeral input setting when the setting changeover switch 7c1 is pushed. Further, the setting device 7 is constructed of a box-type control panel, for example, and installed in a position above a standard control panel, which is usually installed in a cab forwardly of an operator's seat, and out of interference with a visual field of the operator, e.g., in a front corner of the cab. Fig. 4 shows control functions of the control unit 9. The control unit 9 has various functions executed by a front posture calculating portion 9a, an area setting calculating portion 9b, a bucket end speed limit value calculating portion 9c, an arm cylinder speed calculating portion 9d, an arm-dependent bucket end speed calculating portion 9e, a boom-dependent bucket end speed limit value calculating portion 9f, a boom cylinder speed limit value calculating portion 9g, a boom pilot pressure (boom command) limit value calculating portion 9h, an area limiting control changeover calculating portion 9r, a boom command calculating portion 9i, and a display changeover control calculating portion 9s. The front posture calculating portion 9a calculates the position and posture of the front device 1A based on the respective rotational angles of the boom, the arm and the bucket detected by the angle sensors 8a - 8c, as well as the tilt angle of the body 1B in the back-and-forth direction detected by the tilt angle sensor 8d. One example of the calculation process will be described with reference to Fig. 5. Note that the following example is to calculate the position of a bucket prong end P 1 of the front device 1A excepting the tilt angle detected by the tilt angle sensor 8d for the sake of brevity. Referring to Fig. 5, the control unit 9 stores various dimensions of the front device 1A and the body 1B in its memory, and the front posture calculating porion 9a calculates the position of the bucket end P 1 based on the stored data and the values of rotational angles α, β, γ detected respectively by the angle sensors 8a, 8b, 8c. At this time, the position of P 1 is determined as coordinate values (X, Y) on an XY-coordinate system with the crigin defined by, for example, the pivot point of the boom 1a. The XY-coordinate system is a rectangular coordinate system fixed on the body 1B and lying in a vertical plane. Given that the distance between the pivot point of the boom 1a and the pivot point of the arm 1b is L 1 , the distance between the pivot point of the arm 1b and the pivot point of the bucket 1c is L 2 , and the distance between the pivot point of the bucket 1c and the end of the bucket 1c is L 3 , the coordinate values (X, Y) on the XY-coordinate system are determined from the rotational angles α, β, γ by using formulae below: X = L 1 sinα + L 2 sin(α + β) + L 3 sin(α + β + γ) Y = L 1 cosα + L 2 cos(α + β) + L 3 cos(α + β + γ) The area setting calculating portion 9b executes setting of an excavation area where the end of the bucket 1c is allowed to move for excavation, in response to an instruction from the setting device 7 by the direct teaching setting with the direct setting switch 7a or the numeral input setting with the numeral input switch 7b. One example of the setting process will be described with reference to Figs. 5 and 6. In this example, a boundary L of the excavation area is set as a straight line parallel to the X-axis at a depth h 1 . Referring to Fig. 6, the area limiting excavation control in this embodiment is started by turning on (pushing) the area limiting switch 7d1 (step 100). The turning-on of the area limiting switch 7d1 lights up the LED 7d2 (step 110). Then, a value representing a so deep position that the bucket cannot reach there is set as an initial value of the boundary L (depth h 1 ) of the excavation area (step 120). This enables the front device 1A to freely move over a full range where it is inherently operable, for free setting of the excavation area within that full operable range. Here, the initial value of the boundary L of the excavation area is set to, as one example, Y = - 20 m. Next, the boundary L of the excavation area is set as follows by operating the direct setting switch 7a, the numeral input switch 7b and the setting changeover switch 7c1 in a combined manner. (a) Direct Teaching Setting After moving the end P 1 of the bucket 1c to a target position, the operator pushes the direct setting switch 7a. Upon the direct setting switch 7a being pushed, the area setting calculating portion 9b always sets the boundary L of the excavation area below by using the Y-coordinate value, Y = Y 1 , Y 2 , Y 4 , of the bucket end P 1 calculated in the front posture calculating portion 9a at that time; set value = Y-coordinate value Y 1 (step 140) set value = Y-coordinate value Y 2 (step 160) set value = Y-coordinate value Y 4 (step 220) (these setting processes follow respective paths; (L) steps 130 → 140 → 150 → 240 → 130 → 240; (2) steps 130 → 140 → 150 → 160 → 240 → 130 → 240; and paths; (3) steps 130 → 190 → 200 or 210 → 220 → 240 → 130 → 240. (b) Numeral Input Setting When the setting changeover switch 7c1 is pushed to select the numeral input setting and the direct teaching setting will never be performed after that, the area setting calculating portion 9b sets the boundary L of the excavation area upon operation of the up-key 7b1 or the down-key 7b2 of the numeral input switch 7b below by using the initial value Y = - 20 m as a base (reference) and adding a change dY 3 , dY 4 input from the up- or down-key 7b1, 7b2 to the initial value; set value = - 20 + dY 3 (step 200) set value = - 20 + dY 4 (step 230) (these setting processes follow respective paths; (1) steps 130 → 190 → 200 → 210 → 240 → 130 → 240; and (2) steps 130 → 190 → 200 or 210 → 230 → 240 → 130 → 240. (c) Direct Teaching Setting → Numeral Input Setting When the setting changeover switch 7c1 is pushed to select the numeral input setting and the up-key 7b1 or the down-key 7b2 of the numeral input switch 7b is operated after the direct teaching setting has been once performed, the area setting calculating portion 9b sets the boundary L of the excavation area below by using the value Y 1 set by the direct teaching as a base and adding a change dY 2 input from the up- or down-key 7b1, 7b2 to that set value; set value = Y 1 + dY 2 (step 180) (this setting process follows a path of steps 130 → 140 → 150 → 170 → 180 → 240 → 130 → 240). Even with Y 1 + dY 2 thus once set, if the direct setting switch 7a is pushed as mentioned in the above (a), the direct teaching setting is preceded. Therefore, if the setting changeover switch 7c1 is pushed and a numeral value is input upon operation of the up- or down-key 7b1, 7b2 after that, the area setting calculating portion 9b sets the boundary L of the excavation area below by making calculation using a value Y 1 newly set by the direct teaching as a base; set value = Y 1 + dY 2 (step 180) (this setting process follows a path of steps 130 → 140 → 150 → 170 → 180 → 240 → 130 → 140 → 150 → 170 → 180 → 240 → 130 → 240). When the direct teaching setting is performed by positioning the bucket end on the ground surface and designating the level of the ground surface as a set value, as shown in Fig. 5, the change dY 2 input through the down-key 7b2 represents the depth h 1 . This means that the operator eventually inputs the depth h 1 in a numeral value. In the above (b) and (c), the change set upon operation of the up- or down-key 7b1, 7b2 is not particularly restricted in value to be input. However, setting to such a value as representing the position not reachable by the front device 1A is meaningless from the practical point of view. Accordingly, the change set upon operation of the up- or down-key 7b1, 7b2 is specified as a value within the range or area reachable by the front device 1A. It is here, by way of example, assumed that a value up to ± 20 m is allowed to input and any value beyond such a limit cannot be input. When the area limiting excavation control in this embodiment is to be ended, the area limiting switch 7d1 is turned off by pushing it again (step 240). For safety, the set value of the boundary L of the excavation area is reset to the initial value of Y = - 20 m (step 250). The LED 7d2 is turned out (step 260) and the control flow is then brought to an end (step 270). After setting the boundary L of the excavation area as described above, the area setting calculating portion 9b derives a formula of a straight line expressing the boundary L of the excavation area, establishes an XaYa-coordinate system which is a rectangular coordinate system having the origin located on that straight line and one axis defined by that straight line, and determines transform data from the XY-coordinate system to the XaYa-coordinate system. The bucket end speed limit value calculating portion 9c calculates a limit value a of the component of the bucket end speed vertical to the boundary L of the set area depending on a distance D to the bucket end from the boundary L. This calculation is carried out by storing the relationship as shown in Fig. 7 in the memory of the control unit 9 beforehand and reading out the stored relationship. In Fig. 7, the horizontal axis represents the distance D to the bucket end from the boundary L of the set area, and the vertical axis represents the limit value a of the component of the bucket end speed vertical to the boundary L. As with the XaYa-coordinate system, the distance D on the horizontal axis and the speed limit value a on the vertical axis are each defined to be positive (+) in the direction toward the inside of the set area from the outside of the set area. The relationship between the distance D and the limit value a is set such that when the bucket end is inside the set area, a speed in the negative (-) direction proportional to the distance D is given as the limit value a of the component of the bucket end speed