Module No. 2 Hydraulic Drive System in Robotics PDF

Module No. 2 Hydraulic Drive System in Robotics  Hydraulic Drive Systems Linear and rotary hydraulic actuators, types of hydraulic cylinders, single acting and double acting special cylinders like tandem, rod less, Telescopic. Rotary actuators – Fluid motors, Gear, Vane and P...

Module No. 2 Hydraulic Drive System in Robotics  Hydraulic Drive Systems Linear and rotary hydraulic actuators, types of hydraulic cylinders, single acting and double acting special cylinders like tandem, rod less, Telescopic. Rotary actuators – Fluid motors, Gear, Vane and Piston motors, Motor performance, Filtration systems and maintenance.,Electrohydraulics. ▪ Robotic actuators are the "muscles" of a robot, the parts which convert stored energy into movement. ▪ They are an integral part of any robotic system. Actuators are typically powered by air, electricity, or liquids. ▪ The type of actuator used can greatly affect the performance and efficiency of the robot.  In the field of robotics, actuators play a crucial role. They are responsible for making the robot move, whether it's a simple movement like the rotation of a joint or more complex like walking or grabbing objects. Their versatility allows for a wide range of applications, from industrial automation to sophisticated humanoid robots. Without actuators, robots would be static and incapable of any movement or action. hydraulic actuators, which use pressurized fluid to create motion, are known for their high force and power. They are often used in robots that need to perform heavy-duty tasks, such as those used in construction or industrial automation settings. Hydraulic Actuator? Hydraulic actuator definition is, a device that is used to change the fluid’s pressure energy into mechanical is known as a hydraulic actuator. The hydraulic actuator includes a cylinder or a fluid motor that works through hydraulic power for mechanical operation. The mechanical motion provides an output in the form of rotary, linear otherwise oscillatory motion. When liquids are almost unfeasible to compress, then a hydraulic actuator uses a large force. The working principle of a hydraulic actuator is based on Pascal's law, which states that pressure applied at any point in a confined incompressible fluid is transmitted equally in all directions. In a hydraulic actuator, a pump pressurizes a fluid (usually oil), which is then used to move a piston. The movement of the piston can then be used to create linear or rotary motion.  A typical piston-type hydraulic actuator is shown in Below Figure. It consists of a cylinder, piston, spring, hydraulic supply and return line, and stem. The piston slides vertically inside the cylinder and separates the cylinder into two chambers. The upper chamber contains the spring and the lower chamber contains hydraulic oil. The hydraulic supply and return line is connected to the lower chamber and allows hydraulic fluid to flow to and from the lower chamber of the actuator. The stem transmits the motion of the piston to a valve. Initially, with no hydraulic fluid pressure, the spring force holds the valve in the closed position. As fluid enters the lower chamber, pressure in the chamber increases. This pressure results in a force on the bottom of the piston opposite to the force caused by the spring. When the hydraulic force is greater than the spring force, the piston begins to move upward, the spring compresses, and the valve begins to open. As the hydraulic pressure increases, the valve continues to open. Conversely, as hydraulic oil is drained from the cylinder, the hydraulic force becomes less than the spring force, the piston moves downward, and the valve closes. By regulating amount of oil supplied or drained from the actuator, the valve can be positioned between fully open and fully closed.  According to Blaise Pascal, when there is an increase in pressure at any point in a confined incompressible fluid, then there is an equal increase at every point in the container. Hydraulic actuators are designed based on this principle (Pascal’s law). To understand how hydraulic actuators work, let us take an example of two cylinders, connected together, as shown in the image. Suppose one cylinder has a cross-section area of 1 square centimeter and the second one has a cross- section area of 10 square centimeters. If the cylinders are filled with incompressible fluid and 1 unit of pressure is applied to the left cylinder pushing the pump (actually liquid) by 10 centimeter, Hydraulic actuators are majorly then the resulting force acts on the right cylinder used for systems which require very pushing the piston by 1 centimeter, but with a force large force, but not very restrictive of 10 units. This means applying 1 unit of force on positioning and accuracy. produces 10 units of force on the other side.  Hydraulic Cylinder: Generally referred as linear hydraulic motor is used when a robot requires linear force. These actuators are powered by hydraulic fluids. When hydraulic pressure acts on it, a piston connected to a piston rod within the cylinder moves back and forth creating linear motion. Hydraulic cylinders can also convert hydraulic pressure into rotation creating a rotary actuator, based on Hydraulic Robot Arm-Manipulator the mechanical design.  