How correctly move joints by SetPositionPID() and SetPositionTarget()

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I want to set a joint to a certain angle properly and get its torque using Joint::GetForceTorque() in the process.

So I follow this tutorials try to control a joint, I try SetPositionPID() and SetPositionTarget() to contorl a joint ,but when I do this the joint cannt stop even its PID be set to zero by SetPositionPID(name, common::PID(0, 0, 0)).

P.S. I am using Gazebo-8, WITHOUT ROS. I have added (part of) the code from my plugin below.

    std::string name;
    if (update_num == 0)
    {

        //Joint velocity using PID controller
        this->jointController.reset(new physics::JointController(this->model));
        this->jointController->AddJoint(model->GetJoint("purple_joint"));
        name = model->GetJoint("purple_joint")->GetScopedName();
        //          this->jointController->SetVelocityPID(name, common::PID(100, 0, 0));
        this->jointController->SetPositionPID(name, common::PID(100, 0, 0));
        this->jointController->SetPositionTarget(name,1.57);
        //          this->jointController->SetVelocityTarget(name, 1.0);

    }
    else if (update_num < 200)
    {
        // Must update PID controllers so they apply forces
        this->jointController->Update();
    }
    else if (update_num >= 200)
    {
        name = model->GetJoint("purple_joint")->GetScopedName();
        this->jointController->SetPositionPID(name, common::PID(0, 0, 0));
        this->jointController->SetPositionTarget(name,0);

    }
    update_num++;

Is there something wrong and why? How to set a joint to a certain angle properly and get its torque using Joint::GetForceTorque() in this process?

Best Regards!

xinaxjm