vertical to the boundary L, and when the bucket end is outside the set area, a speed in the positive (+) direction proportional to the distance D is given as the limit value a of the component of the bucket end speed vertical to the boundary L. Accordingly, inside the set area, the bucket end is slowed down only when the component of the bucket end speed vertical to the boundary L exceeds the limit value in the negative (-) direction, and outside the set area, the bucket end is sped up in the positive (+) direction. The arm cylinder speed calculating portion 9d estimates an arm cylinder speed based on a command value (pilot pressure) applied to the flow control valve 5b for the arm, which is detected by the pressure sensor 61a, 61b, and the flow rate characteristic of the flow control valve 5b. The arm-dependent bucket end speed calculating portion 9e calculates an arm-dependent bucket end speed b based on the arm cylinder speed and the position and posture of the front device 1A determined in the front posture calculating portion 9a. The boom-dependent bucket end speed limit value calculating portion 9f transforms the arm-dependent bucket end speed b , which has been determined in the calculating portion 9e, from the XY-coordinate system to the XaYa-coordinate system by using the transform data determined in the area setting calculating portion 9b, calculates arm-dependent bucket end speeds (b x , b y ), and then calculates a limit value c of the component of the boom-dependent bucket end speed vertical to the boundary L based on the limit value a of the component of the bucket end speed vertical to the boundary L determined in the calculating portion 9c and the component b y of the arm-dependent bucket end speed vertical to the boundary L. Such a process will now be described with reference to Fig. 8. In Fig. 8, the difference (a - b y ) between the limit value a of the component of the bucket end speed vertical to the boundary L determined in the bucket end speed limit value calculating portion 9c and the component b y of the arm-dependent bucket end speed b vertical to the boundary L determined in the arm-dependent bucket end speed calculating portion 9e provides a limit value c of the boom-dependent bucket end speed vertical to the boundary L. Then, the boom-dependent bucket end speed limit value calculating portion 9f calculates the limit value c from the formula of c = a - b y . The meaning of the limit value c will be described separately for the case where the bucket end is inside the set area, the case where the bucket end is on the boundary of the set area, and the case where the bucket end is outside the set area. When the bucket end is inside the set area, the bucket end speed is restricted to the limit value a of the component of the bucket end speed vertical to the boundary L in proportion to the distance D to the bucket end from the boundary L and, therefore, the component of the boom-dependent bucket end speed vertical to the boundary L is restricted to c (= a - b y ). Thus, if the component b y of the bucket end speed b vertical to the boundary L exceeds c , the boom is slowed down to c . When the bucket end is on the boundary L of the set area, the limit value a of the component of the bucket end speed vertical to the boundary L is set to 0, and the arm-dependent bucket end speed b toward the outside of the set area is cancelled out through the compensating operation of boom-up at the speed c . Thus, the component b y of the bucket end speed vertical to the boundary L becomes 0. When the bucket end is outside the set area, the component of the bucket end speed vertical to the boundary L is restricted to the upward speed a in proportion to the distance D to the bucket end from the boundary L. Thus, the compensating operation of boom-up at the speed c is always performed so that the bucket end is restored to the inside of the set area. The boom cylinder speed limit value calculating portion 9g calculates a limit value of the boom cylinder speed through the coordinate transformation using the aforesaid transform data based on the limit value c of the component of the boom-dependent bucket end speed vertical to the boundary L and the position and posture of the front device 1A. The boom pilot pressure limit value calculating portion 9h determines, based on the flow rate characteristic of the flow control valve 5a for the boom, a limit value of the boom pilot pressure (boom command) corresponding to the limit value of the boom cylinder speed determined in the calculating portion 9g. The area limiting control changeover calculating portion 9r outputs, as the limit value of the boom pilot pressure, the value calculated in the calculating portion 9h as it is when the area limiting switch 7d1 is turned on (pushed) and the area limiting excavation control is selected, and outputs, as the limit value of the boom pilot pressure, a maximum value when the area limiting switch 7d1 is turned off (not pushed) and the area limiting excavation control is not selected. The boom command calculating portion 9i receives the limit value of the pilot pressure from the calculating portion 9r and when the received limit value is positive, it outputs a voltage corresponding to the limit value to the proportional solenoid valve 10a on the boom-up side, thereby restricting the pilot pressure imposed on the hydraulic driving sector 50a of the flow control valve 5a to that limit value, and outputs a voltage of 0 to the proportional solenoid valve 10b on the boom-down side, thereby making zero (0) the pilot pressure imposed on the hydraulic driving sector 50b of the flow control valve 5a. When the received limit value is negative, the boon command calculating portion 9i outputs a voltage corresponding to the limit value to the proportional solenoid valve 10b on the boom-down side, thereby restricting the pilot pressure imposed on the hydraulic driving sector 50b of the flow control valve 5a to that limit value, and outputs a voltage of 0 to the proportional solenoid valve 10a on the boom-up side, thereby making nil (0) the pilot pressure imposed on the hydraulic driving sector 50a of the flow control valve 5a. The display changeover control calculating portion 9s indicates the position of the bucket end P 1 calculated in the front posture calculating portion 9a in numeral value when the setting changeover switch 7c1 is turned off (not pushed) and the numeral input setting is not selected, and indicates the position designated by the numeral input setting when the setting changeover switch 7c1 is turned on (pushed) and the numeral input setting is not selected. The operation of this embodiment having the above-explained arrangement will be described below in connection with the case where the area limiting switch 7d1 is turned on and the area limiting excavation control is performed. The following description will be made on several work examples; i,e., the case of operating the control lever of the boom control lever unit 4a in the boom-down direction to lower the boom with the intention of positioning the bucket end (i.e., the boom-down operation), and the case of operating the control lever of the arm control lever unit 4b in the arm-crowding direction to crowd the arm with the intention of digging the ground toward the body (i.e., the arm crowding operation). When the control lever of the boom control lever unit 4a is operated in the boom-down direction with the intention of positioning the bucket end, a pilot pressure representative of the command value from the control lever unit 4a is applied to the hydraulic driving sector 50b of the flow control valve 5a on the boom-down side through the pilot line 44b. At the same time, the bucket end speed limit value calculating portion 9c calculates, based on the relationship shown in Fig. 7, a limit value a (< 0) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area, the boom-dependent bucket end speed limit value calculating portion 9f calculates a limit value c = a (< 0) of the boom-dependent bucket end speed, and the boom pilot pressure limit value calculating portion 9h calculates a negative limit value of the boom pilot pressure corresponding to the limit value c . Then, the boon command calculating portion 9i outputs a voltage corresponding to the calculated limit value to the proportional solenoid valve 10b, thereby restricting the pilot pressure applied to the hydraulic driving sector 50b of the flow control valve 5a on the boom-down side, and also outputs a voltage of 0 to the proportional solenoid valve 10a for making nil (0) the pilot pressure applied to the hydraulic driving sector 50a of the flow control valve 5a on the boom-up side. Here, when the bucket end is far away from the boundary L of the set area, the limit value of the boom pilot pressure determined in the calculating portion 9h has an absolute value greater than that of the pilot pressure from the control lever unit 4a, and therefore the proportional solenoid valve 10b outputs the pilot pressure from the control lever unit 4a as it is. Accordingly, the boom is gradually moved down depending on the pilot pressure from the control lever unit 4a. As the boom is gradually moved down and the bucket end comes closer to the boundary L of the set area as mentioned above, the limit value c = a (< 0) of the boom-dependent bucket end speed calculated in the calculating portion 9f is increased (its absolute value |a| or |c| is reduced) and an absolute value of the corresponding boom command limit value (< 0) calculated in the calculating portion 9h is reduced. Then, when the absolute value of the limit value becomes smaller than the command value from the control lever unit 4a and the voltage output to the proportional solenoid valve 10b from the boom command calculating portion 9i is reduced correspondingly, the proportional solenoid valve 10b reduces and