Researchers at Tokyo Institute of Technology (Tokyo Tech) have developed a hydraulic actuator that will allow tough robots to operate in disaster sites and other harsh environments. This figure shows a seven-axis hydraulic robot arm breaking concrete slabs, each 30 mm thick. This is a prototype for comparison with a four-legged robot also being developed in this project by Waseda University, Meiji University, and others, produced at approximately the same size. It consists of seven of the new hydraulic motors.  Boston Dynamics WildCat robot https://youtu.be/wE3fmFTtP 9g?t=88 The Boston Dynamics WildCat robot is one of the example robot working with hydraulic actuators. A robotic manipulator developed by Disney Research produces surprisingly lifelike and highly responsive motions using combined hydraulic and pneumatic systems. Rotary actuators developed by Disney Research pair rolling- diaphragm cylinders — one actuated actuated by hydraulics against one actuated by pneumatics. Click on image for larger view.  Linear Actuators Linear Actuators with complex multi-axis systems are proving to be indispensable in today’s continuously evolving industrial automation world. These systems are highly effective in positioning, handling, and transporting components quickly and reliably. Some of the many applications for linear actuator systems include machine tool, welding, painting, assembly, picking and packaging operations. To ensure machine designers can continue to meet the complex challenges of their end customers, it is important to select the proper linear actuator technology that best satisfies the application's requirements.  Hydraulic Linear actuators Hydraulic linear actuators are mechanical gadgets that transform hydraulic energy into linear motion. To generate linear motion, these actuators use pressurized hydraulic fluid to move a piston within a cylinder. Hydraulic linear actuators are gadgets that transform hydraulic fluid energy into linear motion. They are typically made up of a hydraulic cylinder and a piston that moves within the cylinder due to the force provided by the hydraulic fluid. The cylinder is usually made of metal and sealed at both ends, while the piston is attached to the cylinder through a rod that extends through one end. When hydraulic fluid is injected into the cylinder, it exerts pressure on the piston, forcing it to move linearly. This technique can be employed for activities like lifting heavy loads or pushing/pulling objects. Hydraulic linear actuators are widely utilized in industrial applications that require high force and precision control. Advantages of Hydraulic Linear Actuators Hydraulic linear actuators provide numerous advantages in terms of dependability, durability, and high-force capabilities. The following are some of their main advantages. High force and load capacity: Hydraulic linear actuators have a high force and load capacity, making them suitable for heavy-duty applications. Seamless and precise: Hydraulic systems can offer seamless and accurate motion control because of the incompressible characteristics of the fluid employed in them. Good energy efficiency: Hydraulic systems are particularly productive because they can transmit enormous quantities of power with minimum energy loss. Ability to operate in harsh conditions: Hydraulic systems are resistant to dust, grime, and other pollutants, making them excellent for use in challenging environmental conditions. Longer lifespan: Because hydraulic linear actuators have been engineered to endure enormous loads and high pressure, they are extremely durable and longer-lasting.  Applications of Hydraulic Linear Actuators Heavy machinery: Hydraulic linear actuators are widely found in bulldozers, cranes, and excavators. They are utilized to regulate the movement of the equipment's numerous elements, such as the boom, arm, and bucket. Aerospace and aviation: Hydraulic linear actuators are utilized to regulate the motion of landing gear, flaps, and other essential parts in aerospace and aviation applications. Because of their excellent reliability and capacity to survive rigorous operational circumstances, they are advocated in these applications. Industrial automation: Industrial Automating processes use hydraulic linear actuators in applications such as conveyor systems, material handling equipment, and assembly lines. They offer the high-force and precise motion control that these kinds of applications demand. Marine and offshore: Hydraulic linear actuators are employed to control the movement of different components such as rudders, propellers, and cargo handling equipment in the marine and offshore applications. They are favored because of their capacity to function in difficult situations and use great force while doing so. Agriculture industry: Hydraulic linear actuators are utilized in agricultural machinery such as tractors, plows, and harvesters. They are employed to move different components such as the blade, arm, and implement. Because of their high force capabilities and durable structure, they are advocated in the agriculture industry. Construction Industry: Construction equipment such as cranes, excavators, and backhoes use hydraulic linear actuators. They govern the movement of several components such as the boom, arm, and bucket. They are preferred because they can give great force and accurate motion control.  