Design Techniques for Efficient Power Transmission
Power transmission refers to the transfer of mechanical power from one component or machine to another. It is essential in manufacturing and production environments, where different machines and equipment need to work together to produce goods efficiently. Power transmission in modern industrial automation is achieved when electric motors transmit power through various mechanical systems, including gears, belts, chains, and couplings.
In a manufacturing plant, a motor may power a conveyor belt that transports materials from one machine to another. The power transmitted through the motor is transferred to the conveyor belt through a gear system, which allows for smooth and efficient power transmission. This article highlights typical applications for power transmission along with the types of motors and drives that are commonly used.
Typical power transmission applications include the following:
Conveyor systems: Widely used in manufacturing and material handling applications to move products or materials from one location to another. Power transmission drives the conveyor belts, rollers, and other components of the conveyor system.
Industrial robots: Used in a variety of automation applications, including material handling, assembly, and welding. Power transmission transfers mechanical power from the robot’s motors to the joints and end-effectors.
Machine tools: Power transmission drives the spindles of lathes, milling machines, and grinders that shape and finish metal parts.
Packaging machinery: Packages products for distribution and sale. Power transmission runs the conveyors, fillers, cappers, and other components of the packaging machinery.
Printing machinery: Power transmission propels the rollers and other components of the machinery that print labels, packaging, publications, and other materials.
Material handling equipment: Cranes, hoists, and lifts move heavy materials or products.
There are several common types of motor and drive systems used in power transmission, depending on the specific application and requirements.
AC induction motors are the most common type of motor in power transmission applications. They are simple, reliable, and efficient, making them suitable for a wide range of applications. The typical speed range of an AC induction motor varies depending on the design and application of the motor. However, most AC induction motors have a speed range of 900 to 3,600 revolutions per minute (RPM) at full load.
In general, AC induction motors operate at a constant speed that is determined by the frequency of the power supply and the number of poles in the motor. For example, a 60 Hz power supply and a four-pole motor would result in a synchronous speed of 1800 RPM. The actual operating speed of the motor, however, may be slightly lower than the synchronous speed due to slip, which is the difference between the synchronous speed and the actual rotor speed.
The speed of an AC induction motor can be controlled by varying the frequency of the power supply, typically using a variable frequency drive (VFD). This allows the motor to operate at speeds below and above its synchronous speed, providing greater flexibility in controlling motor speed and torque.
The typical speed regulation of an AC induction motor depends on several factors, including the design of the motor, the load characteristics, and the control method used. Generally, AC induction motors can maintain speed within a certain percentage of their rated speed, typically ranging from ±0.1 percent to ±10 percent of the rated speed, depending on the control system used. Some specialized AC induction motors, such as high-speed motors used in centrifugal compressors or fans, may have a different speed range. These motors can operate at speeds of up to 15,000 RPM or higher.
DC motors are often used in applications that require precise speed control or when high torque is required at low speeds. They are driven using a direct current (DC) power source, which provides a constant voltage to the motor’s terminals. The voltage causes current to flow through the motor’s windings, creating a magnetic field that interacts with the permanent magnets inside the motor. The interaction between the magnetic fields causes the motor’s armature (rotor) to rotate.
The direction of rotation is determined by the direction of the current flowing through the windings, which can be controlled using a DC motor controller. The DC motor controller can vary the voltage supplied to the motor, which affects the motor’s speed and torque. By adjusting the voltage, the controller can also manipulate the direction of the motor’s rotation. In general, DC motors can operate at speeds ranging from near zero to tens of thousands of RPM.
There are two basic types of DC motors: brushed and brushless. Brushed DC motors have a commutator and brushes that transfer electrical power to the motor’s windings, while brushless DC motors use an electronic commutation system that switches the current to the motor’s windings in a precise sequence. Brushless DC motors are becoming increasingly popular in industrial automation applications due to their high efficiency, low maintenance requirements, and precise control capabilities.
Servo motors and stepper motors are two examples of brushless DC motors. They are often used in applications that require precise motion control in addition to efficient power transmission. The term power transmission generally refers to the transfer of mechanical power from one component or machine to another, rather than precise control of position. Motion control, on the other hand, involves the use of specialized components and systems to precisely control the position, velocity, and acceleration of the machine or system.
Motion control systems typically include brushless DC motors, encoders, and specialized controllers, which work together to achieve highly precise and accurate positioning. Motion control is often used in applications that require highly accurate positioning, such as robotics, CNC machines, and other precision manufacturing equipment. By contrast, power transmission is often used in applications where precise positioning is less critical, such as material handling and conveying systems.
Servo motors provide higher precision and accuracy than stepper motors, due to closed-loop feedback systems that continuously monitor and adjust the servo motor’s position, speed, and torque to maintain the desired performance. Stepper motors, on the other hand, often operate in an open-loop system that can experience positioning errors due to missed steps or other factors. Servo motors are capable of higher speeds and acceleration rates than stepper motors due to the servo motor’s ability to operate at higher frequencies.
Servo motors provide better control with high loads than stepper motors. This is because servo motors have higher torque capabilities, which allow them to maintain their position and speed even under heavy loads. On the other hand, servo motor systems generally cost more than stepper motor systems. For this reason, it is common to see stepper motors used in lower speed, lower performance applications, for example, when replacing pneumatic actuators.
One example of an application that exhibits both efficient power transmission and precise motion control is a servo press. A servo press is a type of industrial machine which uses a servo motor to control the position and speed of a steel rod as it applies high force to a material or part being worked on. The rod of the servo press is mechanically coupled to the servo motor through a precision ball screw and nut assembly.
When the servo motor turns the ball screw, the nut and rod extend (or retract) with both high positional accuracy and high force. The force generated by the servo press can range from a few hundred Newtons on smaller servo presses to a hundred-thousand or more Newtons on larger servo presses. Every servo press comes with a force transducer affixed to the end of the rod. The force transducer accurately measures the force generated by the servo press and provides feedback to the press controller. The press controller uses the force feedback to generate the required force repeatedly and accurately. In this way the servo press also performs a quality control function.
Servo presses, like the YJKP Servo press kit from Festo, are used in a wide range of assembly and fabrication processes, such as clamping parts together, inserting one part into another, punching a hole into a part, riveting, bending or stamping parts, and much more. At the heart of the servo press kit is a ball screw linear actuator that efficiently transfers power from the servo motor to the workpiece, while the press controller and servo motor accurately control the position and speed of the rod end.
Power transmission is critical in industrial automation as it enables machines to work together seamlessly, reducing downtime and maximizing productivity. Without proper power transmission, machines may not function correctly, leading to delays in production and other operational inefficiencies. It enables the efficient transfer of mechanical power from one machine or component to another and plays a vital role in ensuring the smooth functioning of manufacturing and production processes.
Motion control is a form of power transmission that provides precise positioning of the system in addition to the efficient transmission of power from the motor to the mechanical system.
This article was written by Eric Rice, Product Market Manager — Electric Automation, Festo (Islandia, NY). For more information, visit here .
This article first appeared in the June, 2023 issue of Motion Design Magazine.
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