then outputs the pilot pressure from the control lever unit 4a for gradually restricting the pilot pressure applied to the hydraulic driving sector 50b of the flow control valve 5a on the boom-down side depending on the limit value c . Thus, the boom-down speed is gradually restricted as the bucket end comes closer to the boundary L of the set area, and the boom is stopped when the bucket end reaches the boundary L of the set area. As a result, the bucket end can be easily and smoothly positioned. When the bucket end has moved out beyond the boundary L of the set area, the limit value a (= c ) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area is calculated as a positive value in the calculating portion 9c based on the relationship shown in Fig. 7, and the boom command calculating portion 9i outputs a voltage corresponding to the limit value c to the proportional solenoid valve 10a for applying a pilot pressure corresponding to the limit value a to the hydraulic driving sector 50a of the flow control valve 5a on the boom-up side. The boom is thereby moved in the boom-up direction at a speed proportional to the distance D for restoration toward the inside of the set area, and then stopped when the bucket end is returned to the boundary L of the set area. As a result, the bucket end can be more smoothly positioned. Further, when the control lever of the arm control lever unit 4b is operated in the arm-crowding direction with the intention of digging the ground toward the body, a pilot pressure representative of the command value from the control lever unit 4b is applied to the hydraulic driving sector 51a of the flow control valve 5b on the arm-crowding side, causing the arm to be moved down toward the body. At the same time, the pilot pressure from the control lever unit 4b is detected by the pressure sensor 61a and input to the calculating portion 9d which calculates an arm cylinder speed. Then, the calculating portion 9e calculates an arm-dependent bucket end speed b . On the other hand, the calculating portion 9c calculates, based on the relationship shown in Fig. 7, a limit value a (< 0) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area, and the calculating portion 9f calculates a limit value c = a - b y of the boom-dependent bucket end speed. Here, when the bucket end is so far away from the boundary L of the set area as to meet the relationship of a < b y (|a| > |b y |), the limit value c is calculated as a negative value in the calculating portion 9f. Therefore, the boom command calculating portion 9i outputs a voltage corresponding to the calculated limit value to the proportional solenoid valve 10b, thereby restricting the pilot pressure applied to the hydraulic driving sector 50b of the flow control value 5a on the boom-down side, and also outputs a voltage of 0 to the proportional solenoid valve 10a for making nil (0) the pilot pressure applied to the hydraulic driving sector 50a of the flow control valve 5a on the boom-up side. At this time, since the control lever unit 4a is not operated, no pilot pressure is applied to the hydraulic driving sector 50b of the flow control valve 5a. As a result, the arm is gradually moved toward the body depending on the pilot pressure from the control lever unit 4b. As the arm is gradually moved toward the body and the bucket end comes closer to the boundary L of the set area as mentioned above, the limit value a of the bucket end speed calculated in the calculating portion 9c is increased (its absolute value |a| is reduced). Then, when the limit value a becomes greater than the component b y of the arm-dependent bucket end speed b vertical to the boundary L calculated in the calculating portion 9e, the limit value c = a - b y of the boom-dependent bucket end speed is calculated as a positive value in the calculating portion 9f. Therefore, the boom command calculating portion 9i outputs a voltage corresponding to the limit value c to the proportional solenoid valve 10a on the boom-up side, thereby restricting the pilot pressure applied to the hydraulic driving sector 50a of the flow control valve 5a to that limit value, and also outputs a voltage of 0 to the proportional solenoid valve 10b on the boom-down side for making nil (0) the pilot pressure applied to the hydraulic driving sector 50b of the flow control valve 5a. Accordingly, the boom-up operation for modifying the bucket end speed is performed such that the component of the bucket end speed vertical to the boundary L is gradually restricted in proportion to the distance D to the bucket end from the boundary L. Thus, direction change control is carried out with a resultant of the unmodified component b x of the arm-dependent bucket end speed parallel to the boundary L and the speed component vertical to the boundary L modified depending on the limit value c , as shown in Fig. 9, enabling the excavation to be performed along the boundary L of the set area. Further, when the bucket end has moved out beyond the boundary L of the set area, the limit value a of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area is calculated as a positive value in the calculating portion 9c based on the relationship shown in Fig. 7, the limit value c = a - b y (> 0) of the boom-dependent bucket end speed calculated in the calculating portion 9f is increased in proportion to the limit value a , and the voltage output from the boom command calculating portion 9i to the proportional solenoid valve 10a on the boom-up side is increased depending on the limit value c . In the case of the bucket end having moved out of the set area, therefore, the boom-up operation for modifying the bucket end speed is performed so that the bucket end is restored toward the inside of the set area at a speed proportional to the distance D. Thus, the excavation is carried out with a resultant of the unmodified component b x of the arm-dependent bucket end speed parallel to the boundary L and the speed component vertical to the boundary L modified depending on the limit value c , while the bucket end is gradually returned to and moved along the boundary L of the set area as shown in Fig. 10. Consequently, the excavation can be smoothly performed along the boundary L of the set area just by crowding the arm. With this embodiment, as described above, when the bucket end is inside the set area, the component of the bucket end speed vertical to the boundary L of the set area is restricted in accordance with the limit value a in proportion to the distance D to the bucket end from the boundary L of the set area. Therefore, in the boom-down operation, the bucket end can be easily and smoothly positioned, and in the arm crowding operation, the bucket end can be moved along the boundary L of the set area. This enables the excavation to be efficiently and smoothly performed within a limited area. When the bucket end is outside the set area, the front device is controlled to return to the set area in accordance with the limit value a in proportion to the distance D to the bucket end from the boundary L of the set area. Therefore, even when the front device is moved quickly, the front device can be moved along the boundary L of the set area and the excavation can be precisely performed within a limited area. Further, since the bucket end is slowed down under the direction change control before reaching the boundary of the set area as described above, an amount by which the bucket end projects out of the set area is reduced and a shock caused upon the bucket end returning to the set area is greatly alleviated. Therefore, even when the front device is moved quickly, the front device can be smoothly moved back to the set area and the excavation can be smoothly performed within a limited area. Additionally, since this embodiment includes, as means for setting the excavation area in the area limiting excavation control, both area setting means adapted for the direct teaching setting and the numeral input setting, the operator can select optimum area setting means in any of work sites, take prompt actions for various types of works, and implement excavation work in an appropriate and expeditious manner. For example, when the ground should be generally leveled by rough excavation in the work site where an area to be excavated is not especially defined by numerals put on the drawing or the like, the excavation area can be speedily set with the above function (a) of the direct teaching setting by placing the bucket end directly to a target position for excavation and pushing the direct setting switch 7a. In some work sites, however, the depth by which the ground is to be excavated from the level of a hydraulic excavator on the ground surface is specified in unit of meter. In such a case, by pushing the setting changeover switch 7c1 and inputting the specified depth through the numeral input switch 7b, a desired excavation area can be promptly set with the above function (b) of numeral input setting) and the excavation work can be performed under optimum control. Further, work of gradually proceeding excavation from the ground surface and digging up a pipe (water service pipe or the like) buried in earth is performed by first roughly excavating the earth some extent without any control, then setting the position reached at that time by the direct teaching, and then setting a greater depth step by step by inputting numeral values with that position as a base in accordance with the above setting function (c). This makes it possible to excavate the ground roughly quickly to some extent without any control, and thereafter proceed the excavation gradually in steps of several centimeters in such a manner as like carefully peeling off a thin skin, thus quickly digging up the target pipe without damaging it. Also, since the setting changeover switch 7c1 is pushed only when the numeral input setting is to be made