Baldor BXII installation manual An introduction to closed loop control

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5.5 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 5.6.1.

When there is a requirement to move an axis, the NextMove BXII 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 BXII 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 BXII) is to stay exactly level with Demand, looking out of the window to measure your position ].

The main term that the NextMove BXII 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 BXII tries to correct the error, but because the error is so small the amount of torque demanded might not be enough to overcome friction.

In this situation, a term called Integral gain (KINT) can be used. 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 remaining gain terms are Velocity Feed forward (KVELFF) and Acceleration Feed forward (KACCEL).

MN1904

Operation 5-11

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Contents NextMove Bxii Motion Controller Page Contents Operation Appendices Iv Contents MN1904 General Information Precautions Safety NoticeNextMove Bxii features Installed Receiving and inspectionIdentifying the catalog number Units and abbreviations PhaseIntroduction MN1904 Power sources IntroductionPC Hardware requirements Tools and miscellaneous hardware Other information needed for installationMechanical installation and location requirements Mounting the NextMove Bxii This completes the basic installationConnector locations top panel X8 Power Connector locations front panelPower Power connectionsAnalog inputs Analog I/OAnalog input circuit, AIN0/AIN1 pair shown Analog output circuit Demand0 shown Analog outputs DemandsDigital I/O Pin Name Mint keyword / description Digital inputsINX.0 Digital input circuit fast interrupts Digital inputs InterruptsDigital output circuit Digital outputsEncoder interfaces X9, X10, X11, X12 Other I/OEncoder input frequency Relay connections Relay and user power4 RS232 RS232 serial port connections Cable wiring if hardware handshaking is not required Connecting Baldor HMI Operator Panels6 RS422 / RS485 RS422 / RS485 connections on a 9-pin male D-type connectorWire RS485 multi-drop connections Typical can network connections Can connectors X16Baldor can CANopenSystem watchdog Reset statesServo amplifier axis Connection summary minimum system wiringMinimum system wiring connections Preliminary checks Connecting the NextMove Bxii to the PCInstalling the software Starting the NextMove BxiiPower on checks Help file WorkBenchStarting WorkBench MN1904 Operation Selecting a scale Configuring an axisSetting the drive enable output Testing the drive enable output Testing the drive command output Testing and tuningSTOP.0 An introduction to closed loop control Summary, the following rules can be used as a guide NextMove Bxii servo loop Selecting servo loop gains Tuning an axis for current controlMN1904 Operation Underdamped response Underdamped responseKprop Overdamped responseCritically damped ideal response Critically damped responseEliminating steady-state errors Calculating Kvelff Tuning an axis for velocity controlKvelff Correct value of Kvelff Click Go Adjusting KpropCorrect value of Kprop Digital input configuration Digital input/output configurationDigital output configuration Toolbox, click the Edit & Debug icon Saving setup informationLoading saved information SupportMet feature Problem diagnosisStatus display NextMove Bxii indicatorsMN1904 Troubleshooting Motor control Symptom CheckCommunication Axis LED is red or Status LED shows a flashing symbolTroubleshooting MN1904 Description Input powerDigital inputs X1 Relay output Encoder interfaces X9Can interfaces X16 10Environmental 11Weights and dimensionsBaldor can nodes Catalog number Description OPT008-501 Encoder Splitter/Buffer boardIndex Index MN1904 MN1904 Index Index MN1904 Comments Comments MN1904 Page LT0158A01

BXII specifications

The Baldor BXII is a robust and versatile industrial motor known for its high performance and reliability in various applications. Designed for use in demanding environments, the BXII series is particularly favored in the food processing, petrochemical, and material handling industries. Its construction and technological features distinctly differentiate it from other motors in the market, enhancing efficiency and durability.

One of the standout features of the Baldor BXII is its premium efficiency rating, which ensures that the motor operates with minimal energy loss. This efficiency is crucial for industries looking to reduce energy costs and lower environmental impact. The BXII motor meets or exceeds NEMA Premium Efficiency standards, making it an eco-friendly choice for operations requiring continuous power.

Another important characteristic of the BXII series is its advanced design, featuring a high-quality aluminum frame that promotes excellent heat dissipation. This construction enhances the lifespan of the motor and reduces the risk of overheating during extended operation. Additionally, the BXII is equipped with an IP55-rated enclosure, ensuring that it is well-protected against dust and moisture, which is vital for reliability in harsh environments.

The Baldor BXII incorporates state-of-the-art technology in its motor design, including an innovative rotor design that offers optimal torque characteristics. This carefully engineered rotor ensures smooth operation and minimal vibration, resulting in increased performance and reduced wear on mechanical components.

Moreover, the BXII series employs a continuous duty service factor, allowing for longer operational hours without overheating or compromising performance. This is particularly beneficial for applications requiring consistent power output over extended periods.

The integration of smart technologies in the BXII line also enhances its usability. Features such as thermal protection and vibration sensors enable proactive monitoring of motor health, leading to preemptive maintenance that reduces downtime and extends the life of the motor.

Overall, the Baldor BXII offers a winning combination of efficiency, durability, and advanced technology, making it a reliable choice for industrial applications. Its commitment to performance and innovation underscores Baldor's reputation as a leader in the manufacturing of high-quality motors, ensuring that businesses can operate with confidence and efficiency. Whether in a food processing facility or a manufacturing plant, the BXII series stands out as an exemplary choice for those seeking dependable motor solutions.
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