A servo motor is a rotary actuator that uses feedback to control its rotational position very accurately. At a basic level, a servo motor consists of a motor coupled to a sensor for position feedback. This can be an optical encoder that tracks the motor's revolutions and position.
Servo motors work in a closed-loop control system with a controller that receives feedback from the encoder. The controller compares the actual position to the target and makes small corrections by adjusting the motor's power until the positions match. This allows servos to achieve much higher precision than open-loop systems.
Common types of servo motor include coreless and brushed DC motors as well as brushless DC motors. Coreless DC servos provide torque at low speeds but can suffer from vibration and heat. Brushed DC servo motors are rugged and affordable but require more maintenance. Brushless variants have no brush erosion issues and are highly efficient.
By design, servo motors are optimized for applications that demand precise control over rotational position, such as robotics, 3D printers, CNC machines, and automation equipment. Most standard servo systems work within a rotation range of 180-720 degrees.
Factors like gearing and mechanical load affect how far a servo can rotate reliably. Heavy loads mean the motor must work harder, drawing more current and generating heat quickly. To prevent overheating, the duty cycle and available cooling dictate the upper rotation limits. Lighter loads allow higher rotation ranges.
Some servo motors are specifically built to sustain continuous indefinite rotation instead of intermittently moving between set positions. These continuous rotation servos differ in their internal configuration and drive control approach.
Rather than position control geared for short moves, continuous rotation servos employ velocity control that maintains a constant commanded speed. Feedback focuses on matching the target rpm through torque adjustments independent of absolute position. As long as cooling is adequate and load torque doesn't cause stalling, the servo can rotate endlessly.
Continuous rotation servos suit various industrial processes requiring tight speed regulation better than standard AC motors. Common uses include:
Conveyor belts & rolls: Maintain constant belt/roll velocities for synchronized product handling.
Material handling: Feed filaments, fibers, or sheets at exact rates in conversion machinery.
Processing equipment: Regulate speeds of mixers, blenders, pumps and similar rotating components.
Grinding/polishing: Finely tune abrasive tool rpm for consistent, defect-free surface finishing.
Laser systems: Synchronize scanning mirrors and lenses with laser sources through precise speed coordination.
While capable of continuous rotation, these servos have some limitations compared to standard variants:
Increased costs due to specialized construction for continued high-load operation.
Potentially larger size from additional cooling components like fans and heat sinks.
Strict thermal management is critical to prevent overheating during indefinite high-torque loads.
Application machinery may require redesign to leverage continuous rpm control capabilities.
Maximum rated speeds are typically lower than intermittent-duty servos for longevity.
Thoroughly considering rotational needs, ambient temperatures, cooling accessibility, and expected duty cycles helps ensure continuous rotation servos can perform reliably over the long term.
With careful modifications, a standard servo motor can potentially operate continuously:
Configure the drive in velocity mode using encoder feedback to regulate speed.
Improve cooling with heatsinks, fans, or liquid systems to efficiently reject excess heat.
Use thermal sensors to regulate motor torque/current at elevated temps automatically.
Reinforce the motor mechanically to withstand higher operating temperatures.
Establish duty cycle limits preventing overload based on thermal time constants.
However, modifications increase failure risks, so it's generally safer and more cost-effective to use purpose-built continuous rotation servos specifically rated for indefinite runs if prolonged turns are required.
In conclusion, while designed chiefly for intermittent profiling, continuous rotation is achievable from some servo motors through adaptation of their control and cooling to suit constant-speed operation needs. This versatility broadens servo technology applications.