through the numeral input switch 7b, the operator is just required to push the direct setting switch 7a when trying to make the direct teaching setting. Therefore, the setting changeover can be rationally achieved with a minimum switching operation and the area setting can be performed with priority given to the direct teaching setting. Moreover, when the setting changeover switch 7c1 is not pushed, the current position of the bucket end of the front device 1a is indicated on the display screen 7e, and when the setting changeover switch 7c1 is pushed, the setting mode is changed over and the numeral value input from the numeral input switch 7b is indicated on the display screen 7e. During the area limiting excavation control and the direct teaching setting, therefore, the operator can perform work while confirming the current position of the bucket end of the front device 1a on the display screen 7e. During the numeral input setting, the operator can proceed the setting while looking at the numeral value input from the numeral input switch 7b on the display screen 7e. In addition, whenever the area limiting excavation control is selected by pushing the area limiting switch 7d1, a value representing a position to which the front device cannot reach (- 20 m in the above example) is set as the initial value of the excavation area. This enables the front device to freely move over a full range where it is inherently operable, for free setting of the excavation area within that full operable range. A second embodiment of the present invention will be described with reference to Figs. 11 and 12. In this embodiment, the present invention is applied to a hydraulic excavator employing electric control lever units. Referring to Fig. 11, a hydraulic excavator in which this embodiment is realized includes electric control lever units 14a - 14f instead of the foregoing control lever units 4a - 4f of pilot hydraulic type. The control lever units 14a - 14f each output, as an electric signal, a voltage depending on the input amount and the direction by and in which their control levers are each manipulated by the operator, and supply the electric signal to corresponding one of electro-hydraulic converting means, e.g., solenoid driving sectors 30a, 30b - 35a, 35b including proportional solenoid valves, provided at opposite ends of the flow control valves 15a - 15f through a control unit 9A. A setting device 7 is the same as that used in the first embodiment shown in Fig. 3. Fig. 12 shows control functions of the control unit 9A. The control unit 9A includes various functions executed by a front posture calculating portion 9a, an area setting calculating portion 9b, a bucket end speed limit value calculating portion 9c, an arm cylinder speed calculating portion 9Ad, an arm-dependent bucket end speed calculating portion 9e, a boom-dependent bucket end speed limit value calculating portion 9f, a boom cylinder speed limit value calculating portion 9g, a boom command limit value calculating portion 9Ah, a boom command adjustment calculating portion 9j, a boom command calculating portion 9Ai, an arm command calculating portion 9k, and a display changeover control calculating portion 9s. The arm cylinder speed calculating portion 9Ad determines a displacement of the arm cylinder through coordinate transformation based on the arm rotational angle detected by the angle sensor 8b, and differentiates the displacement, thereby directly deriving an arm cylinder speed. As an alternative, the arm cylinder speed may be derived by using the operation signal from the arm control lever unit 4b. The boom command limit value calculating portion 9Ah determines, based on the flow rate characteristic of the flow control valve 15a for the boom, a limit value of the boom command corresponding to the limit value of the boom cylinder speed determined in the calculating portion 9g. The boom command adjustment calculating portion 9j compares the limit value of the boom command determined in the calculating portion 9Ah with the command value from the control lever unit 14a and then outputs larger one when the area limiting switch 7d1 of the setting device 7 (see Fig. 3) is turned on (pushed) and the area limiting excavation control is selected, and it outputs the command value from the control lever unit 14a when the area limiting switch 7d1 is turned off (not pushed) and the area limiting excavation control is not selected. Here, as with the XaYa-coordinate system, the command value from the control lever unit 14a is defined to be positive (+) in the direction toward the inside of the set area from the outside of the set area (i.e., in the boom-up direction). Also, that the calculating portion 9j outputs larger one of the limit value of the boom command and the command value from the control lever unit 14a means that it outputs smaller one of absolute values of both the above values because the limit value c is negative (-) when the bucket end is inside the set area, and it outputs larger one of absolute values of both the above values because the limit value c is positive (+) when the bucket end is outside the set area. The boom command calculating portion 9Ai receives the command value from the boom command adjustment calculating portion 9j. When the received command value is positive, the calculating portion 9Ai outputs a corresponding voltage to the boom-up solenoid driving sector 30a of the flow control valve 15a and a voltage of 0 to the boom-down solenoid driving sector 30b thereof. When the received command value is negative, the calculating portion 9Ai outputs voltages in a reversed manner to the above. The arm command calculating portion 9k receives the command value from the control lever unit 14b. When the received command value is positive, the calculating portion 9Ai outputs a corresponding voltage to the arm-crowding solenoid driving sector 31a of the flow control valve 15b and a voltage of 0 to the arm-dumping solenoid driving sector 31b thereof. When the received command value is negative, the calculating portion 9k outputs voltages in a reversed manner to the above. Likewise, though not shown, valve command calculating portions are provided to receive respective command values from the control lever units 14c - 14f and output voltages corresponding to the received command values to the solenoid driving sectors of the associated flow control valves. The other functions are the same as those in the first embodiment. This embodiment thus constructed operates as follows. When the control lever of the boom control lever unit 14a is operated in the boom-down direction with the intention of positioning the bucket end, the command value from the control lever unit 14a is input to the boom command value adjustment calculating portion 9j. At the same time, the bucket end speed limit value calculating portion 9c calculates, based on the relationship shown in Fig. 7, a limit value a (< 0) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area, the boom-dependent bucket end speed limit value calculating portion 9f calculates a limit value c = a (< 0) of the boom-dependent bucket end speed, and the boom command limit value calculating portion 9Ah calculates a negative limit value of the boom command corresponding to the limit value c . Here, when the bucket end is far away from the boundary L of the set area, the limit value of the boom command determined in the calculating portion 9Ah is greater than the command value from the control lever unit 14a, and therefore the boom command value adjustment calculating portion 9j selects the command value from the control lever unit 14a. Since the selected command value is negative, the boom command calculating portion 9Ai outputs a corresponding voltage to the boom-down solenoid driving sector 30b of the flow control valve 15a, and a voltage of 0 to the boom-up solenoid driving sector 30a thereof. As a result, the boom is gradually moved down in accordance with the command value from the control lever unit 14a. As the boom is gradually moved down and the bucket end comes closer to the boundary L of the set area as mentioned above, the limit value c = a (< 0) of the, boom-dependent bucket end speed calculated in the calculating portion 9f is increased (its absolute value |a| or |c| is reduced). Then, when the corresponding boom command limit value determined in the calculating portion 9Ah becomes greater than the command value from the control lever unit 14a, the boom command value adjustment calculating portion 9j selects the former limit value and the boom command calculating portion 9Ai gradually restricts the voltage output to the boom-down solenoid driving sector 30b of the flow control valve 15a depending on the limit value c . Accordingly, the boom-down speed is gradually restricted as the bucket end comes closer to the boundary L of the set area, and the boom is stopped when the bucket end reaches the boundary L of the set area. As a result, the bucket end can be easily and smoothly positioned. Because of the above modifying process being carried out as speed control, if the speed of the front device 1A is extremely large, or if the control lever unit 14a is abruptly manipulated, the bucket end may go out beyond the boundary L of the set area due to a response delay in the control process, e.g., a delay in the hydraulic circuit, inertial force imposed upon the front device 1A, and so on. When the bucket end has moved out beyond the boundary L of the set area, the limit value a (= c ) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area is calculated as a positive value in the calculating portion 9c based on the relationship shown in Fig. 7, and the boom command calculating portion 9Ai outputs a voltage corresponding to the limit value c to the boom-up solenoid driving sector 30a of the flow control valve 15a. The boom is thereby moved in the