The actions of the individual joints must be controlled in order for the manipulator to perform a desired motion. The robot’s capacity to move its body, arm, and wrist is provided by the drive system used to power the robot.

The joints are moved by actuators powered by a particular form of drive system. Common drive systems used in robotics are electric drive,
hydraulic drive, and pneumatic drive.

Types of Actuators
*Electric Motors, like: Servomotors, Stepper motors or Direct-drive electric motors
*Hydraulic actuators
*Pneumatic actuators

Drive Systems
The drive system determines the speed of the arm movement, the strength of the robot, dynamic performance, and, to some extent, the kinds of application.

Robot Actuators Quality
Have enough power to acc/dec the links, Carry the loads, Light, Economical, Accurate, Responsive, Reliable and Easy to maintain.

Characteristics of Actuating Systems
*Weight, Power-to-weight Ratio.
*Operating Pressure.
*Stiffness vs. Compliance.
*Use of reduction gears.

Stiffness vs. Compliance
Stiffness is the resistance of a material against deformation. Hydraulic systems are very stiff and noncompliant. Pneumatic systems are compliant.

*The stiffer the system, the larger load that is needed to
deform it.
*The more compliant the system, the easier it deforms under
the load.
*Stiffness is directly related to the modulus of elasticity of the
material.
*Stiff systems have a more rapid response to changing loads
and pressures and are more accurate.
*A working balance is needed between these two competing
characteristics.

Use of Reduction Gears
Gears used to increase the torque and reduce the speed. Hydraulic actuators can be directly attached to the links. This Simplifies the design, Reduces the weight, Reduces the cost, Reduces rotating inertia of joints, Reduces backslash, Reduces noise and Increases the reliability of the system.

Electric motors normally used in conjunction with reduction gears to increase their torques and to
decrease their speed. This increases the cost, increases the number of parts, increases backslash, increases inertia of rotating body, increases the resolution of the system.

Applications
Electric motors are the most commonly used actuators. Hydraulic systems were very popular for large robots. Pneumatic cylinders are used in on/off type joints, as well as for insertion purposes.