1. When would I need a CMC roller screw driven actuator instead of a ball screw actuator?
Roller screws can handle more loads in smaller footprints, can move the loads faster, and will last much longer than ball screws. In Creative Motion Control’s CPD actuators, the combination of CMC’s roller screws and CMC’s patented thrust bearings (see #5) give the CPD actuators significantly higher force density than anyone else in the industry.
2. When would I need a CMC roller screw driven actuator instead of hydraulics?
Replacing hydraulics with electric actuators requires the same high force density and high-speed capability of the hydraulics. Therefore the only solution is a roller screw actuator. But you get a lot more benefits with a CPD actuator than just force density: the dramatic reduction in maintenance is often reason enough, but on top of that you get higher precision, lower noise, a much simpler changeover to different processes, more flexibility in your moves, and far simpler commissioning. In addition, you remove the risk of hazardous waste spills of hydraulic fluid from leaks which can be extremely expensive and time-consuming. All of those are great, but TCO (total cost of ownership) may be the most exciting. As the cost of energy continues to grow, electric actuators that only need to draw max current when the actuator is exerting max force compared to the constant max draw of the hydraulic power plant often pay for themselves in power savings over the first several years of use.
3. How do I select the right size actuator?
Many times engineers and distributors will size an actuator simply on the basis of the maximum load of the application. This often leads to unhappy customers with actuators that do not last as long as they would like. Selecting the appropriately sized actuator for a given application requires an analysis of the load/stroke profile (the level of load throughout the length of the extent and the return strokes) along with the duty cycle and a minimum life expectancy.
4. What features set the CPD actuators apart from the competition?
CMC’s CPD advantages include:• higher force density (more load in a smaller space)• longer life• ZERO maintenance• unlimited gear reducer/increaser options• the highest static force capabilities in the industry• available customizations• internal anti-rotation• IP67 compliance• 100% MADE IN THE USA by Creative Motion Control
5. Why is CMC’s Grooved Roller Bearing so much better?
The Grooved Roller Bearing (GRB) design was borne of CMC’s roller screw expertise. The GRB is essentially a zero lead roller screw, therefore it benefits from all of the advantages that roller screws have over ball screws: more contact points provide more force in the same physical space (higher force density). This is critical in roller screw actuators because the bearing is the gating component in the drive train — bigger bearings just won’t fit into the space available. Therefore the whole unit’s capabilities max out with the bearing’s capabilities. CMC’s GRBs actually have better force density than the roller screws, so we are able to take full advantage of the roller screw’s high load and life capacities in our CPD actuators.
6. Why would you want CMC’s oil-filled actuator instead of a competitor’s greased actuator?
The quick answer is it enables you to completely avoid maintenance for the life of the actuator. The benefits of that quick answer, however, can be extensive. With grease, the maintenance schedule must be strictly adhered to. Exlar recommends shutting down the machine and removing the actuator to perform periodic maintenance. If the maintenance schedule is not followed, it results in the grease lubrication deteriorating to the point of overheating and resulting in a catastrophic failure of the actuator, and that requires a total replacement.
7. How do I know how big the motor is that I need to do the job?
The CPD catalog has a page titled Motor Selection which provides the basic calculations needed to get you in the right ballpark in terms of torque and power required for your application. Further granularity is required to determine if your specific move(s) can be accomplished with a specific motor and is analyzed using software from the motor manufacturer.
8. What are some typical applications that are a good fit for CMC’s roller screw actuators?
Pressing, crimping, bending, riveting, welding, automation operations, valve and blade control, clamping, stamping, broaching, drilling, positioning… Many of our products are used on application-specific machine tools. Industries include automotive, broaching, thermoforming, injection molding, pressing, defense, mobile equipment, metal/tube bending/cutting/forming, wood processing, simulation, robotic welding/fastening/joining, food processing, oil & gas (including explosion-proof).
9. How do I figure out what the life of the actuator will be?
The basis of the life calculation for a roller screw is fairly straight-forward; it is based on the loads throughout the stroke and the amount of travel the roller screw will handle at those loads. So “life at max load”, a specification often listed in catalogs, is simply the number of inches/mm that a unit can travel at that max load before pitting emerges on the rolling contact surfaces of the roller screw. However, this statistic is relatively meaningless; if you operate at max load, the life of the actuator would be relatively short. Instead, an accurate life expectancy requires a complicated algorithm to be calculated based on the actual loads throughout the stroke and applied to the duty cycle. HOWEVER, it’s important to understand that for an actuator, this calculation needs to be performed using the max continuous load capability of the actuator, NOT the dynamic load capacity of the roller screw. The dynamic load capacity of the roller screw is often highlighted to give the reader the impression that the actuator has more force/life capability than it actually does. We have an Application Worksheet that gives you a template to provide the information we need to make this calculation for you.
10. What is the maintenance schedule for a CMC CPD actuator?
Standard CPD actuators are oil filled and require NO MAINTENANCE for the life of the actuator.
11. If the loads are extreme, can you use two/four CMC actuators and synchronize them?
Our largest actuator can handle 250,000 lbf continuous, so it’s not very common to need more than that. But yes, this approach is used in very high load or extremely repetitive applications requiring long life, or when applying the force on all four corners of a large platen is required for stability. The actuators can be electronically synchronized through the driver software or can be mechanically connected.
