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Smart sensor regulates the nominal speed of air motors

Smart sensor regulates the nominal speed of air motors
Developed originally as a solution to assure safety of an agitator within the chemical industry, Deprag's intelligent speed control system for air motors could bring a new level of sophistication to other agitator applications and to broader air motor tasks.

A motor needs to be powerful while still being small and robust, so there are many applications where the size and mass of air motors are convincing advantages. When compared with an equivalent electric motor, an air motor is only one third of the size and one fifth of the mass. That makes it an excellent choice in both hand-held machines and fixed equipment. 

Also motors for sectors such as the chemical industry or the food industry have to conform to stringent safety and/or hygiene standards. Being non-electrical, air motors are inherently suited to such tasks, and can be made from materials that are un-reactive to cleaning solvent and which allow oil-free operation in clean-room environments.

However if there was a weakness then it has always been speed regulation. But that is no longer the case, because Deprag Schulz has developed an innovative speed regulator offered for its air motors, ensuring that the motor will always hold the desired, preset speed.

Product manager Dagmar Dübbelde explains: "It is characteristic for an air-motor that it can be operated in a wide spread of changing loads. When operated without load, the motor runs at its rated no-load-speed. If the load increases, the speed of the motor decreases. Depending on the load, the air-motor can be operated at approximately 15-100% of its nominal speed. Speed also varies with torque."

This can cause problems. Consider an agitator or mixer, for example, where a constant speed is a prerequisite for an accurate production. If the viscosity of the mixture or its volume changes in the container, the speed will inevitably change. This was just the scenario that Deprag set out to address, resulting in the development of the new speed regulator.

The new Deprag speed regulator offers simple and reliable operation. A non-contacting speed sensor is integrated directly into the air motor, between the motor and the gearbox. The sensor monitors the speed and sends a digital output to the regulator, where the desired speed can be easily set. The regulator compares the pre-set value with the actual value, and sends a control signal to a valve if there is a difference in the values, which regulates the air flow. This closed system ensures the air motor operates consistently within the required speed range. 

The speed regulator was developed for a specific customer within the chemical industry, for an agitator mixing liquid chemicals and solutions. The agitator is used with an impeller mixer or an impeller blade, powered by compressed air. Dübbelde comments: "Many of our new ideas are the direct result of conversations we have with our customers. This particular application requires a constant speed to assure the required quality of the product. Our engineers started to look for a simple solution to develop a reliable speed regulator."

The motor used on the agitator has a nominal speed of 1,250rpm. The no-load speed is 2,500rpm and the nominal torque is 9.2Nm. The technical specifications are based on an operating pressure of 6-bar. The speed-controlled air motor operates the agitator for a mixture in the viscosity range of 1-300mPas and maintains its speed within the required tolerance range - independent from fluctuations of the viscosity or the mixture volume within the receptacle. 

Although developed for a specific agitator application, the speed regulator is equally suitable for a range of other tasks. Dübbelde says: "Some processes focus more on the regulator speed and others on the accuracy of the regulator. Our speed regulator can be made to operate for both of those applications and is therefore universally functional." In the case of the agitator, speed of response to fluctuations is less important than maintaining a high speed-accuracy to assure product quality. The regulator is able to maintain a constant speed of +/-5rpm with respect to the nominal set value, correcting the speed within a maximum of 2 seconds if the load changes.

The speed regulator is able to maintain consistent speed even at very slow rotations, evaluating speed against the nominal value at anything from a full rotation to 1/32 of a rotation. It is also suitable for use at speeds up to 80,000rpm. The proportional regulator-valve has a high resolution and so affords very precise control. Dübbelde concludes: "With the addition of speed regulators, problems with air motors due to speed fluctuations during a process are now a thing of the past."
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