A new generation of disk couplings
|Part Number||Slip Torque||Max. Bore Diameter
|Max. Rotational Frequency
|Moment of |
|Max. Axial |
＊1： Correction of rated torque due to load fluctuation is not required.
The shaft's slip torque may be smaller than the coupling's rated torque depending on the shaft bore. XHW-C＊2： These are values with max. bore diameter.
|Part Number||Standard Bore Diameter D1|
|Part Number||Standard Bore Diameter D2 (Inertial Rotor Side)|
● All products are provided with hex socket head cap screw.
● Recommended tolerance for shaft diameters is h6 and h7.
● Bore and keyway modifications are available on request for D1 only. Please take advantage of our modification services.
● In case of mounting on D-cut shaft, be careful about the position of the D-cut surface of the shaft.
Slip torqueAs in the table below, the clamping type XGHW-C has different slip torque according to the bore diameter. Take care during selection.
|Outside Diameter||Bore Diameter (mm)|
Clamping Type XGHW-CXGHW-C
|Disk Fixing Bolt||SCM435
Ferrosoferric Oxide Film (Black)
|Hex Socket Head Cap Screw||SCM435
Ferrosoferric Oxide Film (Black)
Electroless Nickel Plating
- Recommended Applicable Motor
|High Torsional Stiffness||◎|
|Vibration Absorption Characteristics||◎|
|Allowable Operating Temperature||-10°C to 60°C|
- Flexible couplings with vibration absorption function added to high rigidity couplings.
- A structure with both high rigidity and vibration absorption. The individual dynamic vibration absorber＊1 is separate from the inertial rotor and elastic body in order to achieve vibration absorption.
＊1： The mechanism for suppressing resonant vibration phenomena is achieved by connecting the dynamic vibration absorber to the auxiliary inertial body via the elastic body.
- Does not use resin elastic materials for the rotation transmission system from the motor shaft hub to the driven shaft hub, for high rigidity.
- Achieves high positioning accuracy under high loads, in addition to high servomotor gain.
ApplicationActuator / Surface-mount machine / High precision XY stage / Index table
Precautions for UseWhen installing, be careful not to apply excessive torque, loads or forces to the inertial body. Doing so may result in the inertial body detaching.
Selection Based on Shaft Diameter and Rated TorqueThe area bounded by the shaft diameter and rated torque indicates the selection size.
Selection ExampleIn case of selected parameters of shaft diameter of φ14 and load torque of 3 N•m, the selected size is XGHW-41C.
Selection Based on the Rated Output of the Servomotor
|Servomotor Specifications＊1||Selection Size|
|Diameter of Motor Shaft
|Instantaneous Max. Torque
Gain and Stabilization Time of ServomotorThis shows how the servomotor gain movement follows the command.
Increasing the gain helps to reduce stabilization time, but increasing it too far causes hunting, making servomotor control impossible.
Increasing the gain while suppressing hunting requires fine adjustment of the servomotor parameters.
However, when a servomotor is combined with a coupling with a metal disk type in the elastic segment, raising the gain tends to cause hunting, making it difficult to resolve the problem by fine adjustments to parameters.
When hunting occurs, it is generally recommended to change to a coupling with higher rigidity to increase the rigidity of the rotating system.
However, in reality, it may not be effective to increase the rigidity of the entire rotating system including the ball screw simply by increasing coupling rigidity.
The Vibration-Absorption Capable Disk TypeThe vibration-absorption capable disk type XGHW-C has a dynamic vibration absorber on the high rigidity disk. It enables vibration absorption and use of higher gain levels when compared to regular disk types, thereby also allowing a shorter stabilization time. The vibration absorption function reduces the amount of parameter adjustment work, and lowers the time required to find optimal parameters.
Why can gain be increased even further with the vibration-absorption capable disk type XGHW-C when compared with the disk type XHW-C?The Bode plot clearly illustrates why XGHW-C can increase servomotor gain beyond the capacity of disk types XHW-C.
The width of the gain relative to 0 dB when the phase delay on the Bode plot is -180° is called the gain margin and the phase width relative to the frequency intersecting at 180° is called the phase margin.
General guidelines for servo systems call for setting the gain margin between 10 and 20 dB and the phase margin between 40° and 60°, but as the servomotor gain is increased, the gain margin decreases. When the gain margin falls below 10 dB, hunting tends to occur.
A comparison of the XGHW-C and XHW-C limit gain (upper limit of the gain in which coupling can be used without hunting) shows not only that XGHW-C features a larger gain margin, but that in fact the gain margin is over 10 dB. This is why the servomotor gain is greater in XGHW-C compared to XHW-C.
Gain margin at the disk type limit gain
Comparison of The Vibration-Absorption Capable Disk Type and Disk Type
In tests using servomotors and actuators, the following information is confirmed.
- Stabilization Time
Increasing the gain enables the stabilization time to be shortened, and the gain can be set especially high with the vibration-absorption capable disk type when compared to the disk type.
- Positioning Accuracy/Repeated Positioning Accuracy
No differences attributable to factors such as gain or coupling were observed.
Increasing the gain increases the overshoot, and the same gain resulted in no difference in the overshoot.
The vibration-absorption capable disk type allows higher gain to be set than the disk type, enabling shorter stabilization time. The positioning accuracy, repetition positioning accuracy and overshoot did not differ due to coupling.
As a result, it was confirmed that the vibration-absorption capable disk type is effective for shortening the cycle time of devices and equipment.
Actuator： KR30H Manufactured by THK (Co., Ltd.)
＊ Ball screw lead 10 mm
Servomotor: HG-KR13 Manufactured by Mitsubishi Electric Corporation
Motor revolution: 3000 min-1
Acceleration/deceleration time: 50 ms
Workpiece load: 3.0 kg
Ratio of moment of inertia of load: 2.3
Test OperationNormal rotation (1 rev) → Stop (500 ms) → Reverse rotation (1 rev)
Test MethodA displacement sensor is used to measure work movement, travel distance and stabilization time.
- Measurement of Stabilization Time, Positioning Accuracy and Overshoot
|Gain＊1||The Vibration-Absorption Capable Disk Type||Disk Type||Consideration|
|23||Stabilization Time (ms)||35||32||This is the upper gain limit for the disk type.
The vibration-absorption capable disk type can be used without any problems.
|Positioning Accuracy (mm)||0.014||0.014|
|Repeated Positioning Accuracy (mm)||±0.002||±0.002|
|32||Stabilization Time (ms)||8||Occurrence of Hunting||This is the upper gain limit for the vibration-absorption capable disk type.
The disk type is not usable due to hunting.
|Positioning Accuracy (mm)||0.016|
|Repeated Positioning Accuracy (mm)||±0.001|
Eccentric Reaction Force
Thrust reaction force
Change in static torsional stiffness due to temperatureThis is a value under the condition where the static torsional stiffness at 20°C is 100%.
The change of XGHW-C in torsional stiffness due to temperature is small and the change in positioning accuracy is extremely small. If the unit is used under higher temperature, be careful about misalignment due to elongation or deflection of the shaft associated with thermal expansion.
Productivity and Stabilization TimeIn a production facility which uses servomotors, single-axis actuators and ball screws, the key to improved productivity is operating these components accurately, as directed by a program. However, occasionally the command execution may be delayed.
For example, when trying to stop the actuator at a predetermined position, sometimes it will stop later than the command, which we refer to as a delay in stabilization time. Since the operation does not shift to the next process until the actuator completely stops, it is important to shorten stabilization time and thereby improve productivity.