Robot Drives ctuatorsahshjwjjsjjajjsj.pp

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1. Robot Drives and Actuators

2. Introduction: Various transmitting elements are employed to drive the mechanical links to a desired position and orientation. The power is transmitted or applied to various joints of the robot through gears, belts cable chains etc.

3. Basic drive systems: Hydraulic Drive Pneumatic Drive Electrical Drive ( a.c . and d.c. Motors) Electrical Stepper Motors

4. Factors for Drive Selection: Power Consumption Positional Accuracy Repeatability Speed of Operation Stability Reliability Cost Open Loop Control Closed Loop Control, etc.

5. Hydraulic Cylinder: A partial vacuum is created at the inlet of the pump. The fluid enters the pump when the piston moves towards the left as shown.

6. Hydraulic Pump: When piston moves towards the right, the outlet check valve opens and the discharge occurs through the outlet pipe.

7. Pump Classification: Hydrodynamic or Non-Positive Displacement Pumps Hydrostatic or Positive Displacement Pumps

8. Hydrodynamic or Non-Positive Displacement Pumps: There are two pumps in this category: 1. centrifugal (impeller) pump, 2. axial (propeller) pump There is sufficient clearance between the rotating and stationary elements. The flowrate depends on the speed of propeller or impeller and resistance at outlet More the restriction, lesser the discharge Some fluid leaks backward past the rotating element When the outlet is completely closed, volumetric efficiency falls to zero

9. Hydrostatic or Positive Displacement Pumps Delivers a fixed quantity of fluid per revolution of pump shaft. If resistance to the flow increases, pressure may rapidly build up A pressure relief valve is therefore provided Output flow increases with increase in speed Gear pumps, vane pumps and piston pumps fall in this category

10. Gear Pump As the gear turns, the size of chamber at inlet becomes larger creating vacuum Atmospheric pressure in the tank forces the fluid into the void. At the outlet, the volume decreases between the meshing teeth. Pump casing has leak proof internal seal Gear pump is sometimes provided with side wear plate

11. Vane Pumps: Main elements are pump housing, vanes and rotor Vanes are fitted in radial slots on rotor Rotor rotates inside the housing and the vanes slide in and out of the slot Rotor is located eccentrically inside the housing As rotor rotates, vane comes out due to centrifugal force,, volume of space between rotor and housing increases, and pressure drops creating vacuum. Pump sucks the fluid during first half revolution and discharge during the second half.

12. Variable displacement vane pump: A pressure compensator or handwheel is used to move the cam ring to change the eccentricity. Self adjusting pump and prevent excessive pressure build up Output varies with demand of fluid or load When eccentricity is maximum, flow is maximum and when eccentricity is zero, flow is zero.

13. Radial Piston Pumps: Very similar to vane pump It has radially located pistons which move in and out due to rotational motion of rotor Oil is drawn into the piston during outward movement During inward movement, discharge takes place

14. Axial Piston Pump: Drive shaft of the pump is connected to the cylinder block through universal joint The cylinder block rotates with the driving shaft Cylinder block has a valve plate attached to one end The valve plate has two openings, one for inlet and other for outlet The cylinder block is set at an angle of offset rotating to the axis of drive That’s why the pumps are called as bent axis axial piston pumps The piston rods are connected to the drive shaft flange through ball and socket joint The offset angle can vary from zero to any angle to vary the displacement of pump

15. Swash Plate Axial Piston Pump