Kinetic Solutions Intl, Inc. shows a prototype Simplex Aerospace Water Cannon driven by an Exlar GSX actuator and SLG motor.
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What is the best approach for your electrical system?
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Ever wondered which actuators are the best option for your application?
This digestable, two-page article supplies frequently asked questions including:
- Reasons to choose electric actuators over hydraulic
- Challenges replacing a hydraulic system
- What industries are using electric actuators to their benefit
- And more
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Are you hearing unusual noises or seeing blackened grease leaking out of your pulley housings resulting in unplanned machine downtime? If you are, you’re not alone. Your actuator may be degrading due to a phenomenon known as electrical discharge (ED).
Stray electrical voltages are traveling from motor shafts through couplings, pulleys, bearings, and housings in a search for ground. Since ball bearings are rolling contacts with lubricant between surfaces, the voltage arcs the gap and causes material erosion, lubricant failure, heat, and ultimately premature bearing failure.
This damage can reduce the life of bearings that should last 6 to 10 years to as little as 2 to 6 months. Your root cause investigation should focus on the motor grounding system as voltage discharges as low as 3.2 volts will cause current discharges across a ball bearing and raceway lubricant gap.
How it works:
Electrical Discharge Machining, sometimes called “spark machining” is a common manufacturing process where material removal is done by triggering a rapidly recurring current discharge between two electrodes separated by a dielectric liquid and subjected to an electrical voltage. One of the electrodes is the part being machined and the other is the “tool” electrode, typically a wire or carbon shape.
The gap between each electrode is precisely controlled and the dielectric liquid fills this gap. As voltage is applied and increased, the intensity of the electrical field in the gap rises and becomes stronger than the dielectric liquid, allowing current to flow or arc across the gap. As a result, material is removed from each electrode and carried away by the dielectric fluid. Performing this arcing at a high frequency results in an efficient erosion machining process that is very good for hardened materials.
Whereas EDM is a practical manufacturing process, it is not desirable in Motion Control systems and applications.
How do you recognize Electrical Discharge?
At first, the continuous arcing will start pitting the bearing raceways and reduce the ball diameter. Ball retainers will also start eroding and break apart. The heat builds due to arcing and friction causing the grease lubrication to breakdown and become contaminated with metal particulate. Blackened grease may leak out of the bearing and be visible on the pulley housing and pulley shaft.
As the bearing degrades and becomes unlubricated, heat and friction build causing metal to metal contact noise. If the actuator drive shaft is decoupled from the motor, you may feel a roughness or bumpiness when rotating the drive shaft. The electrical discharge continues and works its way to all the bearings in the actuator as these are the points of arcing.
As the bearings degrade (balls, retainer cage and polymer seals disappear) and become non-functional the actuator will begin running erratic and make significant noise. In a fully catastrophic case there are no bearings remaining and the pulley is unsupported, the actuator timing will be compromised and other parts of the machine system will be affected.
The shaft-side bearing (left) shows no seal, blackened lubricant and damaged ball cage. The pulley housing and bearing (right) show no visible damage but the bearing rotates with a rough feel indicating Stage 1 damage.
Determining if your actuator has been damaged by ED:
- Measure actuator pulley housings and shafts for a voltage using an Oscilloscope or an Electrical Discharge Pen TKED1 made by SKF. Presence of voltage is a good indicator that ED is contributing to the failure.
- Check all drive system ground connections and cables for proper ground bonding and shielding. If inconsistencies are found, correct and recheck for voltages.
- Measure temperatures of the motor, adaptor and pulley housings for excess heat generation. Hot spots may indicate failure point.
- Replace noisy drive or idler pulley assemblies. Record change dates and monitor the performance over time. It is quite rare for a pulley assembly to fail within 6 months of installation
Hello Automation, Goodbye Manual Palletizing
Palletizer machines have become an essential part of automation, replacing human error and injury in manufacturing with efficiency and speed. In addition to such benefits, palletizers can handle environments that would otherwise be injurious to workers. Instead of requiring the hire of more laborers to do this work, many companies have adopted palletizers into their workplace environments in order to get the job done more quickly, effectively and safely.
The Exlar® FT Series actuators combined with a parallel motor mounting configuration use a polymer reinforced belt drive system. The drive train does not require any lubrication and any oil or dirt contamination within the belt drive system will decrease belt effectiveness and life. The belt and pulley system should be inspected periodically for excessive wear and proper tensioning.
Do not remove the belt cover while the actuator is operating. Always remove power from the attached motor before removing the belt cover to service any component of the drive train (i.e. belts, pulleys, bushings, inline couplings, gears, etc). Failure to do so can result in damage to the actuator or cause serious injury to the operator.
The following picture is only an example of a typical belt and pulley drive train in an FT Series actuator.
These belt drives do not require as much tension as other belt drives that depend on friction to transmit the load. The installation procedure should begin by installing the belt with a snug fit, neither too tight nor too loose. Now, measure the belt span, (t), as shown in the picture above. With one pulley free to rotate, use a spring scale to apply a perpendicular force to the center of the belt width at the mid-point of the belt span. For belts wider than 2”, it is suggested that a strip of keystock, or something similar be placed across the belt under the point of force to prevent distortion. Measure the deflection of the belt at the mid-point. While applying the correct force, there should be 1/64” of deflection for each inch of belt span. For example, the total deflection for a 32” belt span is 32”*1/64” = ½”. The appropriate amount of force for each belt is shown on the customer approval drawing, or you may contact our application engineer team for assistance.