High performance CNC machine communication circuit composition and algorithm of spindle drive system

Numerical control machine tool requires drive system, speed, wide speed range and high precision, fast response speed, deceleration performance is good, strong protection function etc.High performance CNC machine ac spindle drive system based on intelligent power module IPM inverter switch components, mainly MCS96 series double single chip microcomputer controller, control algorithm adopts digital slip frequency vector control.Main controller adopts double CPU structure, a CPU speed loop control, monitoring and display, etc.;Another slice of the CPU to control the motor speed, 80 c196mc complete current inner loop control.By sharing RAM to communicate between two pieces of CPU, effectively solves the problems of general CPU capacity is not strong.Composed of intelligent power module IPM is used in the main circuit voltage ac\/rectangular inverter.The system also has a fully functional detection and protection circuit, etc.Experiments show that the system has good static and dynamic performance, and can meet the above requirement of driving system of nc machine tools.1, the main loop of the main circuit USES a rectangular voltage type structure, mainly by the rectifier circuit, filter and inverter circuit, etc.Inverter circuit adopts new power devices & ndash;Intelligent Power Module (Intelligent Power Module, IPM).Intelligent power module IPM is an advanced hybrid integrated intelligent power module, it is composed of high speed, low consumption of IGBT chip and optimize the gate drive and over current, short circuit, undervoltage and overheat protection circuit, after IGBT is another innovative achievements in the field of power electronic technology.Because internal IPM adopted for monitoring the current of IGBT chip devices, realize the efficient over-current protection and short circuit protection;IPM has integrated the internal overheating and under-voltage protection circuit, greatly improving the system reliability;IPM has integrated the internal insulated gate bipolar transistor IGBT and its driver circuit, shorten the product development cycle;Loss of IPM on state and switching loss is low, reduce the heat sink size, reduce the cost.So, compared with IGBT intelligent power module IPM has obvious advantages.2, the control circuit in order to realize the fast real-time and reliable control of nc machine tool, control circuit used 80 c196mc – 80 c196kc double single-chip microcomputer 80 c196mc CPU structure has high computing speed and strong control ability, its task is to complete the current inner loop control of high real-time requirements, generating PWM control signal, complete protection function.Especially 80 c196mc contains three phase waveform Generator WFG (Wave Form Generator).WFG has three synchronous PWM module, each module contains a phase comparison register, a no signal time (dead – time) generator and a pair of programmable output.WFG can produce independent three pairs of PWM waveform, they have a common carrier frequency, no signal time and the operating mode, once started, WFG requires only the CPU in the PWM duty cycle is changed to intervene.If use 16 MHZ crystals, center on the cycle of PWM carrier for 0.15 & mu;S ~ 16 ms, increment of 0.25 & mu;S, no signal time adjusting range of 0.125 ~ 125 & mu;S.Used to keep a pair of complementary PWM signal time effectively at the same time, to ensure the output waveform is not overlapping.WFG greatly simplifies the synchronous pulse width modulation (PWM) used to generate the waveform control software and hardware peripherals, especially suitable for the control of three phase ac induction motor, brushless dc motor can also be used to control and other require multiple PWM output device.Unique feature of WFG80C196MC\/MD.80 c196kc mainly complete the speed control and test, the keyboard interrupt input and modify the important parameters, display information about the vector transformation, offering 80 c196mc command signal, etc.Double microcomputer communication between the Shared RAM method, in order to improve the running speed of the system.80 c196kc will calculate the current loop of the required parameters, such as the excitation current and torque current, rotating angular velocity, etc., and transfer to the Shared RAM corresponding unit, while 80 c196mc is to read the data from the Shared RAM.3, 1) detection and protection circuit, current detection because of nc machine tools for wide speed range, as a result, the frequency of the output current range is larger, the average current transformer can not meet the requirements, the hall current transformer is adopted to test the output current.Hall current transformer is characterized by small volume, fast response speed, high accuracy and linearity.2) speed sampling due to the numerical control machine, high speed control precision required average velocity components is difficult to meet the requirements, therefore adopt 1024 high resolution of the photoelectric pulse encoder, in order to realize the high-speed positioning, high-speed tapping, profile control, etc.3) protection function of intelligent power module IPM has good performance of the built-in protection circuit, in order to avoid the stress and make the system failure or damage of power devices.A protection circuit action, if the IPM module IGBT gate drive unit will shut off drive pulse, and the output of a fault signal.Internal protection function has the following several kinds of IPM module.1) the supply