Automated Pick and Place Part Handling System in Workflow Robots on Rails System Fluid-Powered Rotary Actuators Fluid-powered rotary actuators, also known as pneumatic or hydraulic rotary actuators, use fluid power to rotate components. These actuators use either cylinders or rotors to convert the fluid power into rotational motion. They are typically powered by either hydraulic oil or compressed air. They are used to rotate components between 90 to 360 degrees depending on the specific requirements of the component or valve. Fluid-Powered Rotary Actuators A robotic manipulator developed by Disney Research produces surprisingly lifelike and highly responsive motions using combined hydraulic and pneumatic systems.  Fluid-Powered Rotary Actuators The system uses a series of rolling- diaphragm cylinders that use hydraulic power to move in one direction and compressed to move in the other. Two single-acting cylinders are paired to form a single rotary actuator. Essentially, force from the air cylinder creates a preload against the hydraulic cylinder. The compressed air in the one cylinder provides the return force that would otherwise be provided by a spring. Each cylinder, then, requires only one hydraulic line and one pneumatic line. The result is a system that the team describes as light, fast, and dexterous, with low friction and no backlash. Rotary actuators developed by Disney Research pair rolling- diaphragm cylinders — one actuated actuated by hydraulics against one actuated by pneumatics. Click on image for larger view.  Hydraulic Cylinders Hydraulic cylinders are essential components in various industrial applications, providing the force and motion needed to perform a wide range of tasks. From heavy machinery in construction to precise movements in manufacturing and automation, it play a crucial role. A hydraulic cylinder is a mechanical device that converts hydraulic fluid energy into linear force and motion. It consists of a cylindrical barrel, a piston, and a piston rod. When hydraulic fluid is pressurized and introduced into the cylinder, it pushes against the piston, creating a linear force that extends or retracts the piston rod. This basic mechanism is the foundation of countless applications across various industries. SYSTEM COMPONENTS HYDRAULIC PUMP Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in reaction to the load. Hence, a pump rated for 345 bar is capable of maintaining flow against a load of 345 bar. Pumps have a power density about ten times greater than an electric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coupling to reduce vibration.  SYSTEM COMPONENTS Common types of hydraulic pumps to hydraulic machinery applications are; Gear pump: cheap, durable (especially in g-rotor form), simple. Less efficient, because they are constant (fixed) displacement, and mainly suitable for pressures below 20 MPa (3000 psi). Vane pump: cheap and simple, reliable. Good for higher-flow low-pressure output. Axial piston pump: many designed with a variable displacement mechanism, to vary output flow for automatic control of pressure. Radial piston pump: normally used for very high pressure at small flows. Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half of a hydrostatic transmission.  Directional control valves route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. The spool slides to different positions in the housing, and intersecting grooves and channels route the fluid based on the spool's position. The spool has a central (neutral) position maintained with springs; in this position the supply fluid is blocked or returned to tank. Sliding the spool to one side routes the hydraulic fluid to an actuator and provides a return path from the actuator to tank. When the spool is moved to the opposite direction the supply and return paths are switched. When the spool is allowed to return to neutral (center) position the actuator fluid paths are blocked, locking it in position. Directional control valves are usually designed to be stackable, with one valve for each hydraulic Cutaway diagrams of hydraulic cylinder cylinder, actuatorsandshowing one fluidthe working input supplying all the valves component parts. in the stack.  