The makeup of a drive system constitutes an actuator system fitted together with a robot’s arm or leg. These actuators, applicable in robotics, are of three primary types: electric, hydraulic, and pneumatic. Additionally, the combination of the three is useful when the requirements are for an appropriate custom setting. The article takes an analytical look at the robotic drives and the mechanisms behind their functionality.
New types of actuators or electric motors are under rapid development. They include the printed circuit disc motors, the linear induction motors, and the stepping motors. The fast development statistically caused an outburst increase in the shares of the electric drives from 12.7% to 50% between 1977 and 1990. Under the same period, the pneumatic drives’ stock dropped from 45% to 10%. The importance of hydraulic drives cannot be an underestimation; they contribute as the primary power source of the robots, hence their involvement in high lifting capacity scenarios. The appearance of pneumatic servomotors newly founded solutions over the past few years, however, is a chance for the drives of this sort to acquire redemption.
The Pneumatic Drives
The applicability of compressed air as an entity of compressed fluids is a necessary need for the functionality of the pneumatic drives. These drives have the upper hand because of there abundant availability. Moreover, the ease of access to air (power medium), whose release is after finalizing a task, is another advantage. On a comparative scale to the hydraulic drives, the pneumatic drives have a high safety mark during operations.
Additionally, the differentiating factor of other fluids from compressed air is that air has high compliance (low stiffness) and zero viscosity characterizing it with better dynamic properties. The areas that make use of pneumatic drives can be in primarily small and simple performance tasks like pick-and-place. The operational pressure of a typical system under compressed air can be 0.4 + 0.8 MPa.
The actuator can be of a linear or rotary kind. The functional overview of the drive can have the following breakdown:
- A two-position four-way valve supplies air to the actuator.
- A pneumatic or electric logic system controls the valve.
- The end-stops piston is in place due to a logical signal transmitted by limit switches.
- The system primarily operates under two positions.
It is possible to program the cycle duration if the pneumatic manipulator equips itself with such drives. However, the pneumatic manipulator should be characteristic of two-position joints, and a manual change of the displacement range should come to effect. The inexpensively described system, however, comes with less flexibility in comparison to a proportional system.
A two-stage amplifier characterizes the system’s design. The impact piston amplifier is the first part, and the air transmitter is the second and is responsible for a depicted large volume flow. Feedback provision is through an error signal. Two springs are in place to ensure a balance between the feedback and the pistons’ positions. A controller can also function as a pneumatic control system if the bellows arrangement is under modification under an integrating or differentiating option.
A pneumatic PID controller can be the result of such modifications. The actuation of a robot’s prismatic joint can be the functionality of each controller. A cylinder and a four-way valve represent the hydraulic system. A turbine motor can also play a role in actuating a rotary joint. The controllers’ output pressure Po thus should be of the same proportions to the motor’s generated torque. The torque and pressure, however, should be independent of the lever’s velocity.
Thus, the quickness and accuracy in the joint movements are through high-pressure compressed air. The individual joints also need mechanical end-stops. The use of hydraulic actuators should come to play when there is the need to maintain a constant load trajectory and high-lifting larger loads.
