Automatic Velocity Control in Cutting-off Machines Carlos Machado 1 , Jaime Fonseca 2 and José Mendes 3 University of Minho 1,2,3 Dept. of Industrial Electronics Campus de Azurem, Portugal Phone: +351253510190, Fax:+351253510189 e-mail:{carlos.machado | jaime.fonseca | jose.mendes }@dei.uminho.pt 3 Addressee for correspondence Abstract– Usually, automatic cutting-off machines, of metallic pipes or bars, use constant cutting velocity. This mode of operation, constant cutting velocity combined with different profiles of materials to be cut, causes variable cutting forces to be applied to the saw. As a result, the cutting off machine is generally set for the worst expected conditions, otherwise excessive wear of the saw and machine will occur. Further, traditional cutting-off machines require adjustments to be made in order to automatically detect the completion of a cut. The objective of this project is the study of the application of control algorithms to the process of cutting-off metallic pipes or bars, with variable profiles, implemented in an industrial cutting-off machine, commercially available. The testes algorithms concern real-time cutting control and automatic detection of cut completion. The algorithms are implemented in a low cost Programmable Logic Controller (PLC), allowing its adoption in industrial applications without significant increase on machine cost. All algorithms were developed having in mind safety issues relative to the operation of the cutting machine in order to prevent damage to the machine itself.. Also, all process related relevant parameters are monitored on a Personal Computer using OPC (Object Linking and Embedding – for Process Control). Index Terms— Automatic velocity control cutting-off 1 Introduction Usually, automatic cutting-off machines, adopt a constant cutting velocity mode. This mode of operation, constant cutting velocity combined with different profiles of materials to be cut, causes variable cutting forces to be applied to the saw. As a result, the cutting off machine is normally set for the worst expected conditions, otherwise excessive wear of the saw and machine will occur. On one hand, if the cutting velocity is too high the worn of the saw as well as the components of the machine are too high. On the other hand, if the cutting velocity is too slow the cutting time significantly increases, reducing productivity of the automatic cutting machine. Further, traditional cutting-off machines require the adjustment of the position of a limit switch in order to automatically detect when the cut of a piece has been completed. In this project, different control algorithms were developed and applied in order to optimize the cutting process by diminishing cutting times and maximizing life time of the saw and machine components. Also, a new method for automatic detection of the completion of the cutting of a piece was developed, therefore neither a limit switch nor its adjustment is any longer necessary [1]. Fig. 1: Pipe Cutting. Fig. 2: Rod Cutting. 2 Description In Figure 1 and Figure 2, respectively, the profile of a tube and a rod are shown. If materials with such profiles are to be cut, the exact amount of material that has to be removed at a specific point is also shown, assuming that cutting is performed by a linear saw. The amount of material to be removed is closely linked to the required torque to be applied on the saw. The cutting torque requirements depend on the profile of the pipe, rod or bar, as shown in Figures 1 and 2. Cutti ng Mater i al -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 -4 0 4 8 12 16 20 24 28 32 36 40 44 Rod Profile Cutting Direction Cutti ng Mater i al -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24 -4 0 4 8 12 16 20 24 28 32 36 40 44 Pipe Profile Cutting Direction 0-7803-7852-0/03/$17.00 ©2003 IEEE ICIT 2003 - Maribor, Slovenia 1046