THK Linear Motion Guide Features

As a result, the following features are achieved.

Large Permissible Load and High Rigidity

Large Permissible Load

Comparison between THK LM Guide and the Linear Bushing

THK LM Guide has raceway grooves with a radius almost equal to the ball radius, which is significantly different from the linear bushing. As shown in Fig.1 , which compares size between the LM Guide and the linear bushing with similar basic dynamic load ratings, the LM Guide is much smaller than the linear bushing, indicating that the LM Guide allows a significantly compact design.

The reason for this space saving is the greater difference in permissible load between the R-groove contact structure and the surface contact structure. The R-groove contact structure (radius: 52% of the ball radius) can bear a load per ball 13 times greater than the surface contact structure. Since service life is proportional to the cube of the permissible load, this increased ball-bearing load translates into a service life that is approximately 2,200 longer than the linear bushing.

Load Capacity per Ball

	R-groove (p)	Flat surface (P1)	P/P1
3.175 (1/8")	0.9 kN	0.07 kN	13
4.763 (3/16")	2.03 kN	0.16 kN	13
6.35 (1/4")	3.61 kN	0.28 kN	13
7.938 (5/16")	5.64 kN	0.44 kN	13
11.906 (15/32")	12.68 kN	0.98 kN	13

High Rigidity

THK LM Guide is capable of bearing vertical and horizontal loads. Additionally, due to the circular-arc groove design, it is capable of carrying a preload as necessary to increase its rigidity.

When compared with a feed screw shaft system and a spindle in rigidity, the guide surface using an LM Guide has higher rigidity.

High Precision of Motion

Small lost motion

THK LM Guide is provided with an ideal rolling mechanism. Therefore, the difference between dynamic and static friction is minimal and lost motion hardly occurs.

High running accuracy

Use of THK LM Guide allows you to achieve high running accuracy.

High accuracy maintained over a long period

As THK LM Guide employs an ideal rolling mechanism, wear is negligible and high precision is maintained for long periods of time. As shown in Fig below, when THK LM Guide operates under both a preload and a normal load, more than 90% of the preload remains even after running 2,000 km.

Condition

Conditions
Model No. : HSR65LA3SSC0 + 2565LP-Ⅱ
Radial clearance: C0 (preload: 15.7 kN)
Stroke : 1,050mm
Speed: 15 m/min (stops 5 sec at both ends)
Acceleration/decelelation time in rapid motion: 300 ms (acceleration:  = 0.833 m/s 2 )
Mass : 6000kg
Drive : Ball Screws
Lubrication : Lithium soap-based grease No. 2 (greased every 100 km)

Accuracy Averaging Effect by Absorbing Mounting Surface Error

THK LM Guide contains highly spherical balls and has a constrained structure with no clearance. In addition, it uses LM rails in parallel on multiple axes to form a guide system with multiple-axis configuration. Thus, THK LM Guide is capable of absorbing misalignment in straightness, flatness or parallelism that would occur in the machining of the base to which the LM Guide is to be mounted or in the installation of the LM Guide by averaging these errors.

The magnitude of the averaging effect varies according to the length or size of the misalignment, the preload applied on the LM Guide and the number of axes in the multiple-axis configuration. When misalignment is given to one of the LM rails of the table as shown in Fig below, the magnitude of misalignment and the actual dynamic accuracy of the table (straightness in the horizontal direction) are as shown in Fig below.

By applying such characteristics obtained with the averaging effect, you can easily establish a guide system with high precision of motion.

Even on a roughly milled mounting surface, the LM Guide drastically increases running accuracy of the top face of the table.

Easy Maintenance

Unlike with sliding guides, THK LM Guide does not incur abnormal wear. As a result, sliding surfaces do not need to be reconditioned, and precision needs not be altered. Regarding lubrication, sliding guides require forced circulation of a large amount of lubricant so as to maintain an oil fi lm on the sliding surfaces, whereas the LM Guide only needs periodical replenishing of a small amount of grease or lubricant. Maintenance is that simple. This also helps keep the work environment clean.

Substantial Energy Savings

THK LM Guide has a substantial energy saving effect.

Low Total Cost

Compared with a sliding guide, the LM Guide is easier to assemble and does not require highly skilled technicians to perform the adjustment work. Thus, the assembly man-hours for the LM Guide are reduced, and machines and systems incorporating the LM Guide can be produced at lower cost. The fi gure below shows an example of difference in the procedure of assembling a machining center between using siding guides and using LM Guides.

Normally, with a sliding guide, the surface on which the guide is installed must be given a very smooth fi nish by grinding. However, the LM Guide can offer high precision even if the surface is milled or planed. Using the LM Guide thus cuts down on machining man-hours and lowers machining costs as a whole.

Ideal Four Raceway, Circular-Arc Groove, Two-Point Contact Structure

THK LM Guide has a self-adjusting capability that competitors’ products do not have. This feature is achieved with an ideal four raceway, circular-arc groove, two-point contact structure.

Superb Error-Absorbing Capability with the DF Design

Since the LM Guide has a contact structure similar to the front-to-front mount of angular ball bearings, it has superb self-adjusting capability.

An THK LM ball guide mounted on a plane receives a moment (M) due to an error in flatness or in level or a deflection of the table. Therefore, it is essential for the guide to have self-adjusting capability.