The above is a complex circuit diagram for a hexapod robot, involving the operation of 43 pistons, using 22 valves. In this case the valves will be computer controlled and electrically operated. Imagine that the above diagram is not for a 2.5 meter robot for use in movie animation, but one of the giant defenders in Pacific Rim, in which case the rams might be as big as that below. TYPES OF LINEAR ACTUATORS  HYDRAULIC CYLINDER A Hydraulic cylinder (also called a linear hydraulic motor) is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in construction equipment (engineering vehicles), manufacturing machinery, and civil engineering. Hydraulic cylinders get their power from pressurized hydraulic fluid, which is typically oil. The hydraulic cylinder consists of a cylinder barrel, in which a piston connected to a piston rod moves back and forth. The barrel is closed on one end by the cylinder bottom (also called the cap) and the other end by the cylinder head (also called the gland) where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder into two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end / head end). Flanges, trunnions, clevises, Lugs are common cylinder mounting options. The piston rod also has mounting attachments to connect the cylinder to the object or machine component that it is pushing / pulling.  A single-acting cylinders are simple, affordable, and perfect for jobs where you only need force in one direction, like lifting Single-acting cylinders boxes or clamping things down. Single acting cylinders apply force in only one direction, typically extending the piston rod when hydraulic pressure is applied. They rely on an external force, such as a spring or gravity, to retract the piston rod when hydraulic pressure is released. Single acting cylinders are simpler in design and typically less expensive than double acting cylinders. They are commonly used in applications where the load can be moved in one direction only, such as lifting or pressing operations. There are two types of single acting cylinders: Push Type Hydraulic Cylinder – Fluid enters to push the piston out of the cylinder. This is also referred to as a hydraulic cylinder The typical applications of single acting with a ‘sprung in’ position, where the piston is fully retracted at hydraulic cylinders are simple lifting jobs, light rest. industrial and commercial applications, and any Pull Type Hydraulic Cylinder – Fluid enters to pull the piston other application where fast and consistent inside the cylinder. This is also referred to as a hydraulic cylinder retraction is not essential. with a ‘sprung out’ position, where the piston rod is fully  The double-acting cylinder has two “fluid pipes,” allowing it to Double Acting both extend and retract using hydraulic pressure. Picture a puppeteer pulling strings to control its movements, only with Cylinders hydraulic fluid instead of yarn. These dynamic cylinders are perfect for tasks where you need muscle in both directions, like opening and closing valves, moving robot arms, or operating machine tools. They’re more complex and costlier than their single-acting cousins, but their two-way power and precision make them worth the investment for many jobs. Double acting cylinders can apply force in two directions, both extending and retracting the piston rod. They have hydraulic ports at both ends of the cylinder, allowing pressurized fluid to enter and exit alternately to extend and retract the piston rod. Double acting cylinders are versatile and can be used in applications where precise control over the direction and speed of movement is required. They are often used in applications such as construction equipment, manufacturing machinery, and mobile hydraulic systems. The standard applications for double acting hydraulic cylinders are those that require repetitive presses and situations that require both pushing and pulling forces. Elevators and forklifts are good examples of double acting cylinder applications  Factors to be considered before selection of Cylinder Force and Speed Requirements: How much force is needed, and how fast does the piston need to move? Stroke Length: How far does the piston need to extend and retract? Duty Cycle: How often and for how long will the cylinder be used? Environmental Factors: Will the cylinder be exposed to extreme temperatures, dirt, or debris? Tandem Cylinder Tandem cylinders are very similar to hydraulic cylinders, which are powerful, yet simple machines that are found in numerous industrial and commercial applications. Despite having the ability to exert enormous forces, hydraulic cylinders are very simple in design. A tandem cylinder is actually composed of two hydraulic cylinders placed end to end, which makes them ideal for many applications that single hydraulic cylinders are not suited for.  A tandem pneumatic cylinder, also known as a combination cylinder, is similar to a multi force multiplying cylinder and has two pistons connected by a single rod that supply twice the force. The two components of a tandem cylinder are separate double acting cylinders connected in a series. They are used in limited space applications where higher force is needed. A tandem cylinder, shown in Fig., is used in applications where a large amount of force is required from a small-diameter cylinder. Pressure is applied to both pistons, resulting in increased force because of the larger area. The drawback is that these cylinders must be longer than a standard cylinder to achieve an equal speed because flow must go to both pistons.  