简述开环控制数控机床、半闭环控制数控机床及闭环控制数控机床的概念及特点。

数控机床按照伺服控制方式分类，可以分为（）、半闭环数控机床、闭环数控机床。

数控机床的控制系统分为（）控制系统、闭环控制系统和半闭环控制系统三种。

Every deliberate act of wrongdoing by the master or any of the crew against the ship or cargo，without the authorization or privity of the Shipowner or his agent，is（）.

（）, or drum is used for hauling in or letting out the wires or ropes which will fasten the ship to the shore.

A salvor may be（）the whole or part of the payment due under Salvage Convention to the extent that the salvage operations have become necessary or more difficult because of fault or neglect on his part or if the salvor has been guilty of fraud or other dishonest conduct.

The （） is used for hauling in or letting out the wires or ropes.

Vessels must be（）valid certificate of nationality or certificated of registry or license.

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。

数控车床按控制方式分类有开环控制系统，半闭环控制系统。

数控机床按控制系统的特点可分为开环、闭环和半闭环系统。（）

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。