Ultra-Fast Current Loop tech delivers speed and precision (part 2 of 2)

Ultra-fast current loop technology delivers better control through improved bandwidth and near-instantaneous feedback for end user applications that require advanced speed and precision.

If you haven’t already, please read my previous blog – part 1 in this series – The Development of Ultra-fast Current Loop Technology for more details. 

Servo drives designers have been working for decades to reach the levels of performance now seen using ultra-fast current loop technology. Servo drives have three performance loops – position, speed and current – and current is foundational, as it dictates the maximum performance of the other loops. Ultra-fast current loop is capable of sampling current more often in order to update the PWM faster and deliver higher levels of control.

The current control loop is responsible for how fast and precisely machines can operate. Increasing the gain of the speed loop allows the servo to run faster, with higher motion dynamics, a reduction in trajectory following errors and more precision in point-to-point position applications. Having achieved this, a big improvement in frequency bandwidth has been seen in the most recent generation of servos.

By delivering faster current loop performance, more applications are made possible through industrial motion control. Servo drives are selected for the speed and precision they offer and ultra-fast current loop takes this up a level to provide even greater control. As a result, ultra-fast current loop is the best option for servo applications that demand high performance, speed and precision. The technology is particularly important for controlling of certain end applications such as contouring, machines tools, printing, robotic arms and CNC machines.

Inovance’s SV670 is a high performance ultra-fast current loop servo drive.
 

Development of ultra-fast current loop technology

It has taken many years to create the right microcontrollers, IGBT, brushless motors and transducers for the development of ultra-fast current loop technology. Now that all these complementary technologies are available at the right price, today it is possible to design a servo drive with much higher performance. Inovance has always been committed to R&D and the latest trends in the design of servo drives. Keeping as a target factors such as cost, construction concept and the ergonomics of our servo drives, we have focused on the most important technical features; ease of tuning, and linear and predictable behavior.

Some high performance servo drives currently employ analog technology to achieve fast current loop. However, Inovance did it using digital technology, where the current loop algorithm calculations were executed in the form of “fast parallel computing” inside an FPGA chip. The loop calculation time was reduced to 1.6 uS cycle time (625,000 times per second), delivering comparable performance to an analog loop

The bandwidth of the current loop in top speed applications can now reach up to 4 or 5 KHz and the rejection of the loop to a disturbance is incredibly fast. For example, using modern high performance sin-cos technology encoders, we can easily reach a resolution of 23 to 25 bit (8388608 to 33554432) pulses per rev.

With this level of sensitivity every minimal movement between the body of the encoder and its shaft should produce a small output signal. Since encoders are mounted in an “elastic” way in order to absorb small play between motor shaft and motor back plain, they are prone to some mechanical mounting resonances, which can deliver spurious signals inside the current loop final stage. The ultra-fast current loop algorithm is capable of absorbing these disturbance signals and rejecting them, even at a resonance frequency of up to 5 KHz.

Industry debates analog vs digital ultra-fast current loop

Many of those within the industrial automation industry claim the best current loop is still an analog system and question whether a digital system can replace the analog current loop. Current loop in an analog arrangement is fast (with no delay) and cost effective, but there are drawbacks. 1) Analog components like resistors and capacitors are not precise, they have some value tolerance, so that, unless high-cost low-tolerance special components are used, there will be some variance in the parameters of the current loop regulator between different drives. In a digital system using numerical values it is perfectly balanced and there are no variations in production. 2) In some critical special applications it could be necessary to fine tune some parameters of the current loop, for example when using multipole motors or linear motors. This is impossible to do with an analog system since changing a parameter value requires using different values of components in the drive hardware, whereas changing parameter values in a digital system is a simple task.

Inovance has developed ultra-fast current loop technology that has so little delay and is so fast that it is fully comparable with analog performance, along with all the benefits of digital implementation, and the same levels of precision and control required from a servo drive.

Inovance servos complete with ultra-fast current loop

Complete with ultra-fast current loop technology, Inovance’s SV660N (EtherCAT), SV660F (PROFINET), IS810N (EtherCAT), SV670N (EtherCAT), SV670P (Pulse, CANopen), SV680N (EtherCAT) and SV680P (Pulse, CANopen) servos all deliver high dynamic performance with a compact footprint for a variety of industrial automation applications. In addition to the performance benefits the ultra-fast 4.5 kHz current loop technology delivers, the Inovance servo drives also come with user-friendly installation, easy set-up and tuning, and Safe Torque Off.