The author is aware of very large 3-
coordinate cutting machine available for import. Its three coordinates are p,a,z.To make
use of p,a,z and add another
coordinate e for turning angle control. The author finds that turning angle error cannot be avoided. So the author uses x, y,Z,θ as the 4 coordinates in her design of
4-coordinate cutting machine.The 4th coordinate θ is needed because torch must always be perpendicular to the surface at whichever point it is cutting.Moreover torch nozzle must satisfy the stringent requirement complicated by the fact that the cylindrical wall surface to be cut deviates appreciably from perfect roundness, that its distance from surf are is maintained at 1mm, the distance optimal for plasma cutting. The above-menhonal two requirements call for two effective measures to be taken. One measure is the design of an effective 4-coordinate trace device.The other measure is the introduction of decoupling technique so as to avoid causing y,z change from intended values when θis adjusted.μ computer control system incorporates certain available technical measures that are considered edvanced in China and also some new ideas of the authors.They all contribute to the performance of the machine in the three following respects:accumulative errors are avoided.the distribution of interpolation pulse is highly uniform, leading to increased cutting accuracy and the entire machine is more resistant to interference.After a careful world-wide search of flame cutting machine literature including patents,covering the 29yr period of 1963-1991 inclusive, by an agency appointed by the Chinese national patent ofice. the author received on July 15,1992 the Chinese Patent No.91124128.4.