Closed Loop technologyTechnology paper

Closed-loop compatible stepper motors combine the advantages of stepper and servo motor technologies. They run more smoothly and with less resonance than stepper motors, yet they afford position feedback and control along with short transient and free oscillation times, and they do not suffer a loss of steps. Closed-loop compatible stepper motors provide an alternative to stepper motors where the situation demands

The closed-loop process is also called sinusoidal commutation via encoder with field-oriented control. The heart of closed-loop technology is power-adjusted current regulation and feedback of control signals. Encoder signals report the rotor position and sinusoidal phase currents are generated in the motor windings. Vector control of the magnetic field ensures that the magnetic

Some stepper motors are adorned with the closed-loop label and work with encoders, yet lack field-oriented control with sinusoidal commuted current regulation. Such motors monitor only the step position, but cannot correct step angle errors during operation. A real closed-loop field-oriented control compensates for step angle errors during motion and corrects load angle errors within one full step.

energy efficiency, smoothness and high load tolerance. Compared to servo-motors, closed-loop compatible stepper motors have advantages due to high torque at low RPM, short transient times, correct positioning without convergence, lower price, and often smaller size.Closed loop is explained briefly here:http://en.nanotec.com/dc_408_technology_closedloop.html

field of the stator is always perpendicular to that of the rotor and that the field strength corresponds precisely to the required torque. The current regulated in this way in the windings ensures uniform motor power and extremely quiet operation of a motor that can be precisely controlled.

gClosed Loop Technology

gWhat is a closed loop?

gTrue vs. pseudo Closed Loop

Open Loop vs. Closed Loop

controller stepper motor load

Open Loop: no positioning control, no error correction

regulator stepper motorcontroller

Closed Loop: position control with field-oriented regulation

W X

load

sensor

Classical stepper motors are reliable, economical drives that can be used for travel to fixed positions. They operate in open-loop mode, where control signals are not fed back. The lack of position feedback is thus a limitation because, e.g., step offset or step loss due to overload is not detected.

Energy efficiency

Overload

Service life

Resonance behavior

In an open-loop system, the stepper motor is dimensioned such that it is certain to move the maximum required load. For this reason, normally a safety factor of 20% is calculated, which amounts to wasted energy in the application. When the load is reduced, the open-loop motor cannot react and wastes even more energy.

With a 20% safety reserve and a design for a continuous load of 20 kg, an additional load of only 5 kg exceeds the power reserve and the open-loop drive stops without an error message. By contrast, with its overload reserve the closed-loop stepper motor can handle this load increase easily.

Efficient power regulation generates less heat in the motor, which stays significantly cooler. Reduced heating protects the motor bearings.

Resonance frequencies occurring in the open loop depend on external loads (the greater the torque reserve, the greater is the resonance stimulation) and can bring the motor to a stop. In closed-loop mode, the motor receives only as much energy as needed for the external load; the torque reserve and its resonance stimulation do not exist, so there is practically no resonance behavior.

Furthermore, lower frequencies induce more resonance behavior, and a small increase in load or a torque peak causes the motor to lose steps or fall out of synchronization or even to stop completely.

gAdvantages over standard stepper motors

n No calculation or purchase of a safety reserve (normally up to 50%) required

n Greater efficiency on load fluctuation and no stoppage on overload

n Energy-efficient operation due to intelligent current regulation

n Practically resonance-free

n Longer service life of bearings due to less heat and vibration

n Reduced acceleration time because high torque is achieved even at high RPM

n Precise positioning due to monitoring and correction

Closed Loop Stepper Motors are an advanced development of classical stepper motor technology.They eliminate the limitations and drawbacks of classical stepper motors:

Open Loop

Open Loop

Open Loop

Open Loop

Closed Loop

Closed Loop

Closed Loop

Closed Loop

Closed-loop step motors by Nanotec frequently provide an alternative to servo-drives, e.g., for winding tasks and conveyor belt operation. Not only can the rotational velocity and the position be more precisely controlled, but also (as typically required for winding applications) the torque

(torque mode). Closed-loop stepper motors combine the benefits of both worlds, achieving the greatest maximum torque, the highest efficiency and the best dynamics as well as the least torque ripple and exceptionally quiet operation.

