Glass ribbon width control method in float process

A method for controlling the width of a glass ribbon in a float process of flat glass production in which a molten glass is poured through a tweel onto a molten metal in a bath to form a glass ribbon floating and advancing on the molten metal bath, the method comprising:

• detecting the width of the glass ribbon at a location remote from the tweel,
• comparing the detected width with a predetermined standard and generating an error signal representing the error therebetween,
• discriminating between a first case where said error signal is within a predetermined range of the error and a second case where said error signal is outside said range,
• generating a first control signal from said error signal in accordance with an integral control mode in the case of said first case and generating a second control signal from said error signal in accordance with a proportional-plus-integral control mode of a sampled data system in the case of said second case, and
• regulating the tweel to manipulate the rate of supplying a molten glass to the bath under command of said first control signal in the case of said first case and under command of said second control signal in the case of said second case in such a manner as to maintain the glass ribbon width uniform.