求助！！！新手急用！！怎样使用Quaternion.Slerp实现多次旋转？

我想使用
void FixedUpdate()
{
if(Direction == FingerGestures.SwipeDirection.Up)
{
target = Quaternion.Euler(transform.rotation.x+90,transform.rotation.y,transform.rotation.z);
transform.rotation = Quaternion.Slerp(transform.rotation,target,10*Time.fixedDeltaTime);
}
if(Direction == FingerGestures.SwipeDirection.Down)
{
target = Quaternion.Euler(transform.rotation.x-90,transform.rotation.y,transform.rotation.z);
transform.rotation = Quaternion.Slerp(transform.rotation,target,10*Time.fixedDeltaTime);
}
if(Direction == FingerGestures.SwipeDirection.Left)
{
target = Quaternion.Euler(transform.rotation.x,transform.rotation.y-90,transform.rotation.z);
transform.rotation = Quaternion.Slerp(transform.rotation,target,10*Time.fixedDeltaTime);
}
if(Direction == FingerGestures.SwipeDirection.Right)
{
target = Quaternion.Euler(transform.rotation.x,transform.rotation.y+90,transform.rotation.z);
transform.rotation = Quaternion.Slerp(transform.rotation,target,10*Time.fixedDeltaTime);
}
}
但是当我先向上滑动时向上转90度，然后向下滑却转了180度，就是说每次都是从最原始的位置开始旋转，为什么，怎么解决？