Tandem Hydraulic Cylinders Used for Tandem hydraulic cylinders can be found in heavy-duty industrial applications in industries like construction, manufacturing, and agriculture. Tandem cylinders are often used in applications where a single hydraulic cylinder would not be powerful enough to get the job done, but there is not enough available space for a large hydraulic cylinder. They can also provide the same amount of power in a smaller package because there are two cylinders working together to exert high forces. These cylinders are often found on industrial vehicles. Forklift trucks, for example, often use them to raise their forks. Extremely large construction cranes often use multiple tandem hydraulic cylinders. Some of the largest and most powerful agricultural vehicles, including combine harvesters and crop sprayers, use tandem cylinders to create the high levels of sustained force that are required. Mining and excavating equipment, which is some of the largest and most powerful industrial equipment in the world, often employ these cylinder systems.  Rodless Pneumatic Cylinders Rodless pneumatic cylinders move loads along with a piston driven by compressed air. The piston is attached to a carrier where the load is mounted. The piston moves the carrier in a straight line. The direction of the piston movement is always to the side of the chamber with lower internal pressure. Rodless pneumatic cylinders offer strokes comparable to their assembly size at faster speeds. Hence, they are suitable if the overall length must be minimized due to limited space. End cushioning is necessary to prevent hard impact on the piston after full-length travel at the end caps.  Band Cylinders In band cylinders, the carrier is connected to the piston by two sealing bands that run parallel to the stroke direction. The sealing bands can be made from plastic or stainless steel. The outer band is located on top of the cylinder bore slot, which is connected to the carrier. Meanwhile, the inner band is located inside the cylinder bore, which is connected to the piston. As the carrier moves to either end, it opens the sealing band towards its stroke direction while closing the band behind the moving carrier.  Cable Cylinders In cable cylinders, the piston is connected to the carrier by a cable that passes through a pulley on each end cap. The cable is pushed by the piston in order to move the carrier. Cable cylinders are inexpensive and have a simple construction. However, cable wear causes inaccurate carrier positioning and leakage.  Magnetically Coupled Cylinder In magnetically coupled cylinders, the piston is not mechanically attached to the carrier. Instead, the carrier is moved by the piston through a strong magnetic field. Hence, air leakage is prevented since the cylinder is fully enclosed. However, the carrier may disengage from coupling and is reactive to moment loads.  Telescopic Pneumatic Cylinders Telescopic cylinders have a series of segmented tubes that extend when compressed air fills the cylinder. These tubes progressively decrease in diameter. The tube with the smallest diameter is referred to as the piston rod. Telescopic cylinders have exceptionally long strokes. The tubes consume small space when they are nested together or when the cylinder is in a retracted position. These cylinders are available in single and double acting modes. The telescopic design is more common in hydraulic cylinders than in pneumatic cylinders. Hydraulic Motors  INTRODUCTION All types of hydraulic motors have common design features: a driving surface area subject to pressure differential; a way of timing the porting of pressure fluid to the pressure surface to achieve continuous rotation; a mechanical connection between the surface area and an output shaft. The ability of the pressure surfaces to withstand force, the leakage characteristics of each type of motor, and the efficiency of the method used to link the pressure surface and the output shaft determine the maximum performance of a motor in terms of pressure, flow, torque output, speed, volumetric and mechanical efficiencies, service life, and physical configuration.  MOTOR TERMINOLOGY Motor displacement refers to the volume of fluid required to turn the motor output shaft through one revolution. Hydraulic motor displacement may be fixed or variable. A fixed-displacement motor provides constant torque. Controlling the amount of input flow into the motor varies the speed. A variable-displacement motor provides variable torque and variable speed. With input flow and pressure constant, varying the displacement can vary the torque speed ratio to meet load requirements. Torque output is expressed in inch-pounds or foot-pounds. It is a function of system pressure and motor displacement. Motor torque ratings usually are given for a specific pressure drop across the motor. Theoretical figures indicate the torque available at the motor shaft, assuming no mechanical losses. Breakaway torque is the torque required to get a stationary load turning. More torque is required to start a load moving than to keep it moving. Running torque can refer to a motor’s load or to the motor. When it refers to a load, it indicates the torque required to keep the load turning. When it refers to the motor, it indicates the actual torque that a motor can develop to keep a load turning. Running torque considers a motor’s inefficiency and is a percentage of its theoretical torque. The running torque of common gear, vane, and piston motors is approximately 90% of theoretical.  