boom-up direction at a speed proportional to the distance D for restoration toward the inside of the set area, and then stopped when the bucket end is returned to the boundary L of the set area. As a result, the bucket end can be more smoothly positioned. Further, when the control lever of the arm control lever unit 14b is operated in the arm-crowding direction with the intention of digging the ground toward the body, the command value from the control lever unit 14b is input to the arm command calculating portion 9k which outputs a corresponding voltage to the arm-crowding solenoid driving sector 31a of the flow control valve 15b, causing the arm to be moved down toward the body. At the same time, the command value from the control lever unit 14b is also input to the arm cylinder speed calculating portion 9Ad which calculates an arm cylinder speed. Then, the arm-dependent bucket end speed calculating portion 9e calculates an arm-dependent bucket end speed b. On the other hand, the bucket end speed limit value calculating portion 9c calculates, based on the relationship shown in Fig. 7, a limit value a (< 0) of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area, and the boom-dependent bucket end speed limit value calculating portion 9f calculates a limit value c = a - b y of the boom-dependent bucket end speed. Here, when the bucket end is so far away from the boundary L of the set area as to meet the relationship of a < b y (|a| > |b y |), the limit value c is calculated as a negative value in the calculating portion 9f. Therefore, the boom command value adjustment calculating portion 9j selects the command value (= 0) from the control lever unit 14a and the boom command calculating portion 9Ai outputs a voltage of 0 to both the boom-up solenoid driving sector 30a and the boom-down solenoid driving sector 30b of the flow control valve 15a. The arm is thereby moved toward the body depending on the command value from the control lever unit 14b. As the arm is gradually moved toward the body and the bucket end comes closer to the boundary L of the set area as mentioned above, the limit value a of the bucket end speed calculated in the calculating portion 9c is increased (its absolute value |a| is reduced). Then, when the limit value a becomes greater than the component b y of the arm-dependent bucket end speed b vertical to the boundary L calculated in the calculating portion 9e, the limit value c = a - b y of the boom-dependent bucket end speed is calculated as a positive value in the calculating portion 9f. Therefore, the boom command value adjustment calculating portion 9j selects the limit value calculated in the calculating portion 9Ah, and the boom command calculating portion 9Ai outputs a voltage corresponding to the limit value c to the boom-up solenoid driving sector 30a of the flow control valve 15a. Thus, the bucket end speed is modified with the boom-up operation so that the component of the bucket end speed vertical to the boundary L is gradually restricted in proportion to the distance D to the bucket end from the boundary L. Accordingly, direction change control is carried out with a resultant of the unmodified component b x of the arm-dependent bucket end speed parallel to the boundary L and the speed component vertical to the boundary L modified depending on the limit value c , as shown in Fig. 9, enabling the excavation to be performed along the boundary L of the set area. Also, in this case, the bucket end may go out beyond the boundary L of the set area for the same reasons as mentioned above. When the bucket end has moved out beyond the boundary L of the set area, the limit value a of the bucket end speed in proportion to the distance D to the bucket end from the boundary L of the set area is calculated as a positive value in the calculating portion 9c based on the relationship shown in Fig. 7, the limit value c = a - b y (> 0) of the boom-dependent bucket end speed calculated in the calculating portion 9f is increased in proportion to the limit value a , and the voltage output from the boom command calculating portion 9Ai to the boom-up solenoid driving sector 30a of the flow control valve 15a is increased depending on the limit value c . In the case of the bucket end having moved out of the set area, therefore, the boom-up operation for modifying the bucket end speed is performed so that the bucket end is restored toward the inside of the set area at a bucket end speed proportional to the distance D. Thus, the excavation is carried out under a resultant of the unmodified component b x of the arm-dependent bucket end speed parallel to the boundary L and the speed component vertical to the boundary L modified depending on the limit value c , enabling the excavation to be performed while the bucket end is gradually returned to and moved along the boundary L of the set area as shown in Fig. 10. Consequently, the excavation can be smoothly performed along the boundary L of the set area just by crowding the arm. With this embodiment, as described above, the area limiting excavation control can be similarly performed to the first embodiment in the control system employing electric control lever units. Also, similar advantages as with the first embodiment can also be obtained when the excavation area is set with the setting device 7 and the area setting calculating portion 9b. In the foregoing embodiments, the area limiting excavation control is started based on the initial value of the excavation area as soon as the area limiting switch 7d1 of the setting device 7 is pushed. However, the area limiting excavation control may be started only after the direct teaching setting or the numeral input setting is made. Fig. 13 shows, as a third embodiment of the present invention, such a modification. Fig. 13 corresponds to Fig. 12 representing the second embodiment. A boom command adjustment calculating portion 9Bj outputs the command value from the control lever unit 14a when the area limiting switch 7d1 is turned off (not pushed and the area limiting excavation control is not selected. Even when the area limiting switch 7d1 is turned on (pushed) and the area limiting excavation control is selected, the calculating portion 9Bj also outputs the command value from the control lever unit 14a if the direct setting switch 7a and the numeral value input switch 7b are not yet pushed. Then, if any one of the direct setting switch 7a and the numeral value input switch 7b is pushed and the excavation area is set in the condition where the area limiting switch 7d1 is turned on (pushed) and the area limiting excavation control is selected, the calculating portion 9Bj compares the limit value of the boom command determined in the calculating portion 9Ah with the command value from the control lever unit 14a and then outputs larger one. In the foregoing embodiments, when the area limiting switch 7d1 of the setting device 7 is turned off to bring the area limiting excavation control to an end, the excavation are is always reset to the initial value Y = -20 m. However, the control unit 9 may store the values set until that time and start the control process from the previous set value of the excavation area when the control process is resumed subsequently. Fig. 14 shows, as a fourth embodiment of the present invention, such a modification. Fig. 14 corresponds to Fig. 6 representing the first embodiment. After the area limiting switch 7d1 is turned off in step 240, the value set up to that time is stored in step 250C for each control process. Then, when the next control process is started, the previous set value is used as a set value of the excavation area in step 120C. In the foregoing embodiments, the value set by the direct teaching is used as the base value from which the value input by the numeral input setting is increased or reduced. However, the base value from which the value input by the numeral input setting is increased or reduced may be always held constant (e.g., at a fixed base value of Y = 0). Fig. 15 shows, as a fifth embodiment of the present invention, such a modification. Fig. 15 also corresponds to Fig. 6 representing the first embodiment. Changes input by the numeral input setting are directly set as set values = dY2, dY3, dY4, respectively, in steps 180D, 200D, 230D. Alternatively, the base value from which the value input by the numeral input setting is increased or reduced may be set to the height of the pivot point of the boom 1a from the ground surface. This case is advantageous in that the value input by the numeral input setting provides a depth from the ground surface. Another example of the setting device for use in the front control system will be described, as a sixth embodiment of the present invention, with reference to Fig. 16. In Fig. 16, denoted by 500 is a box-type control panel constituting the setting device. The control panel 500 has various switches such as a main switch 501, a direct setting switch 502, an up-switch 503a and a down-switch 503b for the numeral input setting, a low-speed mode switch 504, a display changeover switch 505 and a 0-setting switch 506, various LED's 510 - 516 associated with these switches, a warm-up alarm lamp 517, and a liquid crystal display screen 520. These components are mounted on a panel body 530. The main switch 501 is to select whether the area limiting excavation control according to the present invention is started or not, and corresponds to the area limiting switch 7d1 shown in Fig. 3. When the main switch 501 is pushed (turned on), a control start signal instructing changeover from a normal mode to an area limiting excavation control is output to the control unit 9, thus making it possible to perform, e.g., the setting of the excavation area and the area limiting excavation control described in connection with the first embodiment. At the same time, the LED 510 is lit up to