Clutches

The wrap spring clutches of the EC series are ideal switching elements for connecting and disconnecting individual axes that must run synchronously with a main axis. Typical applications for wrap spring clutches are the paper flow in a copier, the feeding or dispensing of banknotes in an ATM or the transport of documents in document scanners, printing systems or mail processing systems, etc. The core of any wrap spring clutch is the precision spring, which must transmit the torque from the input shaft to the output shaft. The manufacturer of the clutches REELL Precision Manufacturing Corp. produces the springs itself and has developed a special process that allows the measurement of the spring characteristics during the production process and thus the adaptation of the parameters still during the production of each individual spring. The result is very tight tolerances in spring production that cannot be achieved by external manufacturers. The special features of the EC series are the compactness, the simple control (on / off) and the low energy consumption of only a few watts for a large transmission torque. Torques from 1.7 to 8.5Nm are offered in three sizes (Ø30.1mm, 33.3mm and 44.45mm). Typical speed ranges from 100 to 800 rpm.

Long Life Technology:
The use of new materials, more precise surface machining and better lubrication techniques have made Long Life versions possible, which are clearly superior to conventional couplings, especially in terms of service life at higher speeds (up to a factor of 10!).  A further improvement was thus achieved in the area of consistency of acceleration and braking times both from clutch to clutch and over the service life, which is an essential requirement with higher throughput and ever smaller document gaps.

Clutch/brake unit:
A special feature is the EC20-CBLL clutch, which in addition to clutch functionality, also offers a friction brake for faster coasting after clutch disengagement.

Mechanical versions:
For customer-specific applications, the wrap spring technology can also be developed as a purely mechanical component - e.g., for the detent-free angle adjustment of backrests.

Mode of operation:
When the stationary coil is energized, a magnetic field is generated, which is used to attract the control ring to a stop. This causes the control ring, which is mechanically connected to the wrap spring, to be the control ring, which is mechanically connected to the wrap spring, is held in place relative to the housing. If the input shaft now rotates in the correct direction, the spring tightens around the hub and, when the spring is tensioned, transmits the torque from the input shaft to the output shaft. Depending on the customer's application, either the shaft or the three-claw adapter can be used as input (output is then the other part in each case). The time for tensioning the spring and thus the acceleration depends on the input speed! If you switch off the voltage, the control ring becomes loose, the spring relaxes and the connection from the input to the output is released and the clutch acts as a freewheel again (which, by the way, it generally does in the opposite direction of active torque transmission!).

Selection in 4 steps:
The following guide is intended to take you step-by-step through the selection procedure for wrap spring couplings. The total load for your coupling is made up of the load friction and the acceleration torque of the reflected inertia. The inertia must not be neglected!!! Since the acceleration of the load mass occurs in less than 3ms, high torques for acceleration result very quickly!
Step 1: Determination of the torque due to friction
The friction torque of the load acts on the output of the clutch. The value for the friction torque can be measured directly if necessary or must be estimated.
Step 2: Calculate the load inertia
Calculate the reflected load inertia at the output shaft of the coupling. As an approximation it is sufficient usually the division of the load into different cylinders.
Step 3: Determine the acceleration torque due to inertia
In order to calculate the acceleration torque due to load inertia, one needs the system speed in addition to the inertia information from step 2. This allows to determine an estimated value for the acceleration torque from the following graph (in case of different velocities of single system components, the value for each component has to be determined and the sum has to be calculated!)
Step 4: Determining the total torque
The total torque is the sum of steps 1 and 3. Then select the correct coupling from the table in the data sheet. Flexible coupling elements and slip couplings can be used to improve the service life and reduce noise.