voltage locking (UV) IPM internal control circuit consists of 15 v dc power supply, if for some reason the under-voltage action value of the power supply voltage is lower than (UV), the power will be shut off device and outputs a fault signal;Only when the supply voltage than under voltage reset value (UVr) circuit to resume normal work.If the disturbance signal duration is less than the prescribed tDUV, under-voltage protection circuit will be ignored, the normal work of the control circuit, so that we can effectively avoid the interference signal’s influence on the normal work of the circuit.Between UV and UVr should have certain difference, so that you can avoid frequent switching under-voltage protection circuit, ensure the normal operation of the circuit.2) overheating protection (OT) inside the IPM is equipped with temperature sensors, used to detect the working temperature of power device.If the sensors detect the substrate temperature exceeds the overheating action value (OT), IPM internal control circuit as the bridge arm device gate driver, the control input signal is invalid, and the fault signal bridge arm, until the temperature returned to normal, so as to protect the power component.When the temperature dropped below to overheating reset value (OTr), and the control input is high level (off), the power device will accept under a low level (open) the input signal and resume normal work.Also, to avoid overheating protection actions frequently, in overheating action value OT and overheat reset between OTr also has difference of 20 ℃.3) over-current protection (OC) IPM IGBT, with current sensor used to measure the working current of power devices, the current through the IGBT if beyond a time to value (OC), flow is greater than the toff (OC), IGBT will be shut off.But time is more than OC number less than toff (OC) of current pulse, over-current protection circuit will be ignored.When detecting produced current, IPM internal control the IGBT soft circuit is cut off, a breakdown at the same time the output signal.Soft shut off can control shut off when large current generated by the surge voltage, so as to avoid the surge voltage is too high, effectively guarantee the safety of IPM.4) short circuit protection (SC), if the load short circuit or system controller failure resulting in upper and lower bridge arm conduction directly, IGBT make the current more than short circuit protection action value (SC), IPM built-in short-circuit protection circuit will start the soft shut off, shut off the IGBT, and the output of a fault signal.Due to the third generation IPM used the real-time current control circuit (RTC), it is directly monitoring level at the end of the IGBT driver circuit current, between SC detection and shut off the response time of the reduced to less than 0.1 & mu;S, which greatly reduced the short circuit current amplitude stress and peak voltage, power, effectively guarantee the safety of IPM.In order to guarantee the system running safely and reliably, in addition to IPM since the protection function, the system will also include a over-current, short circuit, ac\/dc overvoltage, undervoltage, short of all protection measures and the protection of fuse.4, control algorithm for numerical control machine and high precision requirements, the control algorithm USES the slip frequency vector control.Is to put the ac motor vector control simulation to control dc motor, ac motor stator current vector through coordinate transformation are divided into the two according to the rotor field-oriented dc component, and carries on the control of the two components, can achieve the same as the dc motor speed control performance.In the slip frequency vector control algorithm, used to motor parameters, if do not tally with the actual values given parameter, torque and rotor flux value is not equal to their instructions.Here the error of the rotor time constant is important, it directly affect the dynamic and static characteristics of vector control, so need to make proper compensations to the rotor time constant.Under the load of a certain situation, motor running in the best state, is considered to achieve the field-oriented control.Methods is to select motor error between the actual rotating angular velocity and angular velocity given absolute value as the target function, for the optimization of the rotor time constant.That when current and stable operation, select the appropriate rotor time constant to make the error minimum absolute value.Set speed ring once every 1 ms sampling, and put each 163 sampling points as a set of data, this 163 times the sampling time is about 4 s.Each time constant after optimization, let the motor run 4 s, and then continue sampling optimization.Due to the limitation of length, & other;The ac motor vector transformation control principle & throughout;Go here, please see the relevant references.5, summarize the system adopted the structure of the double CPU control circuit, a CPU to control the speed loop, another slice of CPU is used in the current inner loop control;Inverter circuit adopts intelligent power module;Control algorithm USES the slip frequency vector control, excitation current and torque current control independently.In the experiment choose nc machine tools with ac spindle frequency conversion motor, 11 kw power rating, speed 1500 r\/min.The experimental results show that the motor running smooth, good characteristics at low speed, stator current is close to sine wave, this system very well meet the requirements of the nc machine tools to drive system.