12. How can I buy CMC actuators?
If you don’t have a local distributor or rep that has presented you with CMC’s products, you can contact us at firstname.lastname@example.org and we will assist you in either providing the actuator directly or in connecting you to local sales and support.
13. Does CMC sell motors and drives?
No, CMC is focused on providing our customers with the best mechanical solutions we can offer. Motors and drives are generally purchased through distributors local to the customer, but CMC has local partners here in Seattle that can provide that service as well.
14. What are CMC’s lead times?
The standard lead time for a CPD actuator with no customizations is 6-7 weeks. Customizations generally will add from one day to one week.
15. Does CMC purchase any components of their actuators?
Only the basic commodity components; nuts and bolts, seals, oil, etc. All other components are manufactured by CMC in the United States.
16. Can I get a load cell with a CMC actuator?
Yes, with the internal load cell option CMC provides one active load sensor set along with two backup sets to avoid having to open the actuator to service the load cell if for some reason the load cell is not functioning properly.
17. What if I need a custom mount or a custom rod end?
Custom mounts and custom rod ends are no problem; we can always make the mounts or rod ends to your specifications. The cost is generally small and the increased lead time is just a few days.
18. Can I get custom lengths?
Yes. The cost is minimal and the lead time is often not extended.
19. Can you make longer stroke lengths than what is listed in your catalog?
Yes. We will work with you to ensure there are no buckling and/or whirl mode issues, but aside from that, we can make longer units.
20. What if my motor is too big for the space available?
Because the CPD actuators have such high dynamic load ratings, it is not uncommon to want to put a larger than ‘normal’ motor on the unit. In this case, CMC will make a custom, larger motor mount for the selected motor. If the actuator is a parallel configuration, this would include a custom ‘gear tower’ and gear set, but it still less expensive than moving to a larger actuator to handle the larger motor.
21. Can you move the oil reservoir to a different location on the actuator?
Yes, the oil reservoir can be located on any of the four sides of the actuator, and there is some freedom in linear location as well. In almost all cases, the reservoir is not needed if the application is horizontal. And if there is just no way for the reservoir to fit, we can grease the actuator.
22. Can you get a CPD actuator with grease instead of oil?
Yes. Most customers want the oil-filled unit to eliminate maintenance requirements, but in some cases (vacuum environments, certain food processing environments, etc), oil is not an option. In these cases, CMC will grease the unit and provide grease ports for periodic re-greasing.
23. Do CMC actuators backdrive?
Yes, CMC actuators will backdrive. We make the actuators as efficient as possible (generally between 85% and 88%) to reduce the torque and power requirements of the motor to drive them. Customers use a motor brake to avoid backdriving if this is a problem.
24. Are the rated forces available in both directions?
Yes, CPD actuators are designed to handle the same force capabilities in both directions.
25. Why does CMC list a “static load capacity” for their actuators (no one else does that)?
CPD actuators are designed and built to handle the rated static load forces (plus a safety factor), not just the rated continuous dynamic forces. Roller screws are capable of significant static loads, so CMC designs and builds the CPD actuators to take advantage of those capabilities – unlike the competition that cannot handle static loads any greater than their rated continuous load capability (which is why they don’t list a static load specification). This is especially helpful in applications like injection molding where the dynamic forces are minimal but the static or holding forces can be significant. CMC can support these applications with much smaller (and therefore less expensive) actuators.
26. Is the CMC rated continuous load capacity for the entire actuator or just the roller screw?
The max continuous dynamic force specification is for the entire actuator, not just the roller screw.
27. CMC actuators have superior features and performance; are they way more expensive?
No. CMC’s CPD actuators, though more capable, are competitively priced against actuators of the same frame sizes. Often customers use a smaller CPD actuator to do the same job, so they end up being much less expensive.
28. What if I need a smaller lead on the roller screw?
CMC took a different and more flexible approach to enable different speed/torque requirements. Instead of changing the lead of the screw – which is changing the most expensive component of the actuator – CMC supplies different gear configurations to either reduce or increase the speed of the roller screw shaft. If one of the available standard gear ratios do not fit your needs, we can provide custom gear ratios to your specifications.
29. Do you do custom gear ratios?
Yes, see #28.
30. What is backlash?
Backlash is the amount of play or ‘lash’ that exists in a mechanical assembly of moving parts. As the actuator reverses direction, there is some very small amount of delay in the reaction of the actuator before it begins moving in the other direction. That amount of play is called backlash. The amount of backlash in CPD actuators is between .002” and .003” depending on the size. The key is that this backlash is extremely repeatable. After reversing directions, the CPD actuator will move to the same spot to within .0008” every stroke for the life of the actuator.
31. What is the accuracy of CPD actuators?
Accuracy is just another term for repeatability. See #30.
32. What is lead error, and why doesn’t CMC provide a lead error specification?
Lead error is a manufacturing specification for screws; ball screws, lead screws and roller screws. As you can see in our roller screw catalog, CMC roller screws are built to the industry standard G5 accuracy which means the error in the lead of the screw shaft is within .0023mm/300mm. This specification, however, is just a piece of the ‘accuracy’ of an actuator, so is not relevant to the reader. The accuracy, or repeatability, of an actuator, is the key specification to determine the error in the travel of the unit (see#30). This takes into account the roller screw, bearing, gears/belts, etc.