Stepper Motors are essentially open loop systems working efficiently when required to produce torque. However, when the motor faces low torque situations, its efficiency falls drastically. By simply closing the current loop, it is possible to make the entire system operate more efficiently.
Users find them to be economical as stepper motors offer the advantages of excellent positioning with their simplicity. This feature makes them highly popular for use In general automation tasks such as positioning, indexing, inserting, feeding, and more. Now, with closed loop operations, users are finding stepper motors equally adequate for applications involving force and torque control.
Optimizing the operational performance requires users to understand certain characteristics of stepper motors. Traditionally, users operate stepper motors in open loop control. That means the drive electronics has no feedback regarding the torque the motor has to handle at any time. Therefore, the drivers continuously supply full load current even when the motor has no load to drive. The excess load current heats up the motor, reducing the efficiency of the system.
Such operation of stepper motors in open loop systems tends to classify them as inefficient devices because of the loss of power involved. However, this is not true, as stepper motors are highly efficient when called upon to deliver torque, only losing their operational efficiency when not driving a load. The problem is readily solved by providing a feedback to control the amount of current the motor actually requires for handling the present load.
Manufacturers have noticed the benefits of closed loop operation and offer integrated motors that produce higher torque, greater throughput, faster acceleration rates, reduced noise, and higher operational efficiency. These motors have a built-in closed loop system to reduce the input current to the motor automatically as the load reduces.
Such closed loop systems commonly employ a feedback device, usually an incremental encoder, for monitoring the error between the present shaft position as against its commanded position. The drive electronics runs algorithms to control motor current dynamically based on the error information from the feedback device.
The above process tends to reduce the overall current consumption, thereby saving power over conventional open loop stepper motor systems and improving the efficiency of the system greatly. The improvement is readily demonstrated by comparing the power consumption between two stepper motors, one operating in open loop and the other in a closed loop system.
A comparison of power consumption between the two motor systems driving identical loads shows the closed loop system will consume only a third of the power taken in by the traditional open loop stepper motor system for doing the same work. This proves the closing of the current loop results in the stepper motor operating with less power, improved efficiency, and lower costs. This also results in lower downtime, as there is a drastic reduction in motor heating.
Closed loop systems offer additional benefits apart from higher energy efficiency. A stepper motor operating in a closed loop offers faster acceleration and greater throughput because of the higher peak torque it generates—nearly 1.5 times its rated holding torque. The motor also runs more quietly.