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A machine operation monitor is provided for detecting malfunctions during execution of a machine cycle of operation irrespective of the activity being performed. Load levels of machine member driving means are periodically sampled and compared against limits computed by the monitor. The limit calcul

A machine operation monitor is provided for detecting malfunctions during execution of a machine cycle of operation irrespective of the activity being performed. Load levels of machine member driving means are periodically sampled and compared against limits computed by the monitor. The limit calculation uses net force or torque measured by storing load level samples during two preparatory executions of the machine cycle of operation. During the first execution a finished workpiece is produced using good tools. During the second execution no workpiece is present. The differences between load level samples taken during these two executions represent the net force required to perform work on the workpiece. The monitor responds to synchronization signals to maintain correspondence between load level samples taken in successive executions of the machine cycle. The monitor also responds to monitor off signals to suspend monitor operation during periods of no activity in the machine cycle.

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1. Apparatus for detecting a malfunction during an execution of a machine cycle of operation, the machine having at least one movable member driven by driving means for effecting relative motion between a workpiece and a tool, the apparatus comprising: (a) means for periodically producing load le

1. Apparatus for detecting a malfunction during an execution of a machine cycle of operation, the machine having at least one movable member driven by driving means for effecting relative motion between a workpiece and a tool, the apparatus comprising: (a) means for periodically producing load level signals during an execution of the machine cycle of operation, each load level signal representing a driving means load level; (b) means for storing signature load level signals produced during a first execution of the machine cycle of operation when a workpiece is present; (c) means for storing base load level signals produced during a second execution of the machine cycle of operation when a workpiece is not present; (d) means responsive to the signature load level signals and the base load level signals for producing limit signals, each limit signal representing a load level defining an acceptable maximum driving means load for a predetermined interval occuring during an execution of the machine cycle of operation; (e) means for comparing load level signals produced during subsequent executions of the machine cycle of operation to the limit signals; and (f) means responsive to the comparing means for producing an error output signal when a load level signal exceeds a limit signal. 2. The apparatus of claim 1 wherein the machine has a plurality of movable members and driving means and the means for producing load level signals further comprises: (a) means for sampling the load level of each driving means; and (b) means responsive to the sampling means for producing channel load level signals representing the periodic load level of each driving means. 3. The apparatus of claim 2 wherein the limit signal producing means produces limit signals for each driving means. 4. The apparatus of claim 2 wherein one of the machine movable members is a spindle and the load level producing means further comprises means for producing a torque level signal. 5. The apparatus of claim 1 wherein the limit signal producing means further comprises: (a) means for computing difference signals representing the load level difference between the base and signature load levels; and (b) means responsive to the difference signals for producing the limit signals. 6. Apparatus for detecting a malfunction during an execution of a machine cycle of operation, the machine having at least one movable member driven by driving means for effecting relative motion between a workpiece and a tool, the cycle of operation being executed in response to a program including synchronization codes for producing synchronization signals, the apparatus comprising: (a) interval counting means for producing periodic interval signals representing times at which driving means load level samples are to be taken during an execution of the machine cycle of operation; (b) means responsive to the periodic interval signals for periodically producing load level signals, each load level signal representing a driving means load level occurring at a time defined by a periodic interval signal; (c) means for storing signature load level signals produced during a first execution of the machine cycle of operation when a workpiece is present; (d) means for storing base load level signals produced during a second execution of the machine cycle of operation when a workpiece is not present; (e) means responsive to the signature load level signals and the base load level signals for producing limit signals, each limit signal representing a load level defining an acceptable maximum load for a predetermined interval occurring during an execution of the machine cycle of operations; (f) means for comparing load level signals produced during subsequent executions of the machine cycle of operation to the limit signals; and (g) means responsive to the comparing means for producing an error output signal when a load level signal exceeds a limit signal. 7. The apparatus of claim 6 wherein the limit signal producing means further comprises: (a) means for computing difference signals representing the load level difference between the base and signature load levels; and (b) means responsive to the difference signals for producing the limit signals. 8. The apparatus of claim 7 further comprising: (a) means responsive to the counting means and the synchronization signals for producing synchronization time signals during the first execution of the machine cycle; (b) means for storing the synchronization time signals; and (c) means responsive to the stored synchronization time signals and the synchronization signals for setting the value of the periodic interval signal during the subsequent executions of the machine cycle. 9. The apparatus of claim 7 wherein the means for storing base load signals stores a base load signal representing a minimum value occurring during the predetermined interval and the means for storing the signature load signals stores a signature load signal representing a maximum value occurring during the predetermined interval. 10. Apparatus for detecting a malfunction during an execution of a machine cycle of operation, the machine having at least one movable member driven by driving means for effecting relative motion between a workpiece and a tool, the cycle of operation being controlled by a machine control executing a program including monitor inhibit command codes, the control outputting monitor off signals in response to the monitor inhibit commands, the apparatus comprising: (a) interval counting means responsive to a monitor off signal for producing periodic interval signals representing times at which driving means load level samples are to be taken during an execution of the machine cycle of operation; (b) means responsive to the periodic interval signals for periodically producing load level signals each load level signal representing a driving means load level occurring at the time defined by the interval signal; (c) means for storing signature load level signals produced during a first execution of the machine cycle of operation when a workpiece is present; (d) means for storing base load level signals produced during a second execution of the machine cycle of operation when a workpiece is not present; (e) means responsive to the signature load level signals and the base load level signals for producing limit signals, each limit signal representing a load level defining an acceptable maximum driving means load for a predetermined interval occurring during an execution of the machine cycle of operation; (f) means for comparing load level signals produced during subsequent executions of the machine cycle of operation to the limit signals; and (g) means responsive to the comparing means for producing an error output signal when a load level signal exceeds a limit signal.