Single machine processing , tool wear and breakage monitoring of workers with experience , and can still be normal production , while the FMS, CIMS, no factories, tool wear and breakage must address the problem of online real-time monitoring and control . Because the time to determine the extent of tool wear and breakage and online real-time control , is to improve the degree of automation of the production process and guarantee the quality of products, one of the key elements to avoid damage to the machine , tool , workpiece.
Block diagram of the monitoring methods to monitor wear and breakage monitoring tool to monitor the principle of the selection of parameters to monitor many principles can be divided into direct and indirect measurement method to measure two categories . Direct measurements are: optical method , the contact resistance method , radioactive method. Indirect measurement method are: the cutting force or power measurement , the tool and the workpiece measurement , temperature measurement , vibration analysis , AE method , the motor current or power measurement method .
Existing tool wear and breakage monitoring methods have advantages and disadvantages , we selected acoustic emission (AE) monitoring and motor current signal as a parameter . This is because the AE signal processing machine can avoid the worst effects of low-frequency noise , the suspension will affect the vibration and acoustic noise , high signal to noise ratio in the region of interest , ease of signal processing. Fast response, high sensitivity ; but heavy , susceptible to interference. Easy to extract the motor current signal , to accommodate all the machining process , there is no effect on the normal machining , but vulnerable to interference, slow response time , when the load is light , the sensitivity is low. Thus , while selected AE and motor current monitoring signal , you can use their strengths to monitor the amount of these two complementary and broaden the scope of monitoring , to improve monitoring accuracy and discrimination success rate.
Cutting process, when the tool wear and breakage occurs when the cutting force corresponding changes , changes in cutting force causes the motor output torque changes, which led to corresponding changes in the motor current , the current law is monitored by changes in electrical current, to achieve real-time to determine the indirect online tool wear and breakage . AE is a material or structure that is external or internal forces deformation or fracture in the form of elastic strain energy release waveform phenomenon . It has a low amplitude , the characteristics of a wide frequency range . Test and spectral analysis : AE signals generated mainly normal cutting plastic deformation of the workpiece material, the power spectrum distribution , 100kHz following values greatly , 100kHz or more small.
When the tool wear and breakage when , AE signal frequencies above 100kHz components when cutting larger than normal , especially frequency components between 100-300kHz bigger . To this end, band-pass filter , the frequency change monitoring component 100-300kHz AE signal , for monitoring tool wear and breakage .
Principle use of AE, the motor current signal integrated tool wear and breakage discriminant is: light load zone , relying AE envelope signal with the threshold method to discriminate ; in the load area , then the motor current and AE signals are functioning , using a combination of both methods discrimination and improve the success rate determination , the specific method is: if the AE AE signal exceeds the threshold, the delay constant is set ds ( value depends on the system configuration d ) , if the time in ds , the current signal is a current signal exceeds the threshold , the maximum tool wear or breakage judgment . If ds in time, the current value of the current signal, the signal threshold is not exceeded, no alarm, continued monitoring by the delay time constant . Such as the forerunner to AE , AE signals and motor current signals "and" discrimination mode , both the use of AE signals with real-time , sensitive characteristics, but also consider the nature of the motor current signal has lagged , with a strong anti-jamming ability to improve the success rate of discrimination . In a large load area , then the motor current signal -based , AE signal supplemented discriminate . The following figure shows a block diagram of the line monitoring system .
All the way to the middle of the grid voltage monitoring circuit , by monitoring fluctuations in the power supply , eliminating the effects of voltage fluctuations due to monitor and improve the anti-jamming capability . The dotted line is automatically subtracted from the first part of the current cut line , the first aim is to cut the current automatically reduced to the amount of current to determine the amount of changes to improve the sensitivity of the current signal monitoring .
