Patent ID: 6840104

Claim:
A crankshaft rotational balance testing apparatus comprising: crankshaft rotation means for rotating a crankshaft to be tested about a central axis of the crankshaft; sensor means for detecting positional variations of the central axis of a tested crankshaft being rotated and producing an analog vibration signal representative of the detected positional variations of the central axis of the tested crankshaft; a memory that stores digital reference dummy data comprising equivalent dummy amounts indicative of predetermined amounts of unbalance to be left in respective crankpins of each tested crankshaft, the digital reference dummy data being determined in advance using a balance-adiusted reference crankshaft having crankpins with no rotational phase error and with dummy weights attached thereto; phase error determination means for determining errors in rotational phase of respective crankpins of the tested crankshaft while the tested crankshaft is being rotated about its central axis; dummy information generation means for creating digital dummy data representative of rotational unbalance components to be removed from detected positional variations of the central axis of the tested crankshaft, by retrieving the digital reference dummy data from the memory and modifying the retrieved digital reference dummy data according to the rotational phase errors of the respective crankpins of the tested crankshaft determined by the phase error determination means, such that the equivalent dummy amounts thereafter produce rotational unbalance components oscillating in phase with the respective crankpins of the tested crankshaft; a digital-to-analog converter for converting the digital dummy data into an analog dummy signal; a waveform synthesizing circuit for performing subtractive synthesis of the analog vibration signal and the analog dummy signal to thereby produce an analog initial unbalance signal indicative of an amount and an angle of initial unbalance of the tested crankshaft; and an analog-to-digital converter for converting the analog initial unbalance signal to a digital initial unbalance signal.