Work machine

1. A work machine comprising:

a multi-joint type work implement;

a plurality of hydraulic actuators driving the work implement;

an operation device outputting an operation signal to the plurality of hydraulic actuators;

a storage section storing a target configuration defined by connecting a plurality of target surfaces;

a control object surface selection section that uses a target surface closest to a control point set at a forward end portion of the work implement on the target configuration as a control object surface; and

a target operation control section that when an excavation operation is input from an operator via the operation device, controls the plurality of hydraulic actuators such that operational range of the control point is limited to the control object surface and a region above the control object surface, wherein

the control object surface selection section is configured to

determine whether or not a point closest to the control point on the target configuration is an inflection point when the control point is on the target configuration or in the region above the target configuration, and

use as the control object surface an imaginary plane passing an inflection point on the target configuration corresponding to the inflection point when it is determined that a point closest to the control point is an inflection point and when the inflection point is a top of slope.

2. The work machine according to claim 1 , further comprising a setback configuration generating section generating a setback configuration obtained by connecting a plurality of selection reference surfaces set back downwardly the plurality of target surfaces constituting the target configuration, wherein

the storage section stores a control line which is a segment extracted from contour of a forward end portion of the work implement and previously set and in which the control point is set, and

the control object surface selection section is configured to

when a part or entirety of the control line is situated under the setback configuration and when both ends of the control line are on the setback configuration or in a region above the setback configuration,

select from among a plurality of inflection points constituting the setback configuration an inflection point a foot of a vertical line extending from which to the control line is situated on the control line, the vertical line extending from which is under the setback configuration, and length of the vertical line extending from which is maximum, and

use as the control object surface an imaginary plane passing the inflection point on the target configuration corresponding to the selected inflection point.

3. The work machine according to claim 1 , further comprising a setback configuration generating section generating a setback configuration obtained by connecting a plurality of selection reference surfaces set back downwardly the plurality of target surfaces constituting the target configuration, wherein

the storage section stores a control line which is a segment extracted from contour of a forward end portion of the work implement and previously set and in which the control point is set, and

the control object surface selection surface is configured to

determine whether or not a point closest to the control point on the setback configuration is an inflection point when a part or entirety of the control line is under the setback configuration and when both ends of the control line are not on the setback configuration or in the region above the setback configuration,

use as the control object surface a target surface corresponding to the selection reference surface of the two selection reference surfaces connected to the inflection point closer to the control point when it is determined in the determination that a point closest to the control point is an inflection point and when the inflection point is a foot of slope, and

use as the control object surface a target surface corresponding to the selection reference surface closest to the control point on the setback configuration when it is determined in the determination that a point closest to the control point is an inflection point and when the inflection point is not a foot of slope, or when it is determined in the determination that a point closest to the control point is not an inflection point.

4. The work machine according to claim 1 , further comprising a setback configuration generating section generating a setback configuration obtained by connecting a plurality of selection reference surfaces set back downwardly the plurality of target surfaces constituting the target configuration, wherein

the storage section stores a control line which is a segment extracted from contour of a forward end portion of the work implement and previously set and in which the control point is set, and

the control object surface selection section is configured to

determine whether or not a point closet to the control point on the setback configuration is an inflection point when a part or entirety of the control line is not under the setback configuration,

use as the control object plane an imaginary plane passing an inflection point on the target configuration corresponding to the inflection point when it is determined in the determination that a point closest to the control point is an inflection point and when the inflection point is a top of slope, and

use as the control object surface a target surface corresponding to the selection reference surface closest to the control point on the setback configuration when it is determined in the determination that a point closest to the control point is an inflection point and when the inflection point is not a top of slope, or when it is determined in the determination that a point closest to the control point is not an inflection point.