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Velocity Control with joystick


odoardo
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Good Morning

 

With a Power Brick AC, I want do motor velocity control with a joystick. The correct steps are:

 

1 Using a PLC, put the raw ADC data through a cubic function. The

ADC

data can be found in the high 16 bits of

PowerBrick[0].Chan[0].AdcAmp[2], for example.

 

2 Dump the result of the cubic into user buffer memory (e.g. in

Sys.Ddata[1]).

 

3 Create an encoder conversion table (ECT) entry to integrate the

result that's in user buffer.

 

4 Use the result of this ECT entry as the new master position of your

follower.

 

kindly, is possilbile to have a code example to perform this 4 steps?

 

thanks in advance

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This should get you started:

 

Declare:

 

ptr RawAdc->PowerBrick[0].Chan[0].AdcAmp[2]; // 32-bit register with ADC data in high 16 bits

ptr FiltAdc->Sys.Idata[2]; // 32-bit integer register in user shared memory buffer

 

open plc 0 // Real-time PLC executing under real-time interrupt

// Basic first order filter shown for simplicity

FiltAdc = 0.95 * FiltAdc + 0.05 * RawAdc / 65536; // Exponential low-pass filter on top 16 bits of input register

close

 

// Process filtered ADC data to prepare for motor

// Use 9th entry if first 8 entries auto-assigned

 

EncTable[9].type = 1; // Single-register integer read

EncTable[9].pEnc = Sys.Idata[2].a; // Address of source data

EncTable[9].index1 = 0; // No shift

EncTable[9].index2 = 0; // No shift

EncTable[9].index3 = 0; // No change limiting

EncTable[9].index4 = 1; // Integrate once

EncTable[9].EncBias = 0; // ? Possible offset before integration

EncTable[9].ScaleFactor = 1.0; // User-selectable output scaling

 

Motor[1].pMasterEnc = EncTable[9].a

Motor[1].MasterPosSf = 0.001; // User-selectable "gear ratio"; set low to start for safety

Motor[1].MasterCtrl = 1; // To enable following, set to 0 to disable

Motor[1].MasterMaxSpeed = ? // Possible speed clamp for safety

Motor[1].MasterMaxAccel = ? // Possible accel clamp for safety

 

**********************

You have indicated that you want to use a higher-order filter in your PLC program, which would be easy to do.

 

Many joystick users want to create a "deadband" around the 0 input voltage, so there is no drift when the joystick is in its rest position. This is also easy to do in the PLC program.

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A simple routine to provide "deadband" on the ADC from the joystick

 

global DbSize = 100; // Size of deadband in LSBs of 16-bit ADC

global DbAdc; // Modified reading

 

open plc 0

DbAdc = RawAdc >> 16; // Take top 16 bits of 32-bit register containing ADC

if (DbAdc > DbSize) DbAdc -= DbSize;

else if (DbAdc < - DbSize) DbAdc += DbSize;

else DbAdc = 0;

// Now filter modified ADC; simple 1st order filter example

FiltAdc = 0.95 * FiltAdc + 0.05 * DbAdc;

close

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