Servo Motor Controls

Positioning Stage delivers precision motion control.

August 2, 2011 - Single Rail Stage, SRS-006-04-030A, can generate 30 lb at 100% Duty Cycle and has 3-phase, brushless, linear motor as well as U-shaped magnet assembly. Used in closed-loop positioning applications, open type positioning stage has ironless core coil assembly. Linear guidance is achieved using one linear rail with 1 or 2 linear recirculating ball bearing guides, and non-contact glass, metal, or magnetic scale linear encoders are used for position feedback. H2W engineers have developed a new Single Rail Stage (SRS-006-04-030A) that is capable of generating 30 pounds at 100% Duty Cycle. The SR stage is a compact, small footprint, open type positioning stage. It is used in closed loop positioning applications that require high speed and high accelerations of lighter loads. The ironless core coil assembly has no magnetic attractive force to the stationary magnet assembly, which reduces the load on and increases life of the bearing system. The low overall weight of the stage makes it ideal as a Y axis (top axis) in a multi-axis system. The lower moving mass of the stage allows for much higher accelerations of light payloads. The stage includes a three-phase brushless linear motor. The short encapsulated moving coil assembly moves thru a gap in the long "U" shaped magnet assembly. A customer supplied bearing system is required to guide the moving coil assembly and to maintain a .025 in [0.63 mm] clearance between the magnet and the coil assembly. The power to the motor (from a customer supplied PWM 3-phase brushless servo amplifier) is supplied to the moving secondary via a power cable. Larger motors with higher forces are available, consult factory for details and drawings. There is a long stationary "U" shaped magnet assembly made with nickel-plated steel back iron and Neodymium permanent magnets. The magnets are bonded to the 2 parallel steel plates and the plates are bolted to a steel spacer bar. Threaded and thru holes are available in the steel back iron for mounting the magnet assembly to the customer supplied base plate. The length of the magnet assembly is a function of the stroke. The Single Rail Stages incorporate state of the art high quality linear motion products. Linear guidance is achieved by using a single linear rail with 1 or 2 linear recirculating ball bearing guides. The bearing is sealed with wipers to contain the lubrication and to keep out debris. A non-contact glass, metal, or magnetic scale linear encoders are used for position feedback, which includes a reference mark for homing. Multiple reference marks are available and are spaced every 50 mm down the length of the scale. Typical encoder output is A and B square wave signals but sinusoidal output is available as an option. End of travel limit switches are included at both ends of the stroke. The switches can be either active high (5V to 24V) or active low. The switches can be used to shut down the amplifier or to signal the controller that an error has occurred. The limit switches are typically an integral part of the encoder, but can be mounted separately if required. Cable guidance is achieved by using a cable carrier. Cable carriers are over sized to allow for routing of customers hoses and cables. Hard stops are incorporated into the ends of the stage to prevent over travel damage in the event of servo system failure. (TNN). TNN is a comprehensive source of new and timely product information in the industrial marketplace. TNN supplies new product information to the web sites, e-marketplaces and print publications that serve the industrial marketplace. For press release submissions please go to http://news.thomasnet.com/submitpr.html . BY ACCESSING, BROWSING AND/OR USING THIS WEB SITE AND/OR ANY WEB SITES PROVIDED BY ProductNews.com, YOU AGREE TO BE BOUND BY THE TERMS OF USE AGREEMENT .

How servo control drives help in controlling the servo motors ...

Servo control is an important and essential part of a servo motor as it controls its motion by transferring a pulse of variable width. The servo control drive is the main component that remains connected to the motor via a control cable. The parameters that are pertaining for this pulse signals include minimum and maximum pulse and a repetition rate. The servo has a number of rotational constrains therefore neutral is set as the position where the servo acquires the same quantity of potential rotation both in the clockwise and anti clockwise direction. When calculating the movement it is important to remember that different servos have different constraints on their rotation but all of them have the same equal position.

Now comes the most imminent question as to what role do servo control drives have to play in this?  The angle of the movement gets determined by the servo controls. This is done by identifying the duration of a pulse and then applying it to the control wire that connects the drive to the motor. This procedure is name as Pulse width Modulation.

The servo expects a pulse reading of 20 ms per second. It is the length of each of the pulse that will determine to what extent the motor will turn. For example, a 3.0 ms pulse produced from the servo control will allow the motor to turn to 180 degree position which will be its neutral position.

When the servo control drive sends command to the motor for moving in a particular direction, they will move to the instructed position and will stay put at the same position till further commands are served. The highest quantity of force that a servo can exert is actually reads the torque rating of the servo. Servos will however not keep on holding to their position forever. The servo control has to give out the position pulse to instruct the servo for its next move.

When a pulse signal gets sent by the servo control drive to a servo, the servo rotates to a point and holds on to its output shaft at a degree that is counterclockwise from the unbiased point.

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