Starting torque refers to the capacity of a hydraulic motor to start a load. It indicates the amount of torque that a motor can develop to start a load turning. In some cases, this is considerably less than the motor’s running torque. Starting torque also can be expressed as a percentage of theoretical torque. Starting torque for common gear, vane, and piston motors ranges between 70% and 80% of theoretical. Mechanical efficiency is the ratio of actual torque delivered to theoretical torque. Torque ripple is the difference between minimum and maximum torque delivered at a given pressure during one revolution of the motor. Motor speed is a function of motor displacement, and the volume of fluid delivered to the motor. Maximum motor speed is the speed at a specific inlet pressure that the motor can sustain for a limited time without damage. Minimum motor speed is the slowest, continuous, uninterrupted rotational speed available from the motor output shaft. Slippage is the leakage through the motor, or the fluid that passes through the motor without performing work.  Gear motors External gear motors consist of a pair of matched gears enclosed in one housing. Both gears have the same tooth form and are driven by pressure fluid. One gear is connected to an output shaft. The other is an idler. Pressure fluid enters the housing at a point where the gears mesh. It forces the gears to rotate and follows the path of The output torque of an external least resistance around the periphery of the housing. gear motor is a function of pressure The fluid exits at low pressure at the opposite side of on one tooth because pressure on the motor. other teeth is in hydraulic balance. Close tolerances between gears and housing help control fluid leakage and increase volumetric efficiency. Wear plates on the sides of the gears keep the gears from moving axially and help control leakage.  VANE MOTORS Vane motors have a slotted rotor mounted on a driveshaft that is driven by the rotor (Fig. 5). Vanes, closely fitted into the rotor slots, move radially to seal against the cam ring. The ring has two major and two minor radial sections joined by transitional sections or ramps. These contours and the pressures introduced to them are balanced diametrically. Pressure fluid enters and leaves the motor housing through openings in the side plates at the ramps. Pressure fluid entering at the inlet ports moves the rotor Vane motors (balanced type counterclockwise. shown) have vanes in a slotted The rotor transports the fluid to the ramp openings at the outlet ports to return to tank. rotor. If pressure were introduced at the outlet ports, it would turn the motor clockwise.  The rotor is separated axially from the side plate surfaces by the fluid film. The front side plate is clamped against the cam ring by pressure and maintains optimum clearances as temperature and pressure change dimensions. Vane motors provide good operating efficiencies, but not as high as those of piston motors. However, vane motors generally cost less than piston motors of corresponding horsepower ratings. The service life of a vane motor usually is shorter than that of a piston motor, though. Vane motors are available with displacements of 20 Vane motors (balanced type in.3/rev. shown) have vanes in a slotted Some low-speed/high-torque models come with rotor. displacements to 756 in.3/rev. Except for the high-displacement, low-speed models, vane motors have limited low-speed capability  Piston-Type Motors Radial-piston motors have a cylinder barrel attached to a driven shaft. The barrel contains a number of pistons that reciprocate in radial bores. The outer piston ends bear against a thrust ring. Pressure fluid flows through a pintle in the center of the cylinder barrel to drive the pistons outward. The pistons push against the thrust ring and the reaction forces rotate the barrel. Shifting the slide block laterally to change the piston stroke varies motor displacement. When the centerlines of the cylinder barrel and housing coincide, there is no fluid flow and therefore the cylinder barrel stops. Moving the slide past center reverses the direction of Radial-piston motors have a cylinder barrel attached to a motor rotation. driven shaft. The barrel contains a number of pistons that reciprocate in radial bores.  Piston-Type Motors Radial piston motors are very efficient. Although the high degree of precision required in the manufacture of radial piston motors raises initial costs, they generally have a long life. They provide high torque at relatively low shaft speeds and excellent low-speed operation with high efficiency. Also, they have limited high-speed capabilities. Radial piston motors have displacements to 1,000 in.3/rev.