FAQs for SureServo AC Servo Drives

Since the release of the SureServo AC servo drives, we have compiled a list of questions that are frequently asked by our customers. The following are answers to some of those questions.

What power voltages does the SureServo require? 

The SureServo requires 220 VAC single-phase to power the smaller drives and 3-phase for larger systems. There is a 24 VDC, 500mA power supply built in to the drive for powering the inputs. If using any of the outputs, an external 24 VDC power source is needed.

How do I size and configure my system? 

AutomationDirect has teamed with one of the industry’s leaders in motor sizing software, CopperHill Technologies. Our VisualSizer-SureServo software is offered as a free download to help you select the correct servo motor and drive for your application. AutomationDirect also offers SureServo Pro configuration software as a free download, or it can be purchased on CD. Both software packages can be obtained from the SureServo.com Web site. While our technical support department is ready to help answer any questions regarding the SureServo product, the answers to most questions can be found in the SureServo manual, available as a free PDF download at SureServo.com or on the AutomationDirect technical support homepage. Example applications and a step-by-step QuickStart Guide should get most customers’ applications up and going quickly.

What modes of operation can the SureServo perform? 

SureServo can perform the following modes:

Analog torque with optional analog or preset velocity limit

Preset torque
 with optional analog or preset velocity limit

Analog velocity
 with optional analog or preset torque limit

Preset velocity
 with optional analog or preset torque limit

Pulse input
 with pulse and direction, CW/CCW, or quadrature inputs

Position Mode with Internal Indexer
. Internal parameters define the accel, speed, decel, and target position of moves. Eight unique moves can be programmed, and can all be modified via Modbus, so the system is extremely flexible. Positioning can be performed in incremental or absolute modes. In Incremental mode, the motor will move a specified distance. In Absolute mode, the motor will move to a pre-defined position.

Dual Control Mode
 allows the drive to be configured to switch on-the-fly between certain control modes. SureServo can be set for Velocity/Position Mode, Torque/Position Mode, and Velocity/Torque Modes. While in these modes, the drive can be switched from one mode to the other via a digital input signal.

Index Mode is a variation of the internal indexer and allows the servo to use STEP FORWARD/STEP REVERSE logic commands. This is useful when the application has set positions for the motor to travel. A PLC command or simple pushbutton signal tells the servo when to STEP FORWARD to the next position.

Auto Position Mode is another variation of the internal indexer that allows the servo to advance through preset positions triggered by external inputs or by automatically starting the next move after a set “dwell time”.

All of these modes are explained in detail in Chapter 6, “Control Modes of Operation and Tuning”, of the SureServo manual.

Does the SureServo support absolute positioning?

 The SureServo motors do not have an absolute encoder. However, as long as control power, which has a separate input from the main power, is maintained, the drive will keep its actual position updated. If an application is using the internal indexer, re-homing should be unnecessary. A command to go to zero will cause the motor to go to its zero position. If control power is lost, the drive’s actual position is reset to zero.

Does the SureServo offer a mechanical brake?

 Yes. Each motor size is available in a brakemotor or a non-brakemotor configuration. The motor cables are the same for both. For example, if there is a 400 watt brakemotor and a 400 watt non-brakemotor, there is only one style of motor power cable and one style of encoder cable for a 400 watt system.

How can I home the SureServo? 

SureServo allows a lot of flexibility with the homing process. Homing can be initiated by a digital input or started automatically at power-up. The servo can be programmed to home to a home limit switch, motor encoder z-pulse, or an overtravel limit switch used as a home sensor. The motor can stop at the first input or pass the input and return.

How do I communicate with SureServo? 

The SureServo drive accepts eight digital inputs that can be assigned for various functions such as Home, Reset, Trigger, Command position select, etc. There are five digital outputs such as At position, Home complete, Fault, etc. The outputs can also be configured in Indexing and Auto Position Modes to output a binary code representing Servo current position, Servo ready, Alarm, etc. All modes are explained in Chapter 6 of the SureServo manual.

Servo supports Modbus serial communication. Most parameters can be read from and written to the drive. Detailed examples of using with a DirectLOGIC PLC are demonstrated in the SureServo manual.

The servo also has a high-speed encoder output so a PLC or motion controller can monitor the system. The encoder output is scalable, allowing SureServo to emulate and replace older systems that use different motor encoder counts. For example, if an older servo system has a motor that operates at 1,000 pulses per revolution, the SureServo encoder output to the old motion controller or PLC could be scaled so that one motor revolution will send 1,000 pulses to the external controller. This is an easy way to upgrade older motion systems without having to reprogram the motion controller.

How do I use a SureServo in a PLC control system? 