inform the operator of that the area limiting excavation control mode is now selected. The direct setting switch 502 is to set an excavation area by the direct teaching and corresponds to the direct setting switch 7a shown in Fig. 3. When the switch 502 is pushed, a direct teaching setting signal is output to the control unit 9, whereupon, as described before, the position of a predetermined part, e.g., the end of the bucket 1c, of the front device 1A at that time is calculated and the excavation area is set based on the calculated value. At the same time, the LED 511 is lit up to inform the operator of that the excavation area is being set. The up-switch 503a and the down-switch 503b for the numeral input setting are to set an excavation area by inputting a numeral value and corresponds to the up-key 7b1 and the down-key 7b2 shown in Fig. 3. When any one of these switches is pushed, a numeral value is increased or reduced in unit of a predetermined amount with 0, for example, as a base, and the input value is indicated on the liquid crystal display screen 520. Also, the input value is applied as a numeral input setting signal to the control unit 9 and the excavation area is set in accordance with the input value. At the same time the LED 511 is lit up to inform the operator of that the excavation area is being set. Pushing the up-switch 503a increases the numeral value and pushing the down-switch 503b reduces the numeral value. The low-speed mode switch 504 is to select whether the area limiting excavation control described in connection with the first embodiment, for example, is to be performed in a speed preference work mode or an accuracy preference work mode. When the mode switch 504 is not pushed and kept turned off, the speed preference work mode is selected and the area limiting excavation control can be efficiently performed by using the detection signals from the pressure sensors 61a, 61b. When the mode switch 504 is pushed and turned on, the accuracy preference work mode is selected so that the detection signals from the pressure sensors 61a, 61b are reduced in level and the area limiting excavation control can be precisely performed by using the reduced values. The display changeover switch 505 is to change over the data indicated on the liquid crystal display screen 520 and corresponds to the setting changeover switch 7c1 shown in Fig. 3. When the switch 505 is pushed to select "DEPTH" shown in Fig. 16, the LED 513 is lit up and the depth (or height) of the end position of the bucket 1c calculated in the control unit 9 is indicated on the liquid crystal display screen 520. When it is pushed to select "BUCKET ANGLE", the LED 514 is lit up and the angle of the bucket 1c calculated in the control unit 9 is indicated on the liquid crystal display screen 520. When it is pushed to select "TRANSVERSE TILT", the LED 515 is lit up and the tilt angle of the body 1B (see Fig. 2) in the transverse direction is indicated on the liquid crystal display screen 520. When it is pushed to select "NUMERAL SETTING", the LED 516 is lit up and the excavation area can be set by inputting a numeral value through the up-switch 503a and the down-switch 503b. The 0-setting switch 506 is to set a base for an input value when "DEPTH" and "BUCKET ANGLE" are selected by the display changeover switch 505. When the switch 506 is not pushed and kept turned off, the depth is calculated and indicated with the level of the body 1B on the ground surface as a base (0) for "DEPTH", and the angle is calculated and indicated with the horizontal direction as a base (0) for "BUCKET ANGLE". When the switch 506 is pushed and turned on, the depth is calculated and indicated with the end position of the bucket at that time as a base for "DEPTH", and the angle is calculated and indicated with the direction of the bucket at that time as a base for "BUCKET ANGLE". The warm-up alarm lamp 517 is to indicate a temperature condition of hydraulic oil (fluid), and is controlled to light up or turn out by the control unit 9 in accordance with a signal from a oil temperature sensor 13. For example, the control unit 9 determines in which one of three oil temperature ranges, i.e., a first oil temperature range, a second oil temperature range higher than the first oil temperature range, and a third oil temperature range higher than the second oil temperature range, the temperature of the hydraulic oil detected by the oil temperature sensor 13 falls. When the temperature of the hydraulic oil is in the third oil temperature range, the warm-up alarm lamp 517 is not lit up. When the temperature of the hydraulic oil is in the second oil temperature range, the warm-up alarm lamp 517 blinks. When the temperature of the hydraulic oil is in the first oil temperature range, the warm-up alarm lamp 517 is lit up continuously and the area limiting control is forcibly ceased. This enables the operator to recognize in which one of the three regions the oil temperature falls currently, and to perform the area limiting excavation control precisely and safely. With this embodiment thus constructed, the operator can not only easily perform the operation of changing over the control mode and the area setting operation by using the control panel 500, but also obtain necessary information about the position and posture of the bucket. Further, it is possible for the operator to know the current condition of the oil temperature exactly by looking at the warm-up alarm lamp 517 on the control panel 500, and to perform the area limiting excavation control precisely and safely. A seventh embodiment of the present invention will be described with reference to Figs. 17 to 20. This embodiment intends to temporarily cancel the front control by using a temporary cancel switch and simply resume the front control after temporary cancellation. In Figs. 17 to 20, equivalent members or functions to those in Figs. 1 and 4 are denoted by the same reference numerals. Referring to Fig. 17, a front control system of this embodiment further comprises, in addition to the components of the first embodiment, a second direct setting switch 70a for setting by the direct teaching an excavation area where the end of the bucket 1c is allowed to move, and a temporary cancel switch 70b for instructing temporary cancellation of the area limiting excavation control. Signals from these switches 70a, 70b are input to a control unit 9E along with the signals explained before in connection with the first embodiment. As shown in Fig. 18, the direct setting switch 70a and the temporary cancel switch 70b are installed on a grip 70 of the control lever 40a of the boom control lever unit 4a. The direct setting switch 70a is a momentarily-operated switch which is turned on only while it is pushed by the operator. When the direct setting switch 70a is pushed, an area setting signal is output to the control unit 9E to instruct that the excavation area is to be set or updated by the direct teaching, for example, as with the direct setting switch 7a shown in Fig. 3. The temporary cancel switch 70b is also a momentarily-operated switch which is turned on only while it is pushed by the operator. While the temporary cancel switch 70b is kept pushed, the area limiting excavation control is temporarily cancelled, bringing back the front control system to a normal excavation state. Further, the two switches 70a, 70b have surface configurations different from each other, allowing the operator to discern the difference between the switches just by touching them by a finger. In the above, the control lever units 4a - 4d have been denoted by separate reference numerals corresponding to the boom, the arm, the bucket and the upper structure (swing motor). In practice, however, the boom control lever unit 4a and the bucket control lever unit 4c are constructed as a single control lever unit, and the arm control lever unit 4b and the swing control lever unit 4d are also constructed as a single control lever unit. Then, by manipulating each control lever of the control lever units two-dimensionally, operation signals (pilot pressures) for the boom and/or the bucket and the arm and/or the upper structure are output. Fig. 19 shows control functions of the control unit 9E. The control functions of the control unit 9E are the same as those of the control unit 9 in the first embodiment except that an area setting calculating portion 9Eb and an area limiting control changeover calculating portion 9Er differ in the points below from the area setting calculating portion 9b and the area limiting control changeover calculating portion 9r shown in Fig. 4. The area setting calculating portion 9Eb executes calculation for setting an excavation area where the end of the bucket 1c is allowed to move, in accordance with any one of the direct teaching setting using the direct setting switch 7a of the setting device 7 shown in Fig. 3 and the numeral input setting using the numeral input switch 7b thereof, and the direct teaching setting using the direct setting switch 70a on the control lever 40a. More specifically, in this embodiment, the excavation area can be set by the direct teaching with any of the two switches, i.e., the direct setting switch 7a of the setting device 7 and the direct setting switch 70a on the control lever 40a. The processing steps executed in the area setting calculating portion 9Eb upon the direct setting switch 70a being pushed is the same as those executed upon the direct setting switch 7a being pushed. The processing steps are executed following the flowchart shown in Fig. 6, for example, though "7a" is replaced by "70a". Other than being shown in Fig. 6, the processing steps may be executed following the flowchart shown in Fig. 14 or 15. The area limiting control changeover calculating portion 9Er selectively outputs the value calculated in the calculating portion 9h in accordance