Robot Actuators Actuators for Robots Actuators are used

Robot Actuators

Actuators for Robots Actuators are used in order to produce mechanical movement in robots. Slides from Braunl and Jussi Suomela HUT/Automation 2

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 Piston rod Retracted Air Inlet Mechanical Stops Double Acting Cylinder Extended Stroke Air Inlet Extension limit

Pneumatic Actuators Jussi Suomela HUT/Automation 6

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 ulike hydraulic except power from compressed air ufast on/off type tasks ubig forces with elasticity uno leak problems Jussi Suomela HUT/Automation 8

Double Action Cylinder

Compressed air Single Action Cylinder Double Action Cylinder Compressed air

Hydraulic Actuators Jussi Suomela HUT/Automation 11

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

Hydraulic Actuators Components and Properties o linear movement o big forces without gears o actuators are simple o in mobile machines o Bad efficiency o motor, pump, actuator combination is lighter than motor, generator, battery, motor & gear Jussi Suomela HUT/Automation combination 13

Hydraulic Valves q servo valves qcomplicated structure, expensive qgood control q proportional valves qsimple, cheap qrobust qmore difficult to control q Digital hydraulics, new! qseveral fast on/off valves (2 n) qdigital control of the flow Jussi Suomela HUT/Automation 14

Hydraulic actuators: cylinders Cylinder types: Double acting piston: Single acting: work can be done only in one direction Plunge r Work is done in both directions Piston rod on both sides Piston Tandem Telescop ic 2005/2006 I. Fast moving Telescop ic Hydraulic and Pneumatic Systems Fast moving 15

Servo Valve Jussi Suomela HUT/Automation 16

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=VFje 0 G 69 ku 8&feature=related http: //www. youtube. com/watch? feature=end screen&v=vs. F 95 q. A 1 x 7 I&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/m aking-linear-actuator-for-robots. html

Applications of Hydraulic Motors

Arska

Hydraulic actuators

Workpartner

Actuators are Everywhere - Examples

Other Actuators l l l piezoelectric magnetic ultra sound SMA inertial Jussi Suomela HUT/Automation 28

Comparison of various Actuators Jussi Suomela HUT/Automation 29

Advantages and Disadvantages of Hydraulic Actuators

Advantages and Disadvantages of Pneumatic Actuators

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

Motors Properties: Comparison

Practically l In this class we will use only servos l In past we used DC motors with H-bridge, pneumatic actuators, nintinol wires and hydraulic actuators. l 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. l We will learn about some new actuators if time will allow at the end of the class.

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

Your task l 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. l 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 l 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? l 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. l 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 HUT/Automation 39