Caged Ball LM Guide Actuator Model SKR

The Model SKR Caged Ball LM Guide Actuator is a compact actuator that has an inner block consisting of LM blocks and a ball screw nut integrated inside a U-shaped outer rail.
In addition, this model achieves high-speed operation, lower noise, and longer-term maintenance-free operation by using ball cages in the LM Guide units and the ball screw unit. (A ball cage is used only for the LM Guide section of Models SKR20 and SKR26, and the ball screws are fitted with QZ Lubricators.)

Precautions on Use

Types

Highlight feature tags

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Long-term maintenance free
High rigidity
High accuracy
High speed
Space saving
4-way equal load

Features

Structure and Features

Caged Ball LM Guide Actuator model SKR is a compact actuator that has a inner block consisting of LM blocks and a ball screw nut integrated inside a U-shaped outer rail. In addition, this model achieves high speed operation, lower noise and longer-term maintenance-free operation by using ball cages in the LM Guide units and the Ball Screw unit. (A ball cage is used only for the LM guide section of models SKR20 and SKR26 and the ball screws are fitted with QZ lubricators.)

4-way Equal Load

Each row of balls is arranged at a contact angle of 45° so that the rated load on the inner block is uniform under loads applied to the inner block in the four directions (radial, reverse radial and lateral directions). As a result, model SKR can be used in any mounting orientation.

High Rigidity

Use of an outer rail with a U-shaped cross section increases the rigidity with respect to moment and torsion.

Table1 Cross-sectional Characteristics of the Outer Rail

Model No.	l_X[mm⁴]	l_Y[mm⁴]	Mass[kg/m]
SKR20	6.0×10³	6.14×10⁴	2.6
SKR26	1.66×10⁴	1.48×10⁵	3.9
SKR33	5.35×10⁴	3.52×10⁵	6.1
SKR46	2.05×10⁵	1.45×10⁶	12.6
SKR55	2.07×10⁵	2.09×10⁶	13.2
SKR65	4.51×10⁵	5.73×10⁶	22.1

l_X =geometrical moment of inertia around X axis
l_Y =geometrical moment of inertia around Y axis

High Accuracy

Since the linear guide section consists of 4 rows of circular-arc grooves that enable balls to smoothly move even under a preload, a highly rigid guide with no clearance is achieved. Additionally, variation in frictional resistance caused by load fluctuation is minimized, allowing the system to follow highly accurate feed.

Space Saving

Due to an integral structure where LM Guide units are placed on both side faces of the inner block and a Ball Screw unit is placed in the center of the inner block, a highly rigid and highly accurate actuator with a minimal space is achieved.

Caged Ball Technology

High Speed

Model SKR supports a latest high-rotation servomotor (6,000 min^-1) by using a ball cage and is capable of operating at higher speed than the full-ball type model KR. Models SKR33/55/65 are available in more leads variations to achieve higher speed operation and high leads are available which was not feasible with the model KR.

Model No.	Lead
Model No.	SKR	KR
33	6,10,20	6,10
55	20,30,40	20
65	20,25,30,50	25

High Lubricity

Model SKR uses ball cages to eliminate friction between balls and significantly improve torque characteristics. As a result, the torque fluctuation is reduced and superb lubricity is achieved.

Item	Description
Shaft diameter/lead	ø 13/10mm
Shaft rotation speed	60min^-1

Low Noise, Acceptable Running Sound

In model SKR, the use of a ball cage in the LM Guide section and Ball Screw section (excluding models SKR20/26) has eliminated collision noise between the balls. As a result, low noise and acceptable running sound are achieved.

Long-term Maintenance-free Operation

With model SKR, the ball cage effect helps increase grease retention and achieve long-term maintenance-free operation.

Long service life—3 times

With model SKR, both the LM Guide unit and the Ball Screw unit have larger basic dynamic load ratings than the full-ball type model KR, and therefore a longer service lives are achieved. The rated service life is calculated from the following equation.

LM Guide unit L₁₀=(C/P)³×50 L₁₀: Nominal life C : Basic dynamic load rating P : Applied load	(km) (N) (N)

LM Guide unit

L₁₀=(C/P)³×50

L₁₀: Nominal life

C : Basic dynamic load rating

P : Applied load

(km)

(N)

Ball screw unit

L₁₀=(Ca/Fa)³×10⁶

L₁₀: Nominal life

Ca : Basic dynamic load rating

Fa : Applied axial load

(rev)

(N)

As indicated in the equation above, the greater the basic dynamic load rating, the longer the service life of both the LM Guide unit and the Ball Screw unit.

Table2 Comparison of Basic Dynamic Load Rating between Model SKR and Model KR

Unit: N

Basic dynamic load rating		SKR 20	KR 20	SKR 26	KR 26	SKR 33	KR 33	SKR 46	KR 46	SKR 55	KR 55	SKR 65	KR 65
LM Guide unit C	Long type block	6010	3590	13000	7240	17000	11600	39500	27400	55400	38100	74400	50900
LM Guide unit C	Short type block	-	-	-	-	11300	4900	28400	14000	-	-	-	-
Ball screw unit Ca		660	660	2350	2350	2700	1760	4240	3040	10900	3620	12000	5680

Note) On the SKR20/26, only the LM guide section features a ball cage.

Seal

Model SKR is equipped with end seals and side seals for dust prevention as standard.

Table3 shows the rolling resistance and seal resistance per inner block (guide section).

Table3 Maximum Resistance Value

Unit: N

Model No.	Rolling resistance value	Seal resistance value	Total
SKR20	4.0	0.8	4.8
SKR26	4.5	1.2	5.7
SKR33	3.0	1.7	4.7
SKR46	6.0	2.1	8.1
SKR55	14.0	3.8	17.8
SKR65	20.0	4.1	24.1