A controller assembly for a first drive shaft and a second drive shaft, said controller assembly comprising: a housing; a first tube unit having a first outer threaded surface, and rotatably retained in said housing, said first tube unit being coupled to be driven by the first drive shaft to rotate about a first axis which extends in a left-right direction; a second tube unit having a second outer threaded surface, and rotatably retained in said housing, said second tube unit being spaced apart from said first tube unit in a front-rear direction, and being coupled to be driven by the second drive shaft to rotate about a second axis which extends in the left-right direction; a first runner having a first inner threaded bore which is configured to be in threaded engagement with said first outer threaded surface of said first tube unit, said first runner being retained to slide along the first axis when said first tube unit is driven to rotate about the first axis; and a second runner having a second inner threaded bore which is configured to be in threaded engagement with said second outer threaded surface of said second tube unit, said second runner being retained to slide along the second axis when said second tube unit is driven to rotate about the second axis, said first and second runners (5, 6) being configured to be brought into abutment with each other in the left-right direction, such that in response to leftward sliding of said first runner to bring said first runner into abutment with said second runner, said first runner is prevented from sliding leftward over said second runner, whilst impeding rotation of said first tube unit, and such that in response to rightward sliding of said second runner to bring said second runner into abutment with said first runner, said second runner is prevented from sliding rightward over said first runner, whilst impeding rotation of said second tube unit, characterized in that said first runner is formed with a first stop tab extending in said front-rear direction (y) which has a leftward abutment surface, and said second runner is formed with a second stop tab extending in said front-rear direction (y) which has a rightward abutment surface, said leftward and rightward abutment surfaces (52, 62) being configured to be brought into abutment with each other in the left-right direction when said first and second runners (5, 6) are in abutment with each other. a housing; a first tube unit having a first outer threaded surface, and rotatably retained in said housing, said first tube unit being coupled to be driven by the first drive shaft to rotate about a first axis which extends in a left-right direction; a second tube unit having a second outer threaded surface, and rotatably retained in said housing, said second tube unit being spaced apart from said first tube unit in a front-rear direction, and being coupled to be driven by the second drive shaft to rotate about a second axis which extends in the left-right direction; a first runner having a first inner threaded bore which is configured to be in threaded engagement with said first outer threaded surface of said first tube unit, said first runner being retained to slide along the first axis when said first tube unit is driven to rotate about the first axis; and a second runner having a second inner threaded bore which is configured to be in threaded engagement with said second outer threaded surface of said second tube unit, said second runner being retained to slide along the second axis when said second tube unit is driven to rotate about the second axis, said first and second runners (5, 6) being configured to be brought into abutment with each other in the left-right direction, such that in response to leftward sliding of said first runner to bring said first runner into abutment with said second runner, said first runner is prevented from sliding leftward over said second runner, whilst impeding rotation of said first tube unit, and such that in response to rightward sliding of said second runner to bring said second runner into abutment with said first runner, said second runner is prevented from sliding rightward over said first runner, whilst impeding rotation of said second tube unit, characterized in that said first runner is formed with a first stop tab extending in said front-rear direction (y) which has a leftward abutment surface, and said second runner is formed with a second stop tab extending in said front-rear direction (y) which has a rightward abutment surface, said leftward and rightward abutment surfaces (52, 62) being configured to be brought into abutment with each other in the left-right direction when said first and second runners (5, 6) are in abutment with each other.