reaction force of water jet

  • Does anyone have any information about reaction force due to water jet on static load torque / Allowable MOI on wrist unit?

    Robot is used for high pressure water jet cleaning (9 - 10MPa).

    I need to know the effect of back force generated on wrist unit, Means there should be some limit depending on static load torque/allowable MOI of wrist unit.

    Any help will be highly appreciated.

  • AD
  • The force will depend on a large number of variables -- pressure, orifice size, jet velocity, angle vs gravity, just to name a few. You're probably going to have to measure the force empirically to get an accurate value. The manufacturer of the cutter should have some approximate values that might be good enough for you to use.

  • Thanks for your help.

    In general case we always take care of COG values and weight of EOAT.

    But what about the reaction force of water jet on wrist unit on the time of water on and in running condition ?

    I mean, reaction force of water + weight of EOAT ; must be less than static load torque and Allowable MOI of wrist. Is it right ?

    If yes, how to calculate the reaction force of water.

    Pr : 10MPa

    Orifice Dia : 1.3mm

    Allowable static load torque for wrist :

    1. J4 : 16.6 N-m

    2. J5 : 16.6 N-m

    3. J6 : 9.4 N-m

    Allowable MOI for wrist :

    1. J4 : 0.47 Kg.m2

    2. J5 : 0.47 Kg.m2

    3. J6 : 0.15 Kg-m2

  • For a calculation, you'd have to estimate the change in momentum of the water exiting the nozzle. This could produce a force value.

    However, water jets are usually very small diameter. Lots of pressure, but how much mass is being expelled per unit time? Water jet manufacturer could give guidance on volumetric flowrate of water+abrasive (and THAT gives mass flow rate for momentum calculation).

    I suspect that this is a lot of unnecessary calculation. Arms large enough to perform large waterjet cuts will usually be large payload also. They might not ever notice the waterjet reaction force. Small arms may be more susceptible to those forces.

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