Jonathan Bullik — Sales Engineer Department of elevators KEB Amerisa, Inc. The last 5 years he has worked in the field of application of the brakes and engine control units. He graduated from the University of Minnesota, St. Paul and Minneapolis, with a Bachelor of Electrical Engineering. Now we are preparing to receive a master’s degree in Business Administration from the same university.
The growing popularity of gearless traction elevators without machine room, in recent years has created new demands on the brakes. To save space, many without machine room arrangements make longer and narrower. The brakes are used in this construction must, having a small diameter, to be able to generate relatively high torque. In addition, mechanisms without machine room can be located within earshot of tenants or employees, so that quiet operation of brakes becomes absolutely necessary. Because the engine is not always easily accessible, attention is installing a reliable brake that is easy to manage and maintain. This article discusses the principles of the spring brake to be included from the anchor, and its use in gearless elevators without machine room.
Advances in technology allow the production of ropes used in the gearless lift mechanism without engine room (BMP) of smaller diameter pulleys all. Drum and disc brakes are particularly effective for larger diameter pulleys and brakes DC included from the anchor, become the preferred technology for gearless systems BMP. In addition to ensuring the smooth inclusion of the brake when power failure in the DC brake is used robust design with only one moving part. There are models with a mute, who work almost silently. Furthermore, the brake come in several variants, and can easily set the configuration according to the specific technical requirements of the system. There is room for excessive engine brake BMP obtain certification of protective emergency brake — it was impossible for conventional gear configurations.
The theory of action.
In 1820 Hans Christian Oersted found that the current through a wire creates a magnetic field around the conductor; This phenomenon will explain later Ampere’s law. Shortly thereafter physics know that if the wire to be wound on the iron core coil is substantially concentrating the induced magnetic field. They found that the strength of the magnetic field produced by the inductor is proportional to the number of coil turns and a current is passed through it. The results of these studies led to the creation of an electromagnet — a magnet which can be obtained by passing an electric current through the coil.
Electromagnetic spring brake consists of a DC electromagnet having a magnet and a coil body. The magnet is typically attached to the end cover of the engine by means of adjustable screws. Several compression springs arranged in recesses in the front surface of the magnet loaded so that spring force acting on the non-rotating anchor. With the help of splines friction lining is connected to the shaft sleeve and is located between the anchor and other convenient friction surface. For axial location of the sleeve a small air gap between the magnet and the anchor is regulated by means of fixing bolts to maintain a certain distance between them.
Turning the power off (including brake).
In the scenario steady state (power off) to the coil of the electromagnet is not supplied DC voltage, so that there is no current, and does not create any magnetic field. When the spring force applied to the armature, the friction pad is clamped between the armature and a friction surface generated torque, the retaining shaft in a stationary position.
Power (brake off).
When the coil is energized, current flows and a magnetic field. The magnetic field continues to grow so long until it becomes so large that the magnetic flux jumps across a small air gap between the electro-magnet and the armature and closes the magnetic circuit. The magnetic force compresses the spring circuit, and the anchor is attracted to the magnet surface. The spring force no longer acts on the friction pad, so that the sleeve and the motor shaft can now rotate freely.
Embodiments of the brake.
One of the advantages of brake dc — its proven reliability. Construction of HMS contains an excessive amount of compression springs, each of which is designed for more than 10 million cycles. The coil is completely sealed with epoxy, it uses wire class H high-friction linings are used that are resistant to clogging and damping torque. Anchor — the only moving part of the brake, so that it no levers or connecting elements, which may break both brakes AC. Another advantage of the spring brake dc — flexibility of its design and the availability of other options. Below are some common features that are required when using the brakes in elevators.
Hand off the brake.
The manual allows the operator to disable the brakes open the brake, not giving energy to the solenoid coil. This feature is primarily used for testing and troubleshooting, but can be used in emergency situations. A manual device off the brake consists of a collar and arm, which are attached to the rear surface of the housing of the electromagnet. Fixing bolts pass through the clamp and the body of the electromagnet and capture the anchor. When the lever of a manual brake opening retracted, springs are compressed electromagnet and the armature is drawn in through an air gap, allowing the friction lining and the shaft to rotate freely. For safety requires that the lever was applied constant force or «constant effort» to keep the brake open — if you let go of the handle, the brake on.
To elevator controller important function is the possibility of monitoring the condition of the brakes. Verification of the state of the brake system increases safety and optimizes timing control sequence. Feedback from the controller provides brake to ensure that the brake will not be activated at any point during normal operation. Turning brakes until the cabin has not completely stopped, or the inclusion of the motor before the brake is fully released, resulting in premature wear and shorten the life of the brakes. Brake microswitch provides feedback signal showing the state of the brake — on or off. Typically, the configuration of the microswitch is that it closes when the brake is fully released. One of the ways to install micro — putting it into the machined recess in the housing of the magnet. Also, attached to the armature plunger, its length is adjusted so that it is directly over the switch. When the armature passes through the air gap, the plunger moves with it and presses the switch by closing the contact. It is important to use industrial-grade switch that is able to withstand repeated cycles of the elevator at work.
Construction noise canceling.
Brake DC creates an audible sound when activated armature, which thus enters into contact with the body of the electromagnet or the friction lining. The sound of metal hitting metal when disconnecting the brake is particularly noticeable at larger sizes brakes. For larger brakes require more anchor that allows a greater flux. The increased weight of a larger anchor has greater kinetic energy, producing a loud sound at contact.
