Arrangement for monitoring the quality of electric welds

Apparatus for monitoring the quality of welds on can bodies, each body having a weld seam extending along the length of the can body and being composed of a plurality of individual welds, said apparatus comprising:

• means for measuring a welding parameter value associated with the formation of each weld in a weld seam extending along the length of a can body and establishing a welding parameter profile composed of the measured values along the weld seam;
• memory means for storing as welding parameter profiles the values of the welding parameter from a plurality of weld seams determined to be good weld seams;
• means for statistically evaluating the stored values of the welding parameter profiles of the good weld seams and determining an average welding parameter profile (F.sub.m);
• means for also storing in the storing means the average welding parameter profile (F.sub.m) as the first welding parameter profile;
• means for statistically evaluating the stored values of the welding parameter profiles of the good welding seams and determining a reject limiting-value band (F.sub.g.+-.) enveloping the average welding parameter profile (F.sub.m) from the mean values of the stored welding parameter values used to determine the first welding parameter profile and from the product of a standard deviation of these welding parameter profiles assumed to be normally distributed and at least one sensitivity factor;
• and
• comparator means for establishing that a second welding parameter profile measured along the weld seam of another can body by the means for measuring lies within the reject limiting-value band (F.sub.g.+-.).

An apparatus for monitoring the quality of electric welds on can bodies, each can body having a weld seam formed by a plurality of welds extending continuously along the length of a can body, each weld being associated with a welding parameter of a given value, said apparatus comprising:

• means for receiving weld signals indicative of the value of the welding parameter as measured for each weld, with a set of said parameter values for each weld seam;
• at least one means for determining from said weld signals an average welding parameter profile (Fm) computed from a group of acceptable weld seam parameter value sets measured on a plurality of acceptable welded can bodies;
• store means to store the average welding parameter profile;
• a comparator to compare the average welding parameter profile with welding parameter profiles measure later on subsequently welded can bodies for determining a degree of agreement between the average welding parameter profile and each of said subsequently welded can body welding parameter profiles;
• evaluation means for providing statistical evaluation of said subsequently welded can body welding parameter profiles and determining a reject limiting-value band (Fg.+-.) enveloping the average welding parameter profile (F.sub.m) from computed mean welding parameter values for each weld in said group of acceptable weld seam parameter value sets and from the product of a standard deviation of said welding parameter values for each weld in said group of acceptable weld seam parameter value sets assumed to be normally distributed and at least one weld quality sensitivity factor;
• the comparator further generating output signals indicative of whether each welding parameter value of said subsequently welded can body welding parameter profiles lies within the reject limiting-value band (Fg.+-.);
• and
• signal processing means including a can body ejector connected with the comparator and responsive to the output signals for ejecting a can body if the measured welding parameter profile for the body does not lie within the reject limiting-value band (F.sub.g .+-.).

An apparatus for monitoring the quality of electric welds on can bodies, each can body having a weld seam formed by a plurality of welds extending continuously along the length of a can body each weld being associated with a welding parameter of a given value, said apparatus comprising:

• means for receiving weld signals indicative of the value of the welding parameter as measured for each weld, with a set of said parameter values for each weld seam;
• at least one means for determining from said weld signals an average welding parameter profile (Fm) computed from a group of acceptable weld seam parameter value sets measured on a plurality of acceptable welded can bodies;
• store means to store the average welding parameter profile;
• a comparator to compare the average welding parameter profile with welding parameter profiles measured later on subsequently welded can bodies for determined a degree of agreement between the average welding parameter profile and each of said subsequently welded can body welding parameter profiles;
• evaluation means for providing statistical evaluation of said subsequently welded can body welding parameter profiles and determining a reject limiting-value band (Fg.+-.) enveloping the average welding parameter profile (F.sub.m) from computed mean welding parameter values for each weld in said group of acceptable weld seam parameter value sets and from the product of a standard deviation of said welding parameter values for each weld in said group of acceptable weld seam parameter value sets assumed to be normally distributed and at least one weld quality sensitivity factor;
• the comparator further generating output signals indicative of whether each welding parameter value of said subsequently welded can body welding parameter profiles lies within the reject limiting-value band (Fg.+-.);
• and
• a controller responsive to the comparator output signals and generating signals to adjust said welding parameter value to bring said subsequently welded can body welding parameter values within the reject limiting-value band (Fg.+-.).