Automated Processes and Servomechanisms

Summary

An automated process is a series of sequential steps to be carried out automatically. Servomechanisms are systems, devices, and subassemblies that control the mechanical actions of robots by the use of feedback information from the overall system in operation.

Definition and Basic Principles

An automated process is any set of tasks that has been combined to be carried out in a sequential order automatically and on command. The tasks are not necessarily physical in nature, although this is the most common circumstance. The execution of the instructions in a computer program represents an automated process, as does the repeated execution of a series of specific welds in a robotic weld cell. The two are often inextricably linked, as the control of the physical process has been given to such digital devices as programmable logic controllers (PLCs) and computers in modern facilities.

Physical regulation and monitoring of mechanical devices such as industrial robots is normally achieved through the incorporation of servomechanisms. A servomechanism is a device that accepts information from the system itself and then uses that information to adjust the system to maintain specific operating conditions. A servomechanism that controls the opening and closing of a valve in a process stream, for example, may use the pressure of the process stream to regulate the degree to which the valve is opened.

The stepper motor is another example of a servomechanism. Given a specific voltage input, the stepper motor turns to an angular position that exactly corresponds to that voltage. Stepper motors are essential components of disk drives in computers, moving the read and write heads to precise data locations on the disk surface.

Another essential component in the functioning of automated processes and servomechanisms is the feedback control systems that provide self-regulation and auto-adjustment of the overall system. Feedback control systems may be pneumatic, hydraulic, mechanical, or electrical in nature. Electrical feedback may be analogue in form, although digital electronic feedback methods provide the most versatile method of output sensing for input feedback to digital electronic control systems.

Background and History

Automation begins with the first artificial construct made to carry out a repetitive task in the place of a person. One early clock mechanism, the water clock, used the automatic and repetitive dropping of a specific amount of water to accurately measure the passage of time. Water, animal, wind-driven mills, and threshing floors automated the repetitive action of processes that had been accomplished by humans. In many underdeveloped areas of the world, this repetitive human work is still a common practice.

With the mechanization that accompanied the Industrial Revolution, other means of automatically controlling machinery were developed, including self-regulating pressure valves on steam engines. Modern automation processes began in North America with the establishment of the assembly line as a standard industrial method by Henry Ford. In this method, each worker in his or her position along the assembly line performs a limited set of functions, using only the parts and tools appropriate to that task.

Servomechanism theory was further developed during World War II. The development of the transistor in 1951 enabled the development of electronic control and feedback devices, and hence digital electronics. The field grew rapidly, especially following the development of the microcomputer in 1969. Digital logic and machine control can now be interfaced in an effective manner, such that today's automated systems function with an unprecedented degree of precision and dependability.

How It Works

An automated process is a series of repeated, identical operations under the control of a master operation or program. While simple in concept, it is complex in practice and difficult in implementation and execution. The process control operation must be designed in a logical, step-by-step manner that will provide the desired outcome each time the process is cycled. The sequential order of operations must be set so that the outcome of any one step does not prevent or interfere with the successful outcome of any other step in the process. In addition, the physical parameters of the desired outcome must be established and made subject to a monitoring protocol that can then act to correct any variation in the outcome of the process.

A plain analogy is found in the writing and structuring of a simple computer programming function. The definition of the steps involved in the function must be exact and logical, because the computer, like any other machine, can do only exactly what it is instructed to do. Once the order of instructions and the statement of variables and parameters have been finalized, they will be carried out in exactly the same manner each time the function is called in a program. The function is thus an automated process.

The same holds true for any physical process that has been automated. In a typical weld cell, for example, a set of individual parts are placed in a fixture that holds them in their proper relative orientations. Robotic welding machines may then act upon the setup to carry out a series of programmed welds to join the individual pieces into a single assembly. The series of welds is carried out in exactly the same manner each time the weld cell cycles. The robots that carry out the welds are guided under the control of a master program. This program defines the position of the welding tips, the motion that it must follow, and the duration of current flow in the welding process. This is done for each movement, along with many other variables that describe the overall action that will be followed. Any variation from this programmed pattern of movements and functions will result in an incorrect output.