gAdvantages over servo-motors

n High torque at speeds up to 500 rpm and a compact, economical solution without gearbox

n Rapid commissioning without expensive tuning

n Load held in position

n Avoidance of transient and free oscillation behavior (hunting), which is typical of servo-motors and occurs especially on variable loads and pulsation, leading to intolerable step errors for the application (on sudden load changes, servo-motors miss their positions and must be corrected)

Closed-loop compatible stepper motors provide an alternative when the application requires:

In torque mode the closed-loop stepper motor functions analogously to a spring, whereby the spring tension characteristic curve can be set via a potentiometer. Thus the motor delivers a stable force, even when the motor counteracts a force while the motor is stopped. When the force declines, the motor begins to turn proportionally to the declining force up to the current and torque setpoint values. Thus the closed-loop stepper motor proves ideal for any type of winding, stretching and pressing applications.

A2 rewinding the label band via torque mode

A1 unwinding of label spool in torque mode

A3 label application

S1 edge sensorS2 edge of label for trigger sensor

A4 conveyor belt for product

C

Drive C could handle a printing job

F=5N

I1

I2

I3

I4

Md

n

torq

ue

load

RPM

I1

I2

I3

I4

v - Md (current)

constant draw

brake

n Multiple axis applications (serial, Ethernet, EtherCAT, CANopen)

n Positioning tasks with load fluctuation

n Winding

n Conveyor belt (start/stop, positioning)

n Dosing pumps, filling systems

n Semiconductor assembly

n Wafer production

n Textile machines, industrial sewing machines

n Robotics

n Inspection systems

n Applications that require quiet operation, short transient time and precise positioning

Linear axis (for processing, assembly, etc.)

Decentralized flow regulation

Conveyor belt

Winding and installation

g Ideal application domains for Closed Loop Stepper Motors

START

Input1 GNDGND AnalogInput6 +20V+20V

3

3

1

1

2

2

+20VGNDa) Input 6b) Input 6

v = 0,5 m/s

p = 4

b

s0

h

F = 10N +/-25%

+20V In 3

a)

A1

A2

b)

Out 3 GNDGND+5V +UBAna GND GND

3

2

1

+

X3 Motor Communication

X2 Power Motor

+UB+

GND

+UB

GND

X11

X12

X10 USB

Input 1 (Start or Error)

Input 6 (Limit Switch orclock in Clok/Dir Mode)

Input

0%outout 1 out 2

100%

exte

rn in

tern

X21

Con

nect

or

Net

wor

k

X5 External I/O

X8 +5V+UB +5V

X9 a

nalo

g

2

2(BCD)( 1 )

( 2 )

( 3 )

( 7 )

( 10 )

2 2

R6

- Limit Switch- busy- ready- Rotation monitoring

20 1 2 3

3 4 5

Input 2 - 5 (Drive Profil)

pull/up out3 X14

X4 Motor I/O

- - - - - - -

- - - - - - - - - - - - - -

- - - - - - -

- - - - - - -

input 1 input 2 input 3 input 4 input 5 input 6

X1 Power In

X20

conn

ecto

rco

mm

unic

atio

nne

twor

k

x7 CAN

www.nantotec.com

X6 RS485

ZIB2 - PDX - N

GND+UBGND+UBGND+UBGNDANAOUT3OUT2OUT1GNDIN6IN5IN4IN3IN2IN1

GNDIN1IN2IN3IN4IN5IN6

GNDOUT1OUT2OUT3

ANAGND

GND+TX+

TX-RX-

RX+CAN+CAN-GND

UB_extGND

1 2 output R18

1

1

2 3 4 5 6

S1

R19

R20

D8

1 2 3 4 5 6

weon

SIL

ABS

CP21

02DC

F07X

1104

+

0611001 6W

101

2 2><

2 2><

C2

START

b) Input 6

Input 1

S1

4

5 (on)

GND

a) Input 6

+20V

PD4-N59 Plug & Drive stepper motor with closed loop

Servomotor DB57 with controls and gearbox

Price per motor approx. 325.00 $ 142.00 $

Price per control approx. 203.00 $

Price per gearbox approx. 85.00 $

Total price 325.00 $ 430.00 $

Nanotec Electronic U.S. Inc., 98 Sheridan Avenue, Medford, MA 02155, Phone 781 219 3343, Fax: 781 498 1344E-mail: info@us.nanotec.com, www.nanotec.com

gComparison (example)