Control system for construction machine and control method

A control system for a construction machine equipped with a work implement and an operating device used to operate the work implement, the work implement having a boom, an arm, and a bucket, the control system comprising:

• a design plane setting unit configured to set a design plane indicating a target shape to be excavated;
• a target velocity determining unit configured to determine
• a boom target velocity in accordance with an operation amount of the operating device to operate the boom,
• an arm target velocity in accordance with an operation amount of the operating device device to operate the arm, and
• a bucket target velocity in accordance with an operation amount of the operating device device to operate the bucket;
• a distance obtaining unit configured to obtain a distance between a blade tip of the bucket and the design plane;
• a limit velocity determining unit configured to determine a limit velocity of an entirety of work implement based on the distance;
• a first limit determining unit configured to determine whether a first limit condition is satisfied;
• and
• a work implement control unit configured to control the work implement,
• the limit velocity determining unit being configured to determine a limit velocity of the boom from the limit velocity of the entirety of the entire work implement, the arm target velocity, and the bucket target velocity,
• the distance when the blade tip of the bucket is positioned outside of the design plane being a positive value and a velocity in a direction from inside of the design plane toward outside of the design plane being a positive value,
• the first limit condition including a condition that the limit velocity of the boom is greater than the boom target velocity, and
• the work implement control unit being configured to control the boom to match the limit velocity of the boom and to control the arm to match the arm target velocity when the first limit condition is satisfied.