The control of automated processes is carried out through various intermediate servomechanisms. A servomechanism uses input information from both the controlling program and the output of the process to carry out its function. Direct instruction from the controller defines the basic operation of the servomechanism. The output of the process generally includes monitoring functions that are compared to the desired output. They then provide an input signal to the servomechanism that informs how the operation must be adjusted to maintain the desired output. In the example of a robotic welder, the movement of the welding tip is performed through the action of an angular positioning device. The device may turn through a specific angle according to the voltage that is supplied to the mechanism. An input signal may be provided from a proximity sensor such that when the necessary part is not detected, the welding operation is interrupted and the movement of the mechanism ceases.

The variety of processes that may be automated is practically limitless given the interface of digital electronic control units. Similarly, servomechanisms may be designed to fit any needed parameter or to carry out any desired function.

Applications and Products

The applications of process automation and servomechanisms are as varied as modern industry and its products. It is perhaps more productive to think of process automation as a method that can be applied to the performance of repetitive tasks than to dwell on specific applications and products. The commonality of the automation process can be illustrated by examining a number of individual applications, and the products that support them.

Repetitive tasks are to be carried out in the same way, in the same circumstances, and for the same purpose a great number of times. The ideal goal of automating such a process is to ensure that the results are consistent each time the process cycle is carried out. In the case of the robotic weld cell described above, the central tasks to be repeated are the formation of welded joints of specified dimensions at the same specific locations over many hundreds or thousands of times. This is a typical operation in the manufacturing of subassemblies in the automobile industry and in other industries in which large numbers of identical fabricated units are produced.

Automation of the process, as described above, requires the identification of a set series of actions to be carried out by industrial robots. In turn, this requires the appropriate industrial robots be designed and constructed in such a way that the actual physical movements necessary for the task can be carried out. Each robot will incorporate a number of servomechanisms that drive the specific movements of parts of the robot according to the control instruction set. They will also incorporate any number of sensors and transducers that will provide input signal information for the self-regulation of the automated process. This input data may be delivered to the control program and compared to specified standards before it is fed back into the process, or it may be delivered directly into the process for immediate use.

Programmable logic controllers (PLCs)first specified by the General Motors Corporation in 1968have become the standard devices for controlling automated machinery. The PLC is essentially a dedicated computer system that employs a limited-instruction-set programming language. The program of instructions for the automated process is stored in the PLC memory. Execution of the program sends the specified operating parameters to the corresponding machine in such a way that it carries out a set of operations that must otherwise be carried out under the control of a human operator.

A typical use of such methodology is in the various forms of computer numeric control (CNC) machining. CNC refers to the use of reduced-instruction-set computers to control the mechanical operation of machines. CNC lathes and mills are two common applications of the technology. In the traditional use of a lathe, a human operator adjusts all of the working parameters such as spindle rotation speed, feed rate, and depth of cut, through an order of operations that is designed to produce a finished piece to blueprint dimensions. The consistency of pieces produced over time in this manner tends to vary as operator fatigue and distractions affect human performance. In a CNC lathe, however, the order of operations and all of the operating parameters are specified in the control program, and are thus carried out in exactly the same manner for each piece that is produced. Operator error and fatigue do not affect production, and the machinery produces the desired pieces at the same rate throughout the entire working period. Human intervention is required only to maintain the machinery and is not involved in the actual machining process.

Servomechanisms used in automated systems check and monitor system parameters and adjust operating conditions to maintain the desired system output. The principles upon which they operate can range from crude mechanical levers to sophisticated and highly accurate digital electronic-measurement devices. All employ the principle of feedback to control or regulate the corresponding process that is in operation.

