good day (daytime greeting)"Motorized Drive Selection Factors and Practices."It is a note about.
The type of drive selected for a machine takes into account the customer's requirements, but as a precondition, it is necessary to select a drive system that can satisfy the quality requirements of the machine.
The best drive method will vary depending on how you handle the object to be driven, such as pushing, carrying, etc. Here we note the characteristics of each drive system and some in-depth information to help you make those choices smoothly.
Please refer to this section as the choices here are very important, especially in the early stages of design.
Drive method using motors
Ball screw drive
The first thing that comes to mind is the mechanical structure.Motor + ball screw drive It is This mechanism converts the rotational motion of a motor into linear motion and is used in many machines.
This mechanism is a drive method that has less friction on the structure itself and can achieve high control accuracy (positional accuracy).For ball screws,Rolling Ball Screws and Precision Ball ScrewsThere are two types of "stop systems" and they are selected according to the degree of demand for the stop system (repetitive positioning accuracy) required for the machine.
Ball screws are,Converting rotational motion into linear motion by applying the mechanism of a screw and nut (a ball takes the place of the screw thread)The ball screw has the advantage of being able to provide a large thrust force because it has a built-in ball circulation system and grease supply system. In addition, each ball screw manufacturer has its own features, such as the built-in ball circulation system and grease supply system.
There is some backlash (gap between the screw and nut) in the structure, but there is also a pressurized specification that absorbs the backlash.Drive method for high efficiency, high thrust, and long lifeIt can be said that
One disadvantage in use is that the cost is inevitably higher than other drive systems, but this should be considered a reasonable cost for the required quality.However, this drive is not perfect,Not suitable for high speed exercise or long distancesIt is.
The expression "high-speed motion" is ambiguous, but what it means is that a ball screw converts motor rotation into linear motion, so, for example, a ball screw with a small lead (a ball screw with a fine thread) is necessary to obtain a high thrust, but this requires a higher motor rotation speed. The second is that the operating speed is limited by the motor's limitations.
Next, the ball screw itself also has a critical speed limit. This value is specific to the product used.
As for long distance, this is also ambiguous, so to be more specific, long distance = long threads, which may cause buckling due to axial load, and assembly accuracy will be more strict because the fulcrum distance will be greater, so more design know-how, such as fixing methods, will be required for long distance.
In summary, ball screw drives areIt is a drive method for high efficiency, high thrust, and long life, but it is not perfect because there will be cases where it cannot be used due to high speed motion or drive distance.I think we should be aware of this.
Rack & pinion drive
This mechanism isA mechanism in which a gear (pinion) rolls on a rack in linear motionIt is.
The main advantage of this drive is that it is capable of long-distance motion and has a structure that is easy to disassemble and disassemble. The module determines the capability of the rack and pinion.A module is defined as the ratio of the pitch diameter circle (the reference circle of the gear) to the number of teeth. TheIf the module has the same gears and racks, gears with different diameters will mesh correctly.
This mechanism has the advantage of allowing the user to choose the drive structure, since the rack can be fixed and the motor with gears can move, or the motor can be fixed and the rack can move. However, if the motor movesCable bearCare is also taken to protect wiring such as
The disadvantage of using this type of gear is that it is not suitable for precision control because of the backlash (gap between the teeth). Some designers use gears to eliminate backlash, but this is not common practice. If the stress on the tooth surface exceeds the allowable value, the surface may wear or delaminate.Design and understanding of tooth surface strength is importantIt is.
And finally, there is noise. Rack and pinions produce noise without proper lubrication.
Looking at the rack and pinion structure overall, it is a very good structure because it is suitable for long distances and has a very simple structure (resulting in low cost), but when considering the precision of the gear mounting parts, the effects and protection of gear lubrication and lubricant (grease) dripping, and cable protection of the drive objectUnsurprisingly difficult structure for the uninitiatedwill be.
Therefore, it is a good idea to employ it in a structure where errors are tolerated.
andRack and pinions will also require individual stoppers in case of runaway.Overrun sensorKnowledge of such things asThe first time the company has been in the market for a new product, it has become
*This overrun is true for other drives as well, but other drives have structures in front and behind that act as stoppers at worst, meaning that in rack and pinion, particular attention to stoppers is necessary.
Timing belt drive
Timing belt drive isMechanism similar to conveyor imagebecomes
The belt is used to transmit power, resulting in low noise, low vibration, and smooth operation. Maintenance-free: No lubrication is required, and the performance is backlash-free. (by adjusting the tension).
In other words,If the drive is lightweight and a situation can be created where the belt does not stretch or contract, high-precision operation is possible over long distances.The first two are the following.In addition, the tendency is toLightweight components mean low load on the motor.It is.
However, there is a disadvantage, or rather a caveat,Be aware of the possibility of belt stretching and the low durability unlike chains, etc.It is. It is not suitable for high-load (e.g., rapid acceleration of high-mass objects) transport.
Therefore,Timing belt drive is suited for long-distance transport operations of relatively lightweight itemsIt can be said that
Chain Drive
Next is the chain drive. I don't think this needs explanation, but I will summarize the main points.
