Method of detecting execution errors in program-controlled apparatus

In the combination of a programmable controller (1) and a device (M), particularly a machine tool, controlled thereby, in which:

• said controlled device (M) includes operating elements (V) selectively controlled by the programmable controller, and transducers (T) and control lines connected to, and signaling operating conditions of, the device (M) to the programmable controller (1);
• said programmable controller (1) issues commands to said operating elements, based upon a set of program instructions stored at memory locations or addresses within said controller;
• said program comprises a sequence of program steps, each of which can be initiated only upon occurrence of a RESET status at the end of any preceding step;
• certain of said program instructions comprise SET commands and certain of said program instructions comprise AND commands;
• a diagnostic unit (2), including a random-access memory (RAM), is connected to the programmable controller (1);
• and
• a malfunction output indicator (6, 49) is provided, controlled by the diagnostic unit and indicating malfunction, and the nature of the malfunction, in the run of a program in which the programmable controller (1) controls sequential operating steps or conditions of said controlled device,
• a method of recognizing errors in the execution of the program steps, and hence of the control signals applied by the programmable controller (1) to the controlled device (M),
• comprising the steps of
• loading sequentially into said diagnostic unit (2) consecutive instructions of the stored program within the programmable controller (1)
• analyzing each instruction to determine whether it contains a SET command and, if so, storing the instruction in the RAM of the diagnostic unit;
• loading sequentially into said diagnostic unit (2) the instruction, of the stored program within the programmable controller (1), adjacent to and preceding each SET-command-containing instruction;
• analyzing said preceding instruction to determine whether it contains an AND operator and, if not, erasing said adjacent SET-command-containing instruction from the RAM of the diagnostic unit as not being indicative of a program step;
• upon the lapse of more than a predetermined period of time for execution of a predetermined portion of the program, searching for the last program step which terminated in a RESET status, then determining which of several necessary conditions for the completion of the next succeeding step was not satisfied;
• and, providing an output indication on the malfunction output indicator (6, 49) indicating the source of each signal which did not satisfy the necessary condition for completion of the next succeeding step.