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Festo Top 10 Tips For Electric Drive Automation[1]


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Festo Top 10 Tips For Electric Drive Automation[1]

  1. 1. Top 10 tips on selecting and installing Electrical Drive Automation solutions Size from end effector Mounting servo & stepper Select your stepper card upwards motors onto mechanical carefully When considering a handling axis Remember if you are using a system of any type, always When considering mounting stepper motor system and work from the end effector servo and stepper motors on you want to use micro (gripper or vacuum) upwards. to mechanical axis, ensure stepping, your step pulse Firstly size the gripper, then you allow for misalignment. from your PLC or stepper any rotary actuator Flexible couplings such as card must be able to keep up requirements. After this, size “Oldham” type or bellows, with your performance the vertical (Z axis) and then couplings are ideal. expectations. i.e. a typical any horizontals (X and Y stepper motor may have 200 axis). steps per revolution. If you want smoother and more Minimise quantity of precise motion you can of bearings in multi axis course on most systems go solutions to 32nd step micro stepping. If your requirement is for a This now gives 6,400 steps multi axis solution, the best per revolution. practice is to reduce the These usually come supplied amount of bearings between with set screw fixing or If you want to rotate at 900 the rigid frame and the clamping. They also act as a rpm, it requires 5,760,000 product. By keeping this to a mechanical fuse. If the drive pulses per minute which is minimum (5 bearings crashes, the coupling slips 96,000 pulses per second or absolute maximum) you and therefore minimised 96khz. You must ensure this minimise the cumulative expensive damage to the can be achieved. This is often deflection and therefore ballscrew or belt drive. The overlooked by the improve accuracy. Also, if the ideal solution is to select a mechanical designer when axes are electrical, problems manufacture that can supply sizing the system as they do are compounded as high play the axis, coupling housing, not deal directly with the PLC and deflection effects the coupling, flange and motor. specification. tuning of the axis and This minimised the risk and produces an unstable gives a guaranteed solution. system. Festo Ltd Caswell Road Brackmills Trading Estate Northampton NN4 7PY Tel: (0800) 626422 Fax: (01604) 667001
  2. 2. Benefits of stepper & What is inertia mismatch Avoiding unnecessary servo motors ratio? strain & wear on drive Stepper motor technology is Most stepper and servo belts & bearings often thought of as the poor systems are sized not on the When linking two axes cousin in motion control torque requirement but on together in a parallel terms when compared with the inertia requirement configuration, ensure the servo. This is often a (although torque is an coupling shaft between the misconception as, although important factor). If a motor axes is mounted on the same the dynamics are lower than is attached to a load that has shaft as the motor. This servo, a correctly sized a much higher inertia than ensures rigid power stepper system can offer the rotor (rotating part of the transmission and guarantees major cost benefits over a motor), the load will tend to the two axes run together in servo. Remember to oversize drive the motor and not the a synchronous manner. a stepper by at least 30%, to other way round (a little like Mounting the coupling shaft ensure it never loses steps a smart car pulling a 2 tonne on the opposite end of the and you will have a very caravan). This is not a good axis to motor introduces a lag reliable and cost effective situation to be in and and additional strain on the system. If in doubt, always therefore it is important to belt and bearings. seek advice from a ensure the load inertia is not manufacturer that offers both too high in relation to the technologies and you will be rotor inertia. assured of a non-biased optimum solution. In most simple positioning tasks, this inertia can be up to 10: 1 (load:rotor). A CNC machine that requires very precise positioning throughout its movement would have an inertia match of perhaps 1:1. If the load inertia is too high, a gearbox can be fitted which Servo motor will help considerably in reducing this ratio (a 4:1 gearbox will reduce the inertia of the load by nearly 16 times). Stepper motor Festo Ltd Caswell Road Brackmills Trading Estate Northampton NN4 7PY Tel: (0800) 626422 Fax: (01604) 667001
  3. 3. The importance of This means that many axis The importance of identifying the allowance appear longer than others for effective cable for reserve stroke the same stroke length. It is management systems Remember to check whether possible to use some of this Do not discount the over travel or stroke reserve stroke reserve and therefore importance of cable is included on your reduce the length of the axis, management systems when mechanical axis. Many depending on the speed and integrating electric drives manufacturers include a load of the application. into an application. distance at each end of the Beware, if this reserve is axis which is not part of the totally used up, it can lead to These issues are often as stroke of the system, but not a dangerous catastrophic important as the all manufacturers do this. failure of the system. of the drive itself. Badly This feature ensures that if a designed and installed cable position is programmed in to management can effect the the controller incorrectly and tuning of a drive, create a the motor hits the end limit very noisy application, lead sensor at speed, the motor to premature failure of the can decelerate down before tubes and cables and hits the physical end of the dangerous for operators. axis. Energy chain systems should be treated as an integral part of the design and not as an add-on once the system has been designed. Ensure your electric drive supplier has a grasp of these issues and ensure their axis mountings are designed for the cable management and energy chain systems. Festo Ltd Caswell Road Brackmills Trading Estate Northampton NN4 7PY Tel: (0800) 626422 Fax: (01604) 667001
  4. 4. What are the differences Ballscrews, which between spindle drives, confusingly are often referred lead screws and to as spindle drives, consist of a ground or rolled spindle ballscrews? and a helical nut which Many people ask what the contains recirculating ball main differences are between bearings. Ballscrews give a spindle drives, lead screws long life and play free, and ballscrews. Much of the accurate positioning. confusion stems from Disadvantage are the higher terminology and market cost and they are not self location. Terminology in the locking, needing a braked USA often varies from that in motor in vertical Western Europe. Lead screws, often called trapezoidal spindles, consist of a trapezoidal thread form and often a polymer nut. They tend to be low cost and offer the benefit of being self locking due to the thread form. Disadvantages are lower life expectancy and a small amount of play. Ballscrew Nigel Dawson is Product Manager for electric drive automation at Festo Festo Ltd Caswell Road Brackmills Trading Estate Northampton NN4 7PY Tel: (0800) 626422 Fax: (01604) 667001