Robot Actuators

Actuators are used in order to produce mechanical movement in robots. Actuators for Robots Actuators are used in order to produce mechanical movement in robots. Slides from Braunl and Jussi Suomela Jussi Suomela HUT/Automation

Not only electrical actuators Pneumatic Hydraulic chemical

Hydraulic and Pneumatic Motors Pneumatic Power - Air-powered cylinders Compressed air Either stored on board or injected by a pump Produces linear motion through activation of cylinders Hydraulic Power - Fluid (non-air)-powered cylinders Uncompressible fluid, most often oil. Requires a pump to generate the pressure and flow rate needed. Complex and difficult to build effectively, and costly.

Hydraulic and Pneumatic Motors Double Acting Cylinders Air Inlet Piston rod Double Acting Cylinder Retracted Mechanical Stops Air Inlet Extended Extension limit Stroke

Pneumatic Actuators Jussi Suomela HUT/Automation

Pneumatic Devices  It is very similar to hydraulic system, but power-to-weight ratio is much lower than hydraulic system.  Because the air is compressible, it compressed and deforms under load.

Pneumatic Actuators like hydraulic except power from compressed air fast on/off type tasks big forces with elasticity no leak problems Jussi Suomela HUT/Automation

Double Action Cylinder

Single Action Cylinder Compressed air Compressed air Single Action Cylinder Double Action Cylinder

Hydraulic Actuators Jussi Suomela HUT/Automation

When we use liquid as the fluid, we call it a hydraulics system

Hydraulic Actuators Components and Properties linear movement big forces without gears actuators are simple in mobile machines Bad efficiency motor, pump, actuator combination is lighter than motor, generator, battery, motor & gear combination Jussi Suomela HUT/Automation

Hydraulic Valves servo valves proportional valves complicated structure, expensive good control proportional valves simple, cheap robust more difficult to control Digital hydraulics, new! several fast on/off valves (2n) digital control of the flow Jussi Suomela HUT/Automation

Hydraulic actuators: cylinders Cylinder types: Double acting piston: Single acting: work can be done only in one direction Work is done in both directions Plunger Piston rod on both sides Piston Tandem Telescopic Telescopic Fast moving Fast moving 2005/2006 I. Hydraulic and Pneumatic Systems

Servo Valve Jussi Suomela HUT/Automation

Advantages of Hydraulic Actuators  Hydraulic Actuator offers: a high power-to-weight ratio , large forces at low speeds compatibility with microprocessor tolerance of extreme hazardous environments. torque where, A is the effective area of the piston, p is the working pressure.

Comparing Electrical and Fluid Actuators

A simple hydraulic system can be made out of syringes and aquarium tubing

A simple ROV with a hydraulic actuator

Click the two links below to see some simple but effective hydraulic systems in action: http://www.youtube.com/watch?v=VFje0G69ku8&feature=related http://www.youtube.com/watch?feature=endscreen&v=vsF95qA1x7I&NR=1

For ideas on building a linear actuator with a motor and some PVC, check out this link: http://blog.davidjbarnes.com/2009/03/making-linear-actuator-for-robots.html

Applications of Hydraulic Motors

Arska

Hydraulic actuators

Workpartner

Actuators are Everywhere - Examples

Other Actuators piezoelectric magnetic ultra sound SMA inertial Jussi Suomela HUT/Automation

Comparison of various Actuators Jussi Suomela HUT/Automation

Advantages and Disadvantages of Hydraulic Actuators

Advantages and Disadvantages of Pneumatic Actuators

(DC motor and stepper motor) Advantages and Disadvantages of Electric Actuators (DC motor and stepper motor)

Motors Properties: Comparison

Practically In this class we will use only servos In past we used DC motors with H-bridge, pneumatic actuators, nintinol wires and hydraulic actuators. So far, if you want to build rather small robots and you want to concentrate on intelligence and sensing, RC servos are the best choice. Many new types arrive every year, from very small to big powerful ones. Look to internet. We will learn about some new actuators if time will allow at the end of the class.

What did we learn? Feedback control is a fundament of robot control Various kits (Lego Dacta Control Lab) have several demonstrations and project to explain the principles of feedback: Line following Speed control Temperature control (fan, lamp, sensor)

What did we learn? Control of Many DOF robots is tough In addition to classical and modern control theory we use: fuzzy control genetic algorithms neural control bio-mimetic systems Review your control knowledge (for next quarter), but remember that in this class all knowledge is through programming

Your task Learn about the particular servo that you plan to use. If the servo was not suggested by the professor, learn about servos that are available, calculate your project requirements for a servo and pick one. Ask Bryce to order for you. The more servos we order, the cheaper the price of one. If you do not want to use one of standard servos, your choices are: build your own servo from a DC motor. This is a big project by itself and you must have clear reasons to do so Use AC motor. Only for big robots. The same as above. Use stepper motor. Remember that they are slow and weak, why you want to use them? You must be sure of your reasons

Your task Use hydraulic control. Why? You need to purchase or build your own actuator. Think about redesigning our horse leg with better syringes and oil instead of water. How can you connect the syringe to a stepper motor? Use pneumatic control. Read first the documentation of pneumatic hand or old Electric Horse. Talk to designers. Find pistons in Mondo-Tronics or other robot store. They are good. Use Nintinol or other similar actutors. They are good for face muscles or similar small and weak movements. Can they be used for a hexapod? I doubt, but try to convince me Before you do this, read the two-volume book of Conrad and Mills

Sources Braunl Jussi Suomela Jussi Suomela HUT/Automation