In a simple example of a rudimentary application, units of a specific component moving along a production line may in turn move a lever as they pass by. The movement of the lever activates a switch that prevents a warning light from turning on. If the switch is not triggered, the warning light tells an operator that the component has been missed. The lever, switch, and warning light system constitute a crude servomechanism that carries out a specific function in maintaining the proper operation of the system.

In more advanced applications, the dimensions of the product from a machining operation may be tested by accurately calibrated measuring devices before releasing the object from the lathe, mill, or other device. The measurements taken are then compared to the desired measurements, as stored in the PLC memory. Oversize measurements may trigger an action of the machinery to refine the dimensions of the piece to bring it into specified tolerances, while undersize measurements may trigger the rejection of the piece and a warning to maintenance personnel to adjust the working parameters of the device before continued production.

Two of the most important applications of servomechanisms in industrial operations are control of position and control of rotational speed. Both commonly employ digital measurement. Positional control is generally achieved through the use of servomotors, also known as stepper motors. In these devices, the rotor turns to a specific angular position according to the voltage that is supplied to the motor. Modern electronics, using digital devices constructed with integrated circuits, allows extremely fine and precise control of electrical and electronic factors, such as voltage, amperage, and resistance. This, in turn, facilitates extremely precise positional control. Sequential positional control of different servomotors in a machine, such as an industrial robot, permits precise positioning of operating features. In other robotic applications, the same operating principle allows for extremely delicate microsurgery that would not be possible otherwise.

The control of rotational speed is achieved through the same basic principle as the stroboscope. A strobe light flashing on and off at a fixed rate can be used to measure the rate of rotation of an object. When the strobe rate and the rate of rotation are equal, a specific point on the rotating object will always appear at the same location. If the speeds are not matched, that point will appear to move in one direction or the other according to which rate is the faster rate. By attaching a rotating component to a representation of a digital scale, such as the Gray code, sensors can detect both the rate of rotation of the component and its position when it is functioning as part of a servomechanism. Comparison with a digital statement of the desired parameter can then be used by the controlling device to adjust the speed or position, or both, of the component accordingly.

Social Context and Future Prospects

While the vision of a utopian society in which all menial labor is automated, leaving humans free to create new ideas in relative leisure, is still far from reality, the vision becomes more real each time another process is automated. Paradoxically, since the mid-twentieth century, knowledge and technology have changed so rapidly that what is new becomes obsolete almost as quickly as it is developed, seeming to increase rather than decrease the need for human labor.

New products and methods are continually being developed because of automated control. Similarly, existing automated processes can be reautomated using newer technology, newer materials, and modernized capabilities.

Particular areas of growth in automated processes and servomechanisms are found in the biomedical fields. Automated processes greatly increase the number of tests and analyses that can be performed for genetic research and new drug development. Robotic devices become more essential to the success of delicate surgical procedures each day, partly because of the ability of integrated circuits to amplify or reduce electrical signals by factors of hundreds of thousands. Someday, surgeons will be able to perform the most delicate of operations remotely, as normal actions by the surgeon are translated into the miniscule movements of microscopic surgical equipment manipulated through robotics.

The advent of artificial intelligence (AI) is poised to fundamentally change manufacturing processes and the delivery of services. This is particularly the case in automated processes involving predictive maintenance, quality assurance, and other forms of optimizations. AI, nonetheless, does contain inherent risks that must simultaneously be addressed. This especially pertains to potential ethical abuses of new AI-driven applications. One example, as it pertains to automated processes, is how large data sets of human-specific data is mined, analyzed, and put to use.  This especially pertains to potential ethical abuses of new AI-driven applications. Others caution on what can be exaggerated expectations of what AI technology can actually provide.

Concerns that automated processes will eliminate the role of human workers are unfounded. The nature of work has repeatedly changed to reflect the capabilities of the technology of the time. The introduction of electric street lights, for example, did eliminate the job of lighting gas-fueled streetlamps, but it also created the need for workers to produce the electric lights and to ensure that they were functioning properly. The same sort of reasoning applies to the automation of processes today. Some traditional jobs will disappear, but new types of jobs will be created in their place through automation.

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