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Load cell feedback

  • Hi,


    I'm looking to mount a load cell onto the end of a kuka KR210 and use it to apply a load to an object. Eg say 500N needs applied. I want the robot to move down and the load cell to tell the robot that 500N is reached and move up.


    Any help in how to do this would be much appreciated

  • AD
  • there are special input modules for load cell or strain gauge (for example EL3356-0010).


    But KUKA does not support every module out there, specially things that may be configurable, so ... unless you are certain that such module is supported by KUKA, i would say forget it and use regular 16-bit analog input on the robot side and use external load cell controller. note, there is quite a selection of controllers out there and they can have different features such as display with keypad, analog output type (4..20mA, 0-10V) and digital outputs for reached limit. this means it can be possible to interface it without analog I/O.


    as far as program goes, just use interrupt to stop robot when value is reached. this has been beaten to death on the forum so feel free to explore.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Hi


    Could you provide some controllers that would work with the kuka. i have EL4001 output module on the kuka so any help would be appreciated

  • The EL4001 is an output module. For the robot to read the load cell inputs, you would need (at minimum) at analog input module. And what module you used would depend in large part on what communications options your KRC has installed.


    Load cells usually output microvolts, which a regular analong input module would be unable to measure accurately. So your load cell needs some sort of amplifier to bring its output up to an industrially useful voltage. The most common industrial analog signals are -10 to +10V, 0-10V, and 4-20mA.


    Whatever voltage or current range your load cell amplifier outputs, you will need an analog input module that is both compatible electrically with that signal range, and compatible with whatever communications options your KRC has.

  • Perhaps I should explain the system in a it more detail. Essentially I have an s type load cell mounted to to tool flange and a bar attached to the load cell to just get reach and apply the load. I want the robot the move in a set direction and then stop when a certain force is reached. From previous replies on this post the load cell needs an amplifier due the the micro volts given out by a load cell. The output from the amplifier is wired into in input module in the kuka.


    Is the load read in voltage by the kuka and to set an load, does a voltage need to be applied in order or can then kuka be set to keep moving until a voltage is reached.

  • you get the sensor wired to and input, configure robot so that input is mapped and refreshed. write program that responds to input.

    as mentioned before you need either specific type of analog input if you want to connect such sensor directly. not sure if they are supported though. issue is that standard digital I/O are easily supported but when it comes to analog (specially analog that need parametrization through software) this may not work or if it works, it will likely be the default settings. this is why it is safer bet to stick to units known to be supported such as analog modules that can be obtained through KUKA. so if you cannot get straight answer from KUKA and don't want to experiment yourself, than is safer to avoid specialized analog I/O for load cell input and go with regular analog input that is known to be supported (but in this case you will need to add transducer/amplifier). and even that means you need to pay attention (need to match, for example transducer may have a differential output etc.).


    KUKA has a list of supported modules that is on Xpert. not sure if if free Xpert access can get you to that list though.if i recall, standard input card is EL3162 which is dual 0-10V single ended 16-bit input module

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Is the load read in voltage by the kuka and to set an load, does a voltage need to be applied in order or can then kuka be set to keep moving until a voltage is reached.

    Voltage from where to where?


    The load cell needs excitation voltage, but that should be provided from the load cell amplifier. The amplifier will need a power supply.


    The analog input module on the robot will need a power supply of its own, but generally only two wires (one for reference/ground, one for signal) to the amplifier. Those two wires are for the signal only, and do not supply power.

  • What if i was to use the HX711 analogue to digital converter which is commonly used in to amplify load cell signals and would go into digital inputs on the kuka. Still not sure if this would work. I have seen the hx711 used with an ardunio which handles the calibration of the load cell and the reading of the load cell. has anyone seen the kuka working with the ardunio

  • what if you read datasheets of both devices and compare specs (voltage, timing etc.)


    for example that device uses I2C interface. this is not electrically compatible with robot I/O. another issue is that robot I/O speed is low. they are filtered and chocked by bus update rate and software interpolation time - something MCUs dont have to deal with


    in comparison I2C works at 100000 bps or so. bit-banging with robot I/O (assuming you used proper level converter) will get you up to screaming speeds as high as 80bps

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Before we could advise you at all on what analog input module to use, you would have to tell us what model KRC you have, what KSS it is running, and what option packages it has installed. As called out in the READ FIRST topic at the top of the forum.


    What sort of amplifier you can use depends entirely on what your load cell is compatible with. Normally, load cells come with a matched amplifier.


    And no, you cannot connect an analog output (from the amp) to a digital input (on the robot). It might not cause any harm electrically, but it would not produce any usable result.

  • If the arduino runs a program which sets a digital Output pin on the arduino to an digital input pin on the robot. The EL1809 '0' voltage is -3 to 5V and '1' voltage is 11 to 30V. 5v output can us stepped up to 12V to trigger a 1 on the digital output. The robot program of this could a an until loop which moves robot until a 1 is triggered.


    Let me know if I'm on the right track

  • Any digital input on the robot is likely to be based around the industry-standard 24VDC signal voltage. So, as Panic says, an optocoupler or relay would be needed between the Arduino and the input module.


    The relay would ideally be SPDT, and connect the digital input directly to its own 0V line when open, and switch it directly to the module's 24V reference when closed. Most (most!) industrial digital-input modules are designed to be "shorted" directly to 0V or 24V, to be used with direct-contact buttons, switches, etc. So unlike wiring an Arduino, there's no "pull up" or "open-collector" type issues to be concerned with.

  • just make sure to consider Vco of the optos output. some devices are low voltage but there is plenty of products that can handle 30+ volts.

    one rather common product is PC817 for example.

    https://www.farnell.com/datasheets/73758.pdf


    next thing to note is that like all things in life, proper polarity and bias are needed... both on input and output side. on the input side it is enough to add resistor in series with the LED in optos input (10mA is plenty so 470 Ohm if using 5V, or 220 Ohm if using 3.3V controller.


    output side should have correct polarity as well. KRC input is expecting PNP so opto need to be wired as a high side switch. this means Collector to +24V and Emitter to robot input. to be able to test it without robot. you may add LED and 10k resistor from emitter to 0V. observe current transfer ratio and loading of the opto by KRC input or just go for version with Darlington output.


    example circuit with high side output:


    Optocoupler Circuits | Nuts & Volts Magazine

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Hi,


    you are talking all the time about voltages.


    Start with the sensor. What is the sensor outputting (force and torque given in voltages, or just voltage and you have to calculate the forces and torques by yourself)?


    Or are you looking for a simple sensor only supplying one force value? The same question as above


    regards


    MOM

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