Real robot move abnormal when connecting with moveit

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Hi, everyone! My robot arm was connected with MOVEIT by rosserialand I have succeed to bulid a hardware interface between them(JointStateInterface & VelocityJointInterface). But after I launch MOVEIT(demo.launch) , robot trembling at first, then keep moving until interference occurs.

1. Due to the limitation of sensor, I can't get a stable value of the robot. So I reduced the sensor resolution to 0.01. The graph below shows Fluctuation of readings.
2. I have tried to reverse motor rotation and get a same result.
3. When readings from robot dose not fluctuate, all cmd out put "0". As long as reading start to fluctuate, the value output from cmd will become biger and biger and will not decrease again.
4. I have tried to edit the value of PID but didn't work.No matter how much I reduce the value of I and D, it just makes the chaos comes a little later.
5. I have disable the simulation in demo.launch and sure that both ROS and hareware can get true value through the rosserial.

my hardware interface is here

How should I do to solve this problem? How can I control my robot with VelocityJointInterface? Thank you very much!