DS-APR22-PG44_Layout 1 14/04/2022 09:26 Page 1


FEATURE CLUTCHES, BRAKES & COUPLINGS Miniature motor


applications use DC motor technology – and stopping, slowing


or holding the position and load of these


motors is crucial for a range of applications. This control is achieved by integrating an


electromagnetic brake, as Louis Mongin, BLDC product strategic


manager at Portescap, explains


in miniature DC motor applications. Without a brake, a motor would continue to rotate without control, even after cutting its supply of voltage or current, or it would fail to hold position against a competing power. To hold a DC mini motor in position at a specific


E


stopping point across industrial and medical applications, the general design includes a fixed field coil that acts as an electromagnet to generate torque to brake or hold the load. The coil’s electromagnetism controls an armature that either engages or disengages with a structure. The design of the brake mechanism features a hollow shaft mounted onto the shaft of the DC motor, which gives compact integration. Brakes are available in a power-on design,


which means that the brake is only engaged when current flows in the field coil. This is acceptable when the brake doesn’t have to hold a high load, or if holding torque isn’t required after power-off. Alternatively, with a power-off brake, the brake remains engaged at all times unless current is flowing in the electromagnet, which creates an inherently safer design for some applications. Spring-set brakes utilise power-off braking and


are used to automatically stop and hold a load in the event of a power failure or emergency stop situation. Here, braking force is applied through a compression spring, and the brake is usually released by manual control. The advantages include repeated braking cycles from full motor speed with no torque fade, and the designs can be customised in aspects such as voltage rating and dynamic friction material according to the spring force requirement. The disadvantage is that they


4 design soLutions APRIL 2022 4


lectromagnetic brakes are used to hold, stop or slow down a load


IntegratIng brakes In


mInIature motor applIcatIons


can present backlash, affecting the precision they can offer for dynamic braking or position holding.


permanent magnet brakes


For applications where dynamic stopping and holding a moving load is required, as well as for high cycle rate stopping, a permanent magnet power-off brake should be used. In this design, brakes are engaged magnetically and disengaged electrically, providing safe load holding in power shut-off. When voltage or current is applied to the brake, the coil


becomes an electromagnet and produces magnetic lines of flux counteracting those of the permanent magnet. This releases the armature, creating an air gap and allowing the load shaft to rotate. Increasing voltage or current also enables braking force


to be controlled with precision, as opposed to the spring brake’s on/off functionality. As the permanent magnet brake design


includes no moving parts, they can operate at very high speeds. Unlike spring brakes, they don’t allow backlash. As heat is generated during dynamic braking, this means that the brake must be correctly sized to deal with friction, load and torque requirements. Permanent magnet brakes require consistent and specific current, meaning that these brake designs should be carefully considered before using them in conditions that could cause current fluctuations, such as high or changing temperatures. Thanks to the precision control of a permanent


magnet brake, they are well suited to use in robotic arm joints; and their zero-backlash capability means they can precisely hold torque and also provide dynamic stopping. An example of a DC mini motor application that requires safety in holding torque is the control of automated window shades. Providing automatic operation, the power-off brake also allows the motor to hold the shade position when power is removed.


portescap www.portescap.com


putting a stop to stage accidents


Most theatre goers fail to appreciate the engineering required to move the lights, scenery and props that contribute to a memorable performance. However one general contractor ensures that its stage equipment is positioned precisely where it’s required thanks to Stromag Series 51 limit switches. Installed above the stage of many theatres is the upper machinery, mostly winches and hoists


driven by motors which raise and lower lights, scenery and props. As these are located above the performers, it’s imperative that loads stop exactly where needed. Marco Niehnus, global product manager controls at Stromag, explains: “The upper machinery


in theatres is similar to a crane application, with loads being moved up and down. Ensuring that these loads stop reliably is critical with performers on stage below. Our Series 51 geared cam limit switches set the upper and lower stopping points of these loads by accurately measuring the number of shaft turns, delivering highly reliable stopping performance.” The Series 51 is suitable for many upper stage


machinery configurations. This includes fly bar drives, which feature a lifting device with steel wires wound around a single drum and attached to a bar or traverse; tubular shaft drives, where each wire is wound around its own drum and can move multiple bars; as well as point hoists, which feature a single wire for lifting. The limit switch can be installed to measure the turns of the motor or the winch drum, ensuring versatility.


stromag www.stromag.com


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58