计算图示机构的自由度，若含有复合铰链、局部自由度和虚约束请明确指出。<br /> <img src="https://nimg.ppkao.com/2019-05/wangjing/2019051414213830277.jpg?sign=ab0cf6327e3aa9c44bb807d52450cef0&t=62d74074" />