Impact Printer System Design Based On Cortex-M4 CPU And CPLD Technology

Impact printer is different from laser,inkjet,or thermal printers.It is rely on mechanical force to hit the ribbon to display information.This unique feature makes it possible to print multiple layers of press-sensing papers.Meanwhile,the Impact printer has specific paper fitting channel which make it possible to print various types of cards and docs.Therefore,impact printers are large-scale used in the postal,logistics,taxation and other fields.This paper developed a new impact printer design solution based on Cortex-M4 CPU and CPLD technology.For different pin arrangement types of print-head,CPU set control information to CPLD.So it is easily to drive print-head by CPLD without changing hardware circuit.Adopting NMOS to drive the coil in the print-head and remove the inductive load's discharge circuitry.Using chopper driving circuitry control the current flowing through the NMOS when it steps into avalanche state.By controlling the current in a reasonable amount,the energy stored in the coil is discharged by the NMOS safely.The chopper circuitry's driving cycle and duty-cycle are set by CPLD.This solution has resulted in significant cost savings.The stepper drive signal monitoring function is also designed inside CPLD,it will generate an alarm signal when the drive signal times out notifying the CPU to turn off the drive signal and protect the driving circuit.The system adopts the low power design idea,and shut down the power of the inactive circuit modules when the system steps into hibernation mode.Regarding to the paper sensing module,a correction algorithm is invented to adapt to the discreteness of the flat reflective photoelectric sensors.It can simultaneously monitor multiple sensor signals and carry out the paper correction function.The system ground is divided into power ground and signal ground.The print-head drive circuit and stepper drive circuit are placed in the power ground area.Digital circuit and analog circuit are placed in the signal ground area.Finally the two parts are grounding at the power supply's ground terminal.Regarding to the high frequency signal and high sensitive signal such as clock and analog signal,these signals are routed accompanying with ground trace.Meantime,using TVS diode avoid ESD interference.EMC test report showed us a pretty good result.In the course of the research,one invention patent and four utility model patents were published.The invention patent is: A printer paper correction system and correction algorithm.The four utility model patents are: A low-power circuitry for impact printer;Design of printer circuit based on CPLD implementation;A multichannel inductive loads drive and control circuitry;Impact printer print-head drive circuit based on MOSFET and TVS technology.