The chains are made of metal, except for some parts, for durability and high transmission capacity. It is also characterized by its ability to operate in some outdoor environments, such as weather-resistant environments.Motors that drive chains are basically used for applications that rotate in one direction, such as induction motors, but I believe that chain drives are only used for loading and transporting to one direction.
Although a little unusual, large lifting equipment can be lifted using chains instead of loops.
The disadvantage is that it is sometimes accompanied by loud vibration and noise. In the case of a chain drive, the chain is basically driven by rubbing the chain guide, so care must be taken in designing the area around the chain, such as by hardening or using a guide made of low-friction resin for the parts that rub against it.
Cam Drive
Next comes the drive using cams. Cams are used less and less in modern machines, though,Cam drive repeats a certain motion (cycle) depending on its geometryYou can do this.
Although the system is capable of high-precision motion control, it is subject to friction, so if the system is designed to have high durability and a long service life, it can be operated with fewer failures.
One thing to keep in mind when dealing with cams is that while they are capable of a wide variety of movements, they are also complex in design. Once a cam is set up, it is not easy to change the design because of the interlocking units in the surrounding area.
Nevertheless, it is a convenient mechanism that can also be used independently.
linkage
linkageis a must for anyone who loves mechas.
The useful thing about the link is that it can repeat a certain motion (cycle) just like a cam.
The design of the linkage part of a linkage mechanism is a difficult aspect. Since a linkage is a combination of objects that move mainly in the rotational direction, it basically cannot withstand loads from the lateral direction, so it is necessary to consider loads in the rotational direction (radial load) and thrust direction for a linkage mechanism that is set directly horizontal.
And, as with cams, once the linkage is set, it is not easy to change the design because of the interlocking units around the linkage. It is difficult to determine where to place the adjustment mechanism.
Finally.
Finally, I would like to note what I think about the recent situation of production facilities.
Over the past few years, we have seen an increase in the purchase of actuators with built-in features rather than conventional mechanical mechanisms.
The most popular type is IAI's ROBO CYLINDER. The RoboCylinder lineup is based on the "motor + ball screw" structure described above, but there are also long types with belt specifications at the limit of the structure.
IAI's basic model comes with a motor, but SMC, CKD, THK, and others offer a choice of attachments so that each manufacturer's motor can be installed.These actuators are useful, though,I think we can use it because we understand the characteristics of the old driving method.
For example, if you try to transport an object with this type of actuator, you basically have to design it so that the center of gravity is directly above the object, otherwise the life of the actuator will be shortened. On the other hand, if you put a motor and ball screw between the LM guides, it may be too much.
In actual design, what you want to do comes first, and how to do it comes second.
- What do you want to do: I want to carry a 100 kg piece of steel to 2 m away in about 3 seconds.
- How can we do that: I want to put it on and transport it (or maybe I should put it on).
At this point, the load (required driving force) can be roughly calculated, and the next step is to select a driving method that is likely to satisfy the load.
The drive to transport that 100 kg object 2 m in 3 seconds can be anything (in fact, ball screws are often retired here), but the size and the layout that the machine installation environment allows are additional factors here.
- Workpiece shape：Steel plate
- Installation environment: Close to outdoor environment
For example, if the conditions were such that a chain or rack-and-pinion construction that is easy to extend over long distances and seems to be strong in the outdoor environment would be good, wouldn't it? This would be the case.
What if it were all the other way around?
- What do you want to do: I want to carry 1 kg of a lump of resin to 1 meter away in about 3 seconds.
- How can we do that: I want to put it on and transport it (or maybe I should put it on).
- Workpiece Shape：Square
- Installation environment: Indoor
For example, in this situation, a ball screw is a good drive method, or you can purchase an inexpensive belt-type actuator that is advantageous for transporting lightweight materials.
If the drive distance is even shorter than this, a link or cam mechanism is another candidate.
Ultimately, the choice of drive method isThere may be one answer, but even a near-pin answer may be the right answer in that case.This can be said to be the case.
I have designed light to heavy, small to large, indoor or outdoor, in many different environments, after all,The key to determining the drive method is how much information can be gathered to meet the selection criteria, and beyond that, the part about whether the capacity is sufficient or not is influenced by the designer's computational ability.I think that is why.
Up to that calculation, I think anyone can do it, or even if they don't know the calculation, they can do it if they study it, so I don't think it is difficult. It's just that,Designers who have experience with all kinds of drive methods have experience, so even with the commonly selected drive method, they can use their experience to say, "In this case, you should choose B over A," or "In this case, you should choose B over A," or "In this case, you should choose B over A."Design the structure to minimize breakdowns and add an adjustment mechanism" and so on will become the know-how.I know, right?
What I think is important is to stop thinking in terms of commercially available actuators, but rather to assess the situation, select the best drive method, and design it to use it correctly.
And I think those are the designer skills that are needed. I also think that these are the designer skills that are needed.
I am of the high-mix low-volume generation, not the mass production era, so my experience with cam structures is actually quite limited.That's what I think about,A sense of crisis in a sense that there will probably be some mechanisms in the future that will not be learned in practice.There are
If you are wondering what the actual drive is, we have introduced it in the past.Refer to the bookI hope to have them do so.
That's it.