Baldor MN1928 installation manual An introduction to closed loop control

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6.5.2 An introduction to closed loop control

This section describes the basic principles of closed loop control. If you are familiar with closed loop control go straight to section 6.6.1.

When there is a requirement to move an axis, the NextMove ES control software translates this into a demand output voltage. This is used to control the drive (servo amplifier) which powers the motor. An encoder or resolver on the motor is used to measure the motor’s position. Every 1ms* (adjustable using the LOOPTIME keyword) the NextMove ES compares the demanded and measured positions. It then calculates the demand needed to minimize the difference between them, known as the following error.

This system of constant measurement and correction is known as closed loop control.

[For the analogy, imagine you are in your car waiting at an intersection. You are going to go straight on when the lights change, just like the car standing next to you which is called Demand. You’re not going to race Demand though - your job as the controller (NextMove ES) is to stay exactly level with Demand, looking out of the window to measure your position ].

The main term that the NextMove ES uses to correct the error is called Proportional gain

(KPROP). A very simple proportional controller would simply multiply the amount of error by the Proportional gain and apply the result to the motor [ the further Demand gets ahead or behind you, the more you press or release the gas pedal ].

If the Proportional gain is set too high overshoot will occur, resulting in the motor vibrating back and forth around the desired position before it settles [ you press the gas pedal so hard you go right past Demand. To try and stay level you ease off the gas, but end up falling behind a little. You keep repeating this and after a few tries you end up level with Demand, travelling at a steady speed. This is what you wanted to do but it has taken you a long time ].

If the Proportional gain is increased still further, the system becomes unstable [ you keep pressing and then letting off the gas pedal so hard you never travel at a steady speed ].

To reduce the onset of instability, a term called Velocity Feedback gain (KVEL) is used. This resists rapid movement of the motor and allows the Proportional gain to be set higher before vibration starts. Another term called Derivative gain (KDERIV) can also be used to give a similar effect.

With Proportional gain and Velocity Feedback gain (or Derivative gain) it is possible for a motor to come to a stop with a small following error [ Demand stopped so you stopped too, but not quite level ]. The NextMove ES tries to correct the error, but because the error is so small the amount of torque demanded might not be enough to overcome friction.

This problem is overcome by using a term called Integral gain (KINT). This sums the error over time, so that the motor torque is gradually increased until the positional error is reduced to zero [ like a person gradually pushing harder and harder on your car until they’ve pushed it level with Demand].

However, if there is large load on the motor (it is supporting a heavy suspended weight for example), it is possible for the output to increase to 100% demand. This effect can be limited using the KINTLIMIT keyword which limits the effect of KINT to a given percentage of the demand output. Another keyword called KINTMODE can even turn off integral action when it’s not needed.

*The 1ms sampling interval can be changed using the LOOPTIME keyword to either 2ms, 500µs, 200µs or 100µs.

MN1928

Operation 6-13

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Contents NextMove ES Motion Controller Page Contents Backplanes Troubleshooting Appendices General Information Precautions Safety NoticeMN1928 Introduction NextMove ES featuresIntroduction MN1928 Identifying the catalog number InstalledReceiving and inspection Units and abbreviations PhaseLocation requirements You should read all the sections in Basic InstallationIntroduction Other requirements for installation Installing the NextMove ES card96-pin edge connector Row Pin 1 96-pin connector pin assignment96-pin connector pin assignment Analog inputs Analog I/OAIN0 analog input wiring Analog output Demand0 shown Analog outputsGeneral purpose inputs Digital I/ODigital inputs Auxiliary encoder inputs DIN17 STEP, DIN18 DIR, DIN19 Z Reset input !RSTINTypical digital input wiring DOUT0 DOUT7 Digital outputsDigital outputs DOUT8-11 DOUT8 shown DOUT8 DOUT11Error output Error Out Stepper control outputs Other I/OEncoder inputs Location Pin Name Description 96-pin Connector3 RS232 serial connection Pin Name Description USB connectionTypical can network connections Can connectionCANopen and Baldor can JP1 This will connect an internal terminating resistorDrive amplifier axis Connection summary minimum system wiringConnector details for minimum system wiring shown in Figure Backplanes BPL010-501 non-isolated backplane Analog outputs demands DIN1 Mating connector Weidmüller Omnimate BL 3.5/5 Digital output DOUT11 C22 Stepper axes outputs DIR3+ Pin Name Description 96-pin Power inputsEncoder input 13 RS232 serial communication BPL010-502/503 backplane with opto-isolator card Pin Name Description NextMove ES 96-pin Connector Relay connections Error relay connectionsAnalog output, DEMAND0 shown Customer power supply ground DIN15 USR V+ Digital input circuit DIN16 with ‘active low’ inputs 5.1 BPL010-502 Active high inputsUSR COM 6.1 BPL010-502 PNP outputs Digital output circuit DOUT8-11 DOUT8 shown Stepper axes outputs Pin Name Description 96-pin Connector Power inputs 13 RS232 serial communication Input / Output MN1928 \start Connecting the NextMove ES to the PCInstalling WorkBench Starting the NextMove ESPreliminary checks Power on checksInstalling the USB driver Help file WorkBenchStarting WorkBench MN1928 Operation Selecting a scale Configuring an axisSetting the drive enable output If you are going to use the error output, drag Testing the drive enable output Testing the output Stepper axis testingTesting the demand output Servo axis testing and tuningTORQUE.4=-5 An introduction to closed loop control Summary, the following rules can be used as a guide NextMove ES servo loop Selecting servo loop gains Servo axis tuning for current controlMN1928 Operation Underdamped response Underdamped responseOverdamped response Overdamped responseCritically damped ideal response Critically damped responseServo axis eliminating steady-state errors Calculating Kvelff Servo axis tuning for velocity controlKvelff Correct value of Kvelff Adjusting Kprop Correct value of Kprop Digital input configuration Digital input/output configurationDigital output configuration Saving setup information Loading saved information SupportMe feature Problem diagnosisStatus display NextMove ES indicatorsD3 yellow Surface mount LEDs D3, D4, D16 and D20Motor control Symptom CheckCommunication WorkBench Troubleshooting MN1928 Input power Maximum Minimum High Low Digital inputs non-isolatedDigital inputs opto-isolated Input voltageDigital outputs general purpose opto-isolated Digital output error output non-isolatedDigital outputs general purpose non-isolated Can interface Error relay opto-isolated backplanesEnvironmental Weights and dimensionsSpecifications MN1928 MN1928 Appendix A-1 Axis renumberingAppendix MN1928 Index Index MN1928 Underdamped response, 6-18 Units and abbreviations Index MN1928 Comment CommentsComments MN1928 Page Baldor Electric Company Box Ft. Smith, AR
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MN1928 specifications

The Baldor MN1928 is a highly regarded motor designed for a variety of industrial applications, known for its durability and efficiency. This motor is part of Baldor’s extensive range of products, which are engineered to meet the demands of heavy-duty operations.

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In summary, the Baldor MN1928 stands out as a reliable choice for industrial applications, offering a combination of durability, efficiency, and advanced technology. Its robust construction, high-efficiency design, and safety features make it a preferred option for many enterprises seeking dependable motor solutions.
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