with turning-on or -off of signals from the area limiting switch 7d1 and the temporary cancel switch 70b. This process is detailed in a flowchart of Fig. 20. Referring to Fig. 20, when the area limiting switch 7d1 is turned on (pushed) to instruct the start of the area limiting excavation control and the temporary cancel switch 70b is turned off (not pushed) not to instruct temporary cancellation of the control, the value calculated in the calculating portion 9h is output directly as the limit value of the boom pilot pressure (step 300 → 310 → 320). When the area limiting switch 7d1 is turned off (not pushed) not to instruct the start of the area limiting excavation control or when the temporary cancel switch 70b is turned on (pushed) to instruct temporary cancellation of the control, a maximum value is output as the limit value of the boom pilot pressure (step 300 → 320 or 310 → 330). In this embodiment thus constructed, the operation performed under the area limiting excavation control with the area limiting switch 7d1 turned on and the temporary cancel switch 70b turned on is the same as that performed in the first embodiment with the area limiting switch 7d1 turned on. When the operator wants to temporarily cancel the area limiting excavation control during the operation under the area limiting excavation control, the operator turns on (pushes) the temporary cancel switch 70b on the grip 70 of the control lever 40a of the boom control lever unit 4a. Upon the temporary cancel switch 70b being pushed, the area limiting control changeover calculating portion 9r outputs, as the limit value of the boom pilot pressure, the maximum value rather than the value calculated in the calculating portion 9h, and the output value is applied to the boom command calculating portion 9i while the switch 70b is kept pushed. Therefore, the calculation process executed in the calculating portions 9a - 9h for the area limiting excavation control is made infeasible to cancel the control being executed. After that, when the operator releases his finger from the temporary cancel switch 70b, the switch 70b is turned off, whereupon the area limiting control changeover calculating portion 9r outputs, as the limit value of the boom pilot pressure, the value calculated in the calculating portion 9h so that the area limiting excavation control is simply resumed without setting the area limiting excavation control again. With this embodiment, as described above, since the temporary cancel switch 70b is provided, an excavation mode can be easily changed over between the excavation under the normal control and the excavation under the area limiting control. It is thus possible to quickly and smoothly perform digging work requiring a combination of the normal excavation and the excavation under the area limiting control, such as work of burying a water service pipe or the like in the ground by alternately repeating trench digging for which the excavation under the area limiting control is more convenient and pipe installation for which the normal excavation is more convenient. Also, since the temporary cancel switch 70b is provided on the grip 70 of the control lever 40a of the boom control lever unit 4a, the operator can promptly change over the normal excavation and the excavation under the area limiting control from one to the other without releasing his hand from the control lever. Further, since not only the temporary cancel switch 70b but also the direct setting switch 70a are provided on the grip 70 of the control lever 40a of the boom control lever unit 4a, the operator can also promptly set the excavation area without releasing his hand from the control lever, even when trying to set the excavation area by the direct teaching. This makes the operator not feel troublesome in setting the excavation area. Moreover, since the direct setting switch 70a is provided on the control lever 40a of the boom control lever unit 4a which instructs the vertical movement of the front device 1A, the operator can push the direct setting switch 70a to set the area with his one hand while manipulating the control lever 40a to move the boom with the same hand. As a result, the height can be easily adjusted in setting the area and the delicate setting is facilitated. Additionally, the direct setting switch 70a and the temporary cancel switch 70b are both installed on the same control lever, but their surface configurations are different from each other. Therefore, the operator can discern the respective functions of the two switches just by touching them without visually confirming the switches, resulting in quicker and smoother operation. While the direct setting switches 7a, 70a are provided respectively on the setting device 7 and the control lever 40a in the above embodiment, only one of the direct setting switches 7a, 70a may be provided. An eighth embodiment of the present invention will be described with reference to Figs. 21 to 22. In Figs. 21 to 22, equivalent functions to those in Figs. 1 and 19 are denoted by the same reference numerals. This embodiment intends to temporarily cancel the front control in a different manner from the seventh embodiment when the temporary cancel switch is pushed. Referring to Fig. 21, in an area setting calculating portion 9Fb, the set value of the excavation area is temporarily initialized while the temporary cancel switch 70b is kept pushed, and when the temporary cancel switch 70b is released, the set value is restored to the value before the temporary cancel switch 70b is pushed. This process is detailed in a flowchart of Fig. 22. Referring to Fig. 22, when the area limiting switch 7d1 is turned on (pushed), a value representing a position to which the front device cannot reach, e.g., Y = - 20 m as mentioned above, is set as the initial value of the boundary L (depth h 1 ) of the excavation area, and this value is stored (steps 400 → 410). Then, the boundary L of the excavation area is set as follows depending on which one of the direct setting switch 70a and the temporary cancel switch 70b is pushed. (a) When Direct Setting Switch 70a is Pushed When the operator pushes the direct setting switch 70a after moving the end P 1 of the bucket 1c to a target position, the boundary L of the excavation area is set below by using the Y-coordinate value, Y = Y 1 , of the bucket end P 1 calculated in the front posture calculating portion 9a at that time; set value = Y-coordinate value Y 1 and the set value is stored (steps 420 → 421 → 422 → 430 → 440 → 450 → 420). (b) When Temporary Cancel Switch 70b is Being Pushed When the temporary interrupt switch 70b is pushed, the same value as the initial value set upon the area limiting switch 7d1 being pushed, i.e., the value (- 20 m) representing a position to which the front device cannot reach, is set as the boundary L of the excavation area (steps 430 → 431 → 450 → 420 → 430). But the set value is not stored. (c) When Temporary Cancel Switch 70b is Released (Turned off) When the operator releases his finger from the temporary cancel switch 70b (to turn off it), the stored value is invoked to set the boundary L of the excavation area below; set value = stored set value (steps 430 → 440 → 450 → 420 → 430). When bringing the area limiting excavation control to an end, the area limiting switch 7d1 is pushed again to be turned off (step 450). Then, the boundary L of the excavation area is set to the initial value Y = - 20 m again for safety (step 460), followed by ending the front control. As described above, the area limiting excavation control can also be made essentially infeasible and cancelled for a while by setting the value (- 20 m) representing a position to which the front device cannot reach, as the boundary L of the excavation area, and initializing the set value temporarily. This embodiment can also provide similar advantages as obtainable with the above embodiment. While typical several embodiments of the present invention have been described hereinabove, the present invention is not limited to those embodiments, but may be modified in various manners. The following is several examples of modification. (1) The angle sensors for detecting the rotational angles of the front members as means for detecting the status variables relating to the position and posture of the front device 1A. But cylinder strokes may be detected instead of the rotational angles. (2) The distance D to the bucket end from the boundary L of the set area is employed for the area limiting excavation control. From the viewpoint of implementing the invention in a simpler way, however, the distance to a pin at the arm end from the boundary of the set area may be employed instead. Further, when an area is set for the purpose of preventing interference of the front device with other members and ensuring safety, a predetermined part of the front device may be any other part giving rise to such interference. (3) While the hydraulic drive system to which the present invention is applied has been described as a closed center system including the flow control valves of closed center type, the invention is also applicable to an open center system including flow control valves of open center type. (4) The temporary cancel switch is in the form of a momentarily-operated switch which is turned on only while it is pushed by the operator, but may be an alternately-operated switch which is kept turned on once pushed, making the front control continue to be cancelled, and is turned off when pushed again, allowing the front control to resume. (5) While the temporary cancel switch is provided on the boom control lever, it may be provided on the arm control lever. (6) While the embodiments including the temporary cancel switch have been described as employing the control lever units of hydraulic pilot type, electric control lever units may be employed instead.

