1. Field of the Invention
The invention relates to a door opening and closing device for opening and closing a door of, for example, a numerical control (NC) machine by using a moving robot.
2. Description of Related Art
It is known that an NC machine is surrounded by a housing so as to prevent lubricating oil, chips, and similar materials from being scattered around during machining. The housing is provided with a large-sized sliding door so that the workpiece to be machined can be loaded into the housing and the machined workpiece removed from the housing using a robot.
The robot is an articulated robot, having a plurality of arms, and it is usually located in the vicinity of the door. A leading one of the arms is provided at its free end with a hand for gripping the workpiece. The workpiece to be machined is moved, by operating the arms, from the outside of the housing to a working position in the housing and the machined workpiece is moved again, by operating the arms, from the working position to the outside of the housing.
In moving the workpiece, using the arms of the articulated robot as mentioned above, it is necessary to open the sliding door to create an opening through which the workpiece and the arms can pass. A large-sized air cylinder is necessary for opening and closing the large-sized sliding door. If the articulated robot is operated to enter the housing under the condition where the sliding door is not sufficiently opened, there is a risk that the articulated robot will contact the sliding door. Accordingly, it is necessary to provide sensors for detecting opposite edges of the opening as defined by the open condition of the sliding door.
As mentioned above, in loading or unloading the workpiece into or from the housing, by operating the arms of the articulated robot, and machining the workpiece in the housing of the NC machine, it is necessary to open and close the large-sized sliding door and it is accordingly necessary to provide the large-sized air cylinder for driving the large-sized sliding door. Further, it is also necessary to provide a device for driving the large-sized air cylinder. In addition, it is necessary to provide at least two sensors for detecting the opposite edges of the opening defined by the open condition of the sliding door. For these reasons, the door opening and closing device in the prior art is complicated in construction and causes an increase in cost.
In addition, in such a device for opening and closing the sliding door by using an air cylinder, the operating speed of the sliding door and the positioning of the sliding door cannot be precisely controlled so that the period of time (cycle time) for loading and unloading of the workpiece by the articulated robot cannot be shortened.