Roh’lix linear actuator by Zero-Max/Helland, Minneapolis, can have rated thrust as high as 200 lb, linear speed to 70 ips, and shaft speed to 1,600 rpm. Lead can be as small as 0.025 in./rev; as large as 60-in./rev. Three ball bearings at each end of a 2-piece aluminum block and at an angle to the rotating driveshaft convert shaft rotary motion to block linear motion. The two block halves are assembled over the driveshaft so the shaft and its bearings need not be removed for installation.

All right, so it’s not quite so simple as that. Still, it works and several suppliers offer such units for a variety of applications. By adding means to adjust the size of the angle between shaft and roller axes, or to reverse the angle (and thus, linear-motion direction), you obviate the need to adjust motor speed or direction — the device becomes more versatile. Below are some of the best and worst situations for threadless mechanical linear actuators.

Where to; where not to

Wherever you need rapid, repetitive, oscillating linear motion, a threadless mechanical linear actuator is worth considering.

Best spots. Typical applications where such devices are already at work include:
• Spooling.
• Slitting.
• Spraying.
• Feeding.
• Stretch-wrapping.
• General packaging.
• Indexing and pick and place.
• Back gaging in metal bending.
• Door operating.

You can get thrust to 150 lb and linear speed to 8 ips with Magline linear actuators by Magnetic Corp., Olney, Ill. Move the system with on-board motor as in the illustration, or move the shaft, or hold motor system and shaft linearly and run one or more roller heads. Applications are numerous. Imagine operating a group of roller heads, each head at different speed. Now, off of the same driveshaft, simultaneously run a second group in mirror image to the first. Application: telescoping doors.

Take care. Conversely, some applications don’t lend themselves well to threadless mechanical linear actuators unless you take special precautions:

• Heavy direct or side load situations on the driveshaft itself are not good. You can get systems with special linear-bearing options to take the load off the shaft.

• In general, look with caution at unclean environments. Dirt picked up on an exposed driveshaft can transfer to the roller system, causing damage like you might expect in any contaminated rolling-element bearing system. Special boots or bellows may help.

• Where positive drive is needed, that is, where you need high precision and repeatability, consider alternatives such as ball screws or precision lead screws. You might be able to use a threadless linear actuator by adding servo control with positive feedback and motor control, but that complexity could negate the system’s basic simplicity.

Application hints

Life. Threadless mechanical linear actuators typically are rated much like ball screws and linear rolling-element bearings: for life in inches of linear travel. In general, manufacturers size units and recommend selection procedures that offer life spans in millions of inches. Unless you have specific life in mind, choose a system that can provide 1 million to 100 million in. of travel.

Factors that can reduce normal life include:

• Thrust. Generally, thrust settings below catalog rating help extend life. If your application’s thrust exceeds a catalog rating, try the next higher catalog rating.

• Lead. Bearings support the driveshaft and the skewed rollers. The fewer the number of turns those bearings make for a given travel, the longer the system life. Therefore, higher leads promote longer life.

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