Mechatronics | PartQuest™ Explore

Copy of LVDT Position Sensing System - on Wed, 01/13/2021 - 10:55

Designer237530

Member for

4 years 3 months

0

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

A Linear Variable Differential Transformer (LVDT) and analog signal conditioning circuit are used for a position sensing system. An oscillator provides a sinusoidal excitation signal to the primary winding of the LVDT. The differential secondary winding outputs are rectified and low-pass filtered. The difference voltage, which is proportional to the mechanical displacement of the LVDT core, is the measurement result.

This virtual prototype can be used to select the low pass filter frequency, so it is low enough that the oscillation frequency is mostly removed from the output signal, yet high enough to track the natural frequency of mechanical system the sensor is intended to measure. It can also be used to analyze parasitic effects, such as the resistance of the wires connecting the sensor to the signal conditioning circuits. This resistance affects the output voltage and therefore corrupts the measurement results. Likewise, the non-linear behavior of the rectifier diodes affects the linearity of the position measurement.This can be seen if the force input is slowly ramped from -1000N to 1000N over a 1 second interval.

About text formats

Copy of ServoDC_PID_continuo - on Mon, 01/04/2021 - 17:15

Description

A Linear Variable Differential Transformer (LVDT) and analog signal conditioning circuit are used for a position sensing system. An oscillator provides a sinusoidal excitation signal to the primary winding of the LVDT. The differential secondary winding outputs are rectified and low-pass filtered. The difference voltage, which is proportional to the mechanical displacement of the LVDT core, is the measurement result.

This virtual prototype can be used to select the low pass filter frequency, so it is low enough that the oscillation frequency is mostly removed from the output signal, yet high enough to track the natural frequency of mechanical system the sensor is intended to measure. It can also be used to analyze parasitic effects, such as the resistance of the wires connecting the sensor to the signal conditioning circuits. This resistance affects the output voltage and therefore corrupts the measurement results. Likewise, the non-linear behavior of the rectifier diodes affects the linearity of the position measurement.This can be seen if the force input is slowly ramped from -1000N to 1000N over a 1 second interval.

About text formats

Copy of Loudspeaker with Simple Amplifier - on Mon, 12/07/2020 - 22:53

Designer237048

Member for

4 years 4 months

0

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

This "Live" example design includes a simple analog electronic amplifier, intended only to demonstrates the importance of multi-discipline system modeling.

A swept frequency response test, from 40 Hz to 1000 Hz, shows the effect of the complex amplifier loading by the voice-coil and speaker-cone dynamics*. The electro-mechanical resonances strongly affect the current that must be supplied, in order to maintain a flat (controlled) output voltage over the specified frequency range. For example, the current in the voice-coil reaches a null at time 0.1 seconds, which corresponds to the effective "spring-mass" resonance frequency (60 Hz). The loudspeaker reaches its minimum impedance around 600 Hz, or at 0.6 seconds where the peak load current is observed.

The simulation results also show that the average power (q1/npn/pwr_avg) in the BDP947 BJT exceeds its 5 Watt rating across the entire range, but especially at lower frequencies. The red "hot part monitor", with the junction to ambient thermal resistance set to 10 C/Watt, as given in the datasheet, shows the part temperature rising to over 100 C. These diagnostic indicators make it obvious that we need a bigger transistor!

All of the parameters in blue can be changed by the user and a new simulation run. The updated scope waveform results will show the effect of that change. You can change the electrical resistance and inductance of the voice-coil, as well as the speaker cone mass and linear spring rate that affect the resonance frequency.

* Note: Please refer to this companion example, that shows the input impedance frequency response of the loudspeaker alone:

https://www.systemvision.com/design/loudspeaker-only-frequency-response

About text formats

Copy of Loudspeaker with Simple Amplifier - on Mon, 12/07/2020 - 22:53

Designer237048

Member for

4 years 4 months

0

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

This "Live" example design includes a simple analog electronic amplifier, intended only to demonstrates the importance of multi-discipline system modeling.

A swept frequency response test, from 40 Hz to 1000 Hz, shows the effect of the complex amplifier loading by the voice-coil and speaker-cone dynamics*. The electro-mechanical resonances strongly affect the current that must be supplied, in order to maintain a flat (controlled) output voltage over the specified frequency range. For example, the current in the voice-coil reaches a null at time 0.1 seconds, which corresponds to the effective "spring-mass" resonance frequency (60 Hz). The loudspeaker reaches its minimum impedance around 600 Hz, or at 0.6 seconds where the peak load current is observed.

The simulation results also show that the average power (q1/npn/pwr_avg) in the BDP947 BJT exceeds its 5 Watt rating across the entire range, but especially at lower frequencies. The red "hot part monitor", with the junction to ambient thermal resistance set to 10 C/Watt, as given in the datasheet, shows the part temperature rising to over 100 C. These diagnostic indicators make it obvious that we need a bigger transistor!

All of the parameters in blue can be changed by the user and a new simulation run. The updated scope waveform results will show the effect of that change. You can change the electrical resistance and inductance of the voice-coil, as well as the speaker cone mass and linear spring rate that affect the resonance frequency.

* Note: Please refer to this companion example, that shows the input impedance frequency response of the loudspeaker alone:

https://www.systemvision.com/design/loudspeaker-only-frequency-response

About text formats

Copy of PID Speed Control Loop - Continuous - on Mon, 12/07/2020 - 06:22

Designer237035

Member for

4 years 4 months

1

designs

1

groups

Add a bio to your profile to share information about yourself with other SystemVision users.

Description

This example shows a motor speed control loop that uses a PID control strategy (Proportional, Integral and Derivative), with continuous function blocks representing the controller up to the ideal voltage motor drive.

The parameter values of the generic DC motor model were calibrated to represent an FRC - First Robotics Competition CIM Motor, as described in the article “<a href="https://www.systemvision.com/blog/first-robotics-frc-motor-modeling-may-6-2016">First Robotics (FRC) Motor Modeling</a>”. The voltage drive, the motor and the mechanical fan load were “assembled” using a conservation-based modeling approach. This approach to system modeling is much like assembling a hardware prototype, and does not require the user to develop an analytical model of the “plant” being controlled. Both the static and dynamic system characteristics “emerge” naturally from the model, simply because they are connected on the schematic. Additional electrical circuit components, mechanical loads and other “physical” elements can easily be added by simply placing them on the schematic and “wiring” them together. In fact, a more detailed implementation of the motor drive is shown in the companion example, “<a href="https://www.systemvision.com/groups/mikedonnellys-workspace/designs/pid-speed-control-loop-switching">PID Speed Control Loop – Switching</a>”. In that example, a design for the logic and power electronics needed to implement a PWM-based, switched MOSFET H-bridge drive is included.

Because this version simulates very quickly compared to the switching version, it is well suited for early validation of the control strategy and PID tuning, as well as loop stability and frequency response analysis. Note that the P, I and D "gains" for this nominal design were computed using the <a href="https://en.wikipedia.org/wiki/Ziegler%E2%80%93Nichols_method">Ziegler-Nichols</a> classic PID tuning method.

Another version of this design, which simulates quickly but includes the important and practical aspect of a limited drive voltage range, is show in “<a href="https://www.systemvision.com/groups/mikedonnellys-workspace/designs/pid-speed-control-loop-continuous-and-limited">PID Speed Control Loop – Continuous and Limited</a>”. It is instructive to compare the speed step response between that design and this one.

About text formats

Terms of Use Cookie Notice Data Privacy Notice