HMS Company uses mainly two methods for noise reduction in DC braking. In the first place the need to design sound-absorbing material between the electromagnet and the armature. Such material must act as an insulator between the two metals, and absorb energy of a moving armature. However, it deserves special mention the possibility of a guarantee that the anchor is fully pressed against the magnet and there will be no residual torque generated by the friction disk. This method softens the metal to metal contact, but it reduces the noise only when the brake is released.
The second sound absorbing structure of the elevator brake provides a reduction speed of the armature. Since the duration of the actual operation of the armature is so small it has no appreciable effect on the overall synchronization of the brake. The advantage of this solution is that the noise level of the brakes is reduced, and when it is turned on, and when it is turned off. Absorbing elevator system with a special design of anchor developed by HMS, it is designed for a standard level of less than 65 decibels at a distance of 1 m. If necessary, additional structural solutions can reduce noise to less than 55 decibels at a distance of 1 m.
Excitement and switching to low voltage.
Note that DC braking inherent delay when switching to the time from applying a signal to the brake prior to the creation or reduction of the torque. This is due mainly to the fact that for switching on or off the brake or damping capacity required of magnetic flux in the electromagnet, and it does not happen instantaneously. Delays in switching even more often in large brakes because of the higher inductance of the coil and the magnetic field to be created or removed.
One of the solutions to reduce delays when the brake is released, it is over-or short-term supply of the rated voltage, as long as the anchor begins to retract. The air gap creates a resistance of the magnetic circuit and the required maximum value of the magnetic flux to jump the air gap, creating a magnetic circuit with the armature. Once the anchor is pulled in, the magnetic flux needed to hold it in place, is greatly reduced. At this point, the voltage applied to the brake, you can return to the nominal value. Such a switch from overexcitement helps increase the magnetic flux, but only reduces the response time when releasing the brake.
Time of the brake can be improved by holding the brake in the released state with lower voltage. As mentioned above, as soon as the anchor is pulled through the air gap, it can be held in place with a much lower voltage. Holding the lower voltage means that there is little magnetic flux circuit, which must be removed to force the anchor springs back to its static position. Similarly, switch to the excitement, there are special brake switches, which can keep it at a lower voltage, thus reducing the time of the brake. Depressing the brake in an open condition with a smaller voltage also corresponds to a lower and less heat loss on the coil during its lifetime.
Construction of double brake.
As the brake is critical for the safety of the elevator, the system requires some redundancy stopping power. The nature of such redundancy requirements may vary depending on the existing technical requirements and guidelines. One of the most common in the world is the directive DIN EN 81 «Safety rules for the design and installation of lifts.» Part of the Standard EN 81 relating to the electric lift, says that in the electro-mechanical brake must be two independent sets of mechanical components that could impede the cabin. Since this applies to the brakes with the activation of the anchor, there are several different ways to design and use of excessive brake systems.
Type DDN — double brake.
One way to create a redundant braking system — the use of two independent brakes. This yields two separate electrical and mechanical systems. Brakes are often drawn together and shipped by the manufacturer, ready to install with flanges and pre-installed air gaps. The dimensions of the brakes must be such that each individual brake can stop the lift in accordance with the applicable standard. In addition, separate electrical circuits mean that the brakes can be controlled by a separate safety controller circuitry, and this further enhances the redundancy of the system.
Type D8 — design with a split anchor.
One way of reducing the overall size and cost of the dual brake of the requirement of separate mechanical braking components is to use a split structure of the armature. The brake uses a common magnet and a half two separate anchors or «split anchor.» Each anchor has its own set of springs, and it is able by itself to slow down the movement of the car. The advantage of this solution — the overall length of the brake is smaller than that of the composite dual brake. Moreover, the design with a split anchor uses significantly less material, hence it is more economical than the present dual brake. The design allows all options D8 — two anchors can be fitted with individual handheld devices and microswitch for release monitoring.
Emergency brake in case of overspeed when lifting the cabin.
The DIN EN 81-1 requires a means of detecting the situation of excessive speed when lifting the elevator car and slowing its movement. In traditional geared elevators electromechanical motor brake can not be considered an emergency braking device when lifting cab speeding, because it is not directly connected to the drive pulley. Because the mechanisms of gearless without machine room brake and put the pulley on the same shaft, the engine brake can be regarded as an emergency brake, if it is properly used. This is important, since engine brake may replace the cable grip or brake pulley, acting as a safety brakes, thereby saving space and money. And double brake (DDN), and brake anchor split D8) of HMS certified by TÜV as allowed for use as a safety brake when lifting elevator speeding to EN 81-1. Customers should ask their manufacturers of engines and brakes, so they presented the results of tests or certificates of independent inspection, indicating that the brake meets the technical requirements for the emergency brake.
Elevators without machine room have clear advantages in terms of space requirements and efficiency compared to conventional designs, so they will continue to spread. Engine brake — very important component of the design of the mechanism without machine room, it can contribute to the compactness of the system and its ease of maintenance. Spring-action brake with the inclusion of an anchor — a proven solution, wherein a small number of components that can fail, and long life. These brakes can even be certified as emergency brakes, replacing the more cumbersome and costly system. In short, the spring brake DC meet the strict requirements for security and functionality for use in elevators without machine room and are a viable solution to the problem of inhibition.