Current limit output to DC motor
Hello,
I am a student and I have to install a simple motion system (1 axis) for my current project.
Before I start programming I would like to limit the current output to the DC motor from the drive to <1 amps to avoid any fast motion.
It there a way to set a limit through LabVIEW and the motion controller? Or do I have to find a hardware limit on the drive?
The system:
LabVIEW 7.1
PCI 7344 Motion Controller
UMI 7764 Interface
Emerson LX 700 brushless servo drive
Emerson DXM 208 servo motor
Thanks a lot!
Malte
Malte,
the option that you are looking for is a bit hidden, but it's available in NI-Motion. I don't know your drive, but typically the drive's output current is proportional to the input voltage. This is true, if the drive is configured in current mode or torque mode, which is the recommended mode if you are using a 73xx motion control board.
In MAX there is an option to limit the output voltage of the 7344, which also limits the output current of your drive:
So e. g. if your drive outputs 3,78 V when the input voltage is + 10 V and you want to limit the output current of your drive to +/- 1 A, you should set the torque limits in MAX to +/- 2,65 V.
As I have said, current mode is the recommended mode for your drive. But even if your drive has to be configured in velocity mode for some reason, limiting the output voltage of your 7344 will help, as this would limit directly the velocity of your motor.
I hope this helps,
Jochen Klier
National Instruments
Message Edited by Jochen on 08-01-2008 10:35 AM
Attachments:
torque limits.jpg 98 KB
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I am programming a PXI-4110 with LabWindows. I am trying out the current limiting. I have an output set to 5V with a 1K load resistor; this makes the current 5mA. I set the current limit to 2mA to see it work. When I read the voltage and current it is still 5V and 5mA. Here is my code:
g_voltageLevel_ch0 = 5.0;
g_currenLimit_ch0= 2.0e-3;
status = niDCPower_ConfigureOutputFunction(vi_4110_0, channel0Name, NIDCPOWER_VAL_DC_VOLTAGE);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureSense(vi_4110_0, channel0Name, NIDCPOWER_VAL_LOCAL);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureVoltageLevel(vi_4110_0, channel0Name, g_voltageLevel_ch0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureCurrentLimit(vi_4110_0, channel0Name, NIDCPOWER_VAL_CURRENT_REGULATE, g_currenLimit_ch0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
Solved!
Go to Solution.I'm getting an error now. I have a 1K resistor on each of the outputs so I will see some current.
Look for these lines
to see comments I am sending you about the code.
When I start my program I call a function PXI4110_HardwareInit() to get things set up. This part seems to look OK.
/************************************** PXI-4110 ****************************************/
// PXI-4110 hardware definitions for initialization
static ViSession vi_4110_0 = VI_NULL, vi_4110_1 = VI_NULL, vi_4110_2 = VI_NULL;
/* The channel names are length 2 because the maximum size of the strings
from the each textbox on the UI is 1. */
static ViChar channel0Name[2] = "0"; // 0V to 6V channel
static ViChar channel1Name[2] = "1"; // 0V to 20V channel
static ViChar channel2Name[2] = "2"; // 0V to -20V channel
// inputs
ViReal64 g_voltageLevel_ch0 = 5.0;
ViReal64 g_voltageLevel_ch1 = +13.0;
ViReal64 g_voltageLevel_ch2 = -13.0;
ViReal64 g_currenLimit_ch0 = 500.0e-3;
ViReal64 g_currenLimit_ch1 = 500.0e-3;
ViReal64 g_currenLimit_ch2 = 500.0e-3;
void PXI4110_HardwareInit(void)
ViStatus status;
ViChar errorMessage[256];
ViChar resourceDCSupplyName[256] = "PXI-4110";
// set channel 0 to +5.0V
status = niDCPower_InitializeWithChannels(resourceDCSupplyName,channel0Name,VI_TRUE,VI_NULL,&vi_4110_0);
if(status < 0)
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureOutputFunction(vi_4110_0, channel0Name, NIDCPOWER_VAL_DC_VOLTAGE);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureSense(vi_4110_0, channel0Name, NIDCPOWER_VAL_LOCAL);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureCurrentLimitRange(vi_4110_0,channel0Name, 1.0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
Set_PXI_4110_Outputs();
status = niDCPower_ConfigureOutputEnabled(vi_4110_0, channel0Name, VI_FALSE);
status = niDCPower_Initiate(vi_4110_0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
static void Set_PXI_4110_Outputs(void)
ViStatus status;
ViChar errorMessage[256];
// channel 0
status = niDCPower_ConfigureVoltageLevel(vi_4110_0, channel0Name, g_voltageLevel_ch0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
status = niDCPower_ConfigureCurrentLimit(vi_4110_0, channel0Name, NIDCPOWER_VAL_CURRENT_REGULATE, g_currenLimit_ch0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
Then I send a message on ethernet to enable the outputs: When I enable the outputs this function reads the voltage and current outputs and sends this information to a application on my host computer. This information corresponds to what I set it to and what I see with a volt meter.
void PXI_4110_enable_outputs(void)
ViStatus status;
ViReal64 measuredVoltage, measuredCurrent;
ViBoolean inCompliance;
ViChar errorMessage[256];
// set the outputs
// Set_PXI_4110_Outputs();
status = niDCPower_ConfigureOutputEnabled(vi_4110_0, channel0Name, VI_TRUE);
/* Wait for the outputs to settle. */
Delay(50e-3);
// check channel 0
status = niDCPower_MeasureMultiple(vi_4110_0, channel0Name, &measuredVoltage, &measuredCurrent);
niDCPower_error_message(vi_4110_0, status, errorMessage);
niDCPower_QueryInCompliance(vi_4110_0, channel0Name, &inCompliance);
niDCPower_error_message(vi_4110_0, status, errorMessage);
Now I send a message to change the current limit. This is where I have trouble. I try and limit the current on Channel 0 to 2mA. Since the output voltage is 5Volt and the resistor is 1K the current will exceed the current limit which is what I am trying to test. I get an error in this function>
g_currenLimit_ch0 = CommandData->data;
status = niDCPower_ConfigureCurrentLimit(vi_4110_0, channel0Name, NIDCPOWER_VAL_CURRENT_REGULATE, g_currenLimit_ch0);
niDCPower_error_message(vi_4110_0, status, errorMessage);
I see g_currentLimit_ch0 = 2e-3 whic is whatI sent. but my status is a negative number. The message is "Invalid value for parameter or property"
vi_4110_0 is the handle I got earlier.
channel0Name ="0"
and g_currentLimit_ch0 = 2e-3
I do not understand why I am seeing and error here?????????????????????
thanks in advance for your help,
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http://digital.ni.com/manuals.nsf/webAdvsearch/E382785B7D67553E86256A5D0072BBE1?OpenDocument&vid=niwc&node=132100_US
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