Claims: Construction machine comprising a multi-articulated front device (1A) made up of a plurality of front members (1a-1c) rotatable in the vertical direction, a plurality of hydraulic actuators (3a-3c) for driving respectively said plurality of front members (1a-1c), a plurality of hydraulic control valves (5a-5f) driven in accordance with respective operation signals input from a plurality of operating means (4a-4f) for controlling flow rates of a hydraulic fluid supplied to said plurality of hydraulic actuators, and a front control system for controlling said front device (1A) to be moved in a preset area, wherein said front control system comprises: first area setting means having a direct setting switch (7a) for setting an area where said front device (1A) is allowed to move, by direct teaching in response to an instruction from said direct setting switch (7a), second area setting means having a numeral input switch (7b) for setting an area where said front device (1A) is allowed to move, by inputting a numeral value through said numeral input switch (7b), and setting selection means for selecting one of said first area setting means and said second area setting means, characterized in that the front control system further comprises display means (7e) and display changeover means for instructing said display means (7e) to display a current position of said front device (1A) when said first area setting means is selected, and instructing said display means (7e) to display the numeral value input through said numeral input switch (7b) of said second area setting means when said second area setting means is selected. Construction machine according to Claim 1, characterized in that said setting selection means has a setting changeover switch (7c1) for enabling one of said first area setting means and said second area setting means to be selected when said setting changeover switch (7c1) is not operated, and enabling the other of said first area setting means and said second area setting means to be selected when said setting changeover switch (7c1) is operated. Construction machine according to Claim 1 or 2, characterized in that said setting selection means enables said first area setting means to be selected regardless of whether said setting changeover switch (7c1) is operated or not, when said direct setting switch (7a) of said first area setting means is operated, and enables said second area setting means to be selected when said setting changeover switch (7c1) is operated. Construction machine according to one of the Claims 1 to 3, characterized in that said numeral input switch (7b) of said second area setting means comprises a first numeral input key (7b1) for increasing an input numeral value from a certain base value, and a second numeral input key (7b2) for reducing an input numeral value from a certain base value. Construction machine according to one of the Claims 1 to 4, characterized in that said second area setting means previously sets, as an initial value, a value representing a position to which said front device (1A) cannot reach, and changes a set numeral value through said numeral input switch (7b) with said initial value as a base, thereby setting said area. Construction machine according to one of the Claims 1 to 5, characterized in that said second area setting means changes a set numeral value through said numeral input switch (7b) with the numeral value set by said direct teaching as a base, thereby setting said area. Construction machine according to one of the Claims 1 to 6, characterized in that said second area setting means changes a set numeral value through said numeral input switch (7b) with the previous set numeral value as a base, thereby setting said area. Construction machine according to one of the Claims 1 to 7, characterized in that the construction machine further comprises a control selection switch for selecting whether said front device (1A) is to be controlled or not, and initializing means for setting, as an initial value of the area to be set, a value representing a position to which said front device cannot reach, each time when said control selection switch is operated for selection of front control. Construction machine according to Claim 1, characterized by control means for controlling the operation of said front device (1A) by modifying said operation signal so that said front device is allowed to move within an area set by one of said first area setting means and said second area setting means, a temporary cancel switch, and control cancel means for temporarily cancelling control of said front device performed by said control means when said temporary cancel switch is pushed. Construction machine according to Claim 9, characterized in that said temporary cancel switch is provided on a lever grip of one of a plurality of control lever means. Construction machine according to Claim 10 or 11, characterized in that said direct setting switch (7a) and said numeral input switch (7b) are provided on a box-type control panel (7) installed in a cab, and said temporary cancel switch is provided on a lever grip (70) of one of said plurality of control lever means (4a-4f). Construction machine according to Claim 12, characterized in that said first area setting means further includes another direct setting switch provided on said lever grip for direct setting of the area where said front device is allowed to move. Construction machine according to Claim 13, characterized in that temporary cancel switch and said direct setting switch both provided on said lever grip have surface configurations different from each other. Construction machine according to Claim 11 or 12, characterized in that said control lever means on which said temporary cancel switch is provided is the control lever means for a boom of a hydraulic excavator. Construction machine according to Claim 10, characterized in that said control cancel means is means for interrupting modification of the operation signal made by said control means when said temporary cancel switch is pushed. Construction machine according to Claim 10, characterized in that said control cancel means is means for temporarily changing the set position of a boundary of said area to a value representing a position to which said front device cannot reach, when said temporary cancel switch is pushed. Control panel for a construction machine comprising a multi-articulated front device (1A) made up of a plurality of front members (1a-1c) rotatable in the vertical direction, a plurality of hydraulic actuators (3a-3c) for driving respectively said plurality of front members, a plurality of hydraulic control valves (5a-5f) driven in accordance with respective operation signals input from a plurality of operating means (4a-4f) for controlling flow rates of a hydraulic fluid supplied to said plurality of hydraulic actuators (3a-3c), and a front control system controlling said front device (1A) to be moved in a preset area, wherein said control panel (500) comprises: a direct setting switch (502) for instructing said front control system, by direct teaching, setting of an area where said front device (1A) is allowed to move, a numeral input switch (503) for instructing said front control system by input of a numeral value, setting of an area where said front device (1A) is allowed to move, and setting changeover switch for selecting one of the setting instructions from said direct setting switch (502) and said numeral input switch (503), characterized by display means (520) for displaying a current position of said front device (1A) when said setting changeover switch is not operated, and displaying the numeral value input through said numeral input switch (7b) when said setting changeover switch is operated. Control panel according to Claim 17, characterized in that said numeral input switch (503) comprises a first numeral input key (503a) for increasing an input numeral value from a certain base value, and a second numeral input key (503b) for reducing an input numeral value from a certain base value. Control panel according to Claim 18, characterized by a control selection switch for selecting whether said front device (1A) is to be controlled or not, whereby selection of the control of said front device by said control selection switch enables said direct setting switch (502) and said numeral input switch (503) to instruct the setting.

Inventors: FUJISHIMA KAZUO, HAGA MASAKAZU, NAKAGAWA TAKASHI, WATANABE HIROSHI, FUJISHIMA, KAZUO, HAGA, MASAKAZU, NAKAGAWA, TAKASHI, WATANABE, HIROSHI, Fujishima, Kazuo, c/o Hitachikenki Tsukuba-ryo, Nakagawa, Takashi, c/o Hitachikenki Tsukuba-ryo
Applicants: HITACHI CONSTRUCTION MACHINERY, HITACHI CONSTRUCTION MACHINERY CO., LTD.
Application year: 1997
Main classification: E02F3
IPC codes: E02F9, E02F3