ALLOWABLE LOAD

Load and Moment:

Figure 1-1 Load and Moment

A load may be exerted to a linear system as depicted in Figure 1-1. In addition, a moment may be applied to a slide guide. Each type of load addressed by NB is described as follows.

rated loads C and Coload direction of momentpitch yaw roll Table 1-1 Minimum Static Safety Factor

Basic Static Load Rating(compliant with ISO14728-2

) and Allowable Static Moment:

Under excess or impact load conditions applied to a linear system while it is stationary or moving slowly, a permanent deformation occurs on either the rolling surface or the rolling elements. When this deformation exceeds a predictable level, it becomes a source of vibration and acoustic noise during operation and will also result in rough motion and shortens life. To prevent this permanent deformation and deterioration in movement accuracy, a basic static load rating (Co) is given as an allowable load. This basic static load rating is defined as the static load that results in the maximum allowable stress at the center of the contact surface between the rolling elements and the rolling surface. The sum of the permanent deformation of the rolling elements and that of the rolling surface is 1/10,000 the diameter of the rolling elements. In linear systems, a moment may also be present when applied in addition to the static load. The allowable static moment is defined by M

, M

, and M

, which are illustrated in Figure 1-1.

*1: This does not apply to some products.

Allowable Load and Static Safety Factor:

The basic static load rating and allowable static moment define the maximum static load in each direction. These maximum static loads are not necessarily applicable depending on the operating conditions, the mounting accuracy, and the required motion accuracy. Therefore, an allowable load with a safety factor that covers these factors must be obtained. In general, the minimum static safety factor is based on the values as listed in Table 1-1.Allowable load

operating conditions static safety factor normal 1 2 smooth motion required 2 4 vibration/impact loading 3 5

P

max

. Co/fs (1)

Allowable moment

M

max

. (M

,M

)/fs (2)

fs : static safety factor Co : basic static load rating(N)Pmax. : allowable load(N) M P ,M R ,M Y : allowable static moment(N m)Mmax. : allowable moment(N m)

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