The SureServo can be used with all DirectLOGIC PLCs. The PLC can issue analog velocity or torque commands to the SureServo. It can also generate high-speed output pulses using the built-in pulse outputs available on the DC output models of the DL05, DL06, and DL105 PLCs, or by using high speed I/O modules (CTRIO) available for the DL05/06, DL205 and DL405 PLC families. Another way to obtain excellent control is to use the SureServo’s built-in indexer for monitoring. With this feature, the PLC downloads position and speed commands over the serial Modbus link. Then, with a standard digital output, the PLC triggers the SureServo to move to the set position at the set speed. With this setup, a complete servo and control system can be assembled for less than $1200 when using a DL05 PLC. The SureServo manual has examples of how to set up the communication between the SureServo and aDirectLOGIC PLC.

How do I troubleshoot my system? 

While the SureServo is a very flexible and full-featured servo drive, the SureServo system has been designed so that users unfamiliar with servos will have an easy out-of-the-box experience. The SureServo manual has a step-by-step Quickstart Guide that will have the system up and running in a matter of minutes. The Quickstart Guide gives easy-to-follow steps on how to start up the system using basic configurations.

Do I have to purchase software to program the SureServo? 

You can program the SureServo two ways: 1) through the free downloadable software, or 2) through the integrated keypad. All parameters are available in the software and on the keypad. We highly recommend the software for its easy, graphical interface and the ability to use the tuning window, if necessary, to help tune the servo. While the software can be downloaded for free, you can purchase a CD version for $9. The communication cable costs $19.

Now that I know all this cool stuff, what do I need to put together a system? 

For a SureServo system you need to purchase the following five items: 1) a servo drive, 2) a servo motor, 3) a motor power cable, 4) a motor feedback cable, and 5) an I/O breakout kit which includes a breakout board and a short cable for I/O wiring to the servo. Complete systems start at less than $1,000. SureServo.com is a great resource for learning more about the product.

What accessories are offered for the SureServo systems? 

The SureServo system accessories include EMI filters, reactors, regen resistors, and communication cables. These accessories can be found at www.automationdirect.com orwww.sureservo.com/accessories.

Where can I find mechanical components for my SureServo system?

While AutomationDirect doesn’t sell gearboxes, belts, couplings, and pulleys at this time, we do provide links to several high-quality manufacturers whose components work with SureServo motors. Check out www.sureservo.com/mechanical_trans for links to gearboxes with mounting adapters for SureServo and SureStep, belts, pulleys, couplings, and more.

When do I use a servo instead of a stepper? 

The quick, easy, and most common answer is feedback. A servo system keeps track of motor command position and motor actual position. The difference between the command and the actual is called position deviation or positioning error. If the position deviation becomes too large (based on a configurable parameter), the servo will fault and report “position error” to a motion controller, PLC, and/or through the drives’ LEDs. One benefit of this arrangement is that if a servo system experiences a disturbance and gets out of position, it can recover and get “back in position”. A stepper system is much more basic in its positioning. For each pulse input into the stepper drive, the motor will be commanded to move to the next position. If the motor does not reach this position because the load or commanded speed is too great or the system gets into a bind, there usually is no feedback from the drive to the PLC/motion controller to report that the motor did not get to the correct position. The motor loses torque and the system does not recover or report that anything is wrong. Recent developments in stepper drive technology have led to hybrid steppers that do incorporate feedback. These hybrid technologies blur the line of performance and specification between steppers and servos.

Other reasons to use servos instead of steppers would be torque regulation and using an analog command signal. Typically, steppers run at full torque all the time (some have torque reduction at standstill). Servos can actually run in torque mode (where the actual torque output is based on the incoming command signal). Even when not in torque mode, a servo will output just enough torque to stay in position. Finally, steppers usually require a high-speed pulse train for a command signal. A servo will accept the high-speed pulse train as well as analog speed and analog torque command signals. The SureServo can also run its own position profile based on preset speeds and preset position setpoints.

What are the sizes offered in the servo drives and motors? 

AutomationDirect offers three servo drives that match up with eight sizes of servo motors. The smallest drive (SVA-2040) can handle our 100W, 200W, and 400W low inertia motors. Our midrange drive (SVA-2100) can power our 750W and 1kW low inertia motors and the 1kW medium inertia motor. The highest power drive (SVA-2300) connects to our 2kW and 3kW medium inertia motors. Each size of motor comes in two models: brake and no-brake (a “B” on the end of the part number represents brake). Keep in mind that all our motor power cables have the brake wires incorporated into them. Sureservo.com has specifications and descriptions to help in determining the correct drives, motors and cables to use. Charts for complete systems are found at http://www.sureservo.com/complete_systems.htm.

By Joe Kimbrell,
Motors & Drives Product Manager,

Originally Published: Dec. 1, 2007