A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.
PLCs were first developed in the automobile manufacturing industry to provide flexible, ruggedized and easily programmable controllers to replace hard-wired relays, timers and sequencers. Since then, they have been widely adopted as high-reliability automation controllers suitable for harsh environments. A PLC is an example of a “hard” real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.
A Human-Machine Interface (HMI) is a user interface or dashboard that connects a person to a machine, system, or device. While the term can technically be applied to any screen that allows a user to interact with a device, HMI is most commonly used in the context of an industrial process.
A servomotor is a closed-loop servomechanism that uses position feedback to control its motion and final position. The input to its control is a signal (either analogue or digital) representing the position commanded for the output shaft.
The motor is paired with some type of encoder to provide position and speed feedback. In the simplest case, only the position is measured. The measured position of the output is compared to the command position, the external input to the controller. If the output position differs from that required, an error signal is generated which then causes the motor to rotate in either direction, as needed to bring the output shaft to the appropriate position. As the positions approach, the error signal reduces to zero and the motor stops.
The most commonly used robot configurations are articulated robots, SCARA robots, delta robots and cartesian coordinate robots, (gantry robots or x-y-z robots). In the context of general robotics, most types of robots would fall into the category of robotic arms (inherent in the use of the word manipulator in ISO standard 8373). Robots exhibit varying degrees of autonomy:
- Some robots are programmed to faithfully carry out specific actions over and over again (repetitive actions) without variation and with a high degree of accuracy. These actions are determined by programmed routines that specify the direction, acceleration, velocity, deceleration, and distance of a series of coordinated motions.
- Other robots are much more flexible as to the orientation of the object on which they are operating or even the task that has to be performed on the object itself, which the robot may even need to identify. For example, for more precise guidance, robots often contain machine vision sub-systems acting as their visual sensors, linked to powerful computers or controllers. Artificial intelligence, or what passes for it, is becoming an increasingly important factor in the modern industrial robot.
Electrical control panels are designed and used to control mechanical equipment. Each one is designed for a specific equipment arrangement and includes devices that allow an operator to control specified equipment.
Electrical panel components control every piece of equipment in every industry. It’s difficult to describe all possible combinations because every industry and most companies have defined component preferences.
If you need to come up to speed on control panels fast, take your time. Find someone to help you, someone who knows what you’re trying to do. Start with the basics and build from there. Below are the basics.
Light curtains fall into a category of equipment known as presence detection devices. Other common presence detection devices are pressure-sensitive safety mats and laser scanners (often used on Remotely Operated Vehicles (ROV) when in industrial settings). Most important applications of safety relays are in automation industries dealing with robotic cell setup.
Light curtains are supplied as a pair with a transmitter and receiver. The transmitter projects an array of parallel infrared light beams to the receiver which consists of a number of photoelectric cells. When an object breaks one or more of the beams a stop signal is sent to the guarded equipment.
The light beams emitted from the transmitter are sequenced, one after the other, and pulsed at a specific frequency. The receiver is designed to only accept the specific pulse and frequency from its dedicated transmitter. This enables the rejection of spurious infrared light and thus enhances their suitability as components within a safety system.
Typically, light curtains are connected to a safety relay which will remove motive power from the hazard in the event that an object is detected. Safety relays can be provided with muting functionality which enables the temporary disabling of the safety function to allow objects to pass through the light curtains without tripping the safety relay. This is particularly useful for machinery which has some semi-automatic procedures.
The design technology is the main difference between the safety relays and regular relays:
- Classic contact-based relay technology “force-guided contacts relay”
- With electronic evaluation and contact-based volt-free outputs
- Fully electronic devices with semiconductor outputs
Safety relays must always be designed in such a way that, if wired correctly, neither a fault in the device nor an external fault caused by the sensor or actuator will lead to the loss of the safety function.