192 clutches and power-stop control – Clutch and brake
Reexamination Certificate
2000-04-13
2001-12-25
Marmor, Charles A (Department: 3681)
192 clutches and power-stop control
Clutch and brake
C192S048920, C192S056540, C192S056200, C192S0120BA
Reexamination Certificate
active
06332518
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a rapid-response braking device for braking a machine-driven part.
One of the problems in high-speed stamping and bending machines consists of preventing or limiting, as far as possible, damage to the tool in the event of an excessive load which is placed on the tool. Thus, it is known to use an overload clutch which separates the drive line of the motor from the tool if the scheduled load is exceeded (torque) or, with respect to a slipping clutch, which limits the torque transmitted by the drive shaft. Because of the momentum which the masses behind the overload clutch have, they continue to rotate when the overload clutch responds, even if it completely releases the masses from the motor in the drive line. The problem to be solved therefore consists of braking the continuously moving masses as quickly as possible so as to prevent them from causing any major damage. If a brake is provided between the motor and the overload clutch, the brake may brake and stop the motor, but not the section of the drive line which is released by the overload clutch and which connects with the tool. However, if a brake is provided behind the overload clutch, it is possible to brake the tool until it comes to a standstill and thus prevent damage, provided that the brake is fast enough. Unfortunately, the masses that have to be braked in the drive line behind the overload clutch (tools and gears) are generally larger than the masses which lie in the section of the drive line in front of the overload clutch. A brake provided in the drive line behind the overload clutch must therefore be provided with a respectively strong design, which has an adverse effect on the braking times. The braking time is made up of an excitation time which is characteristic for the design of the respective brake and of the pure braking time for dissipating the kinetic energy. Pneumatic and hydraulic brakes require higher excitation periods for driving valves and for building up the required pressure in the braking device than electromagnetic brakes. However, they can provide large braking moments. Fast control devices such as electromagnetic brakes allow for a very short excitation time of the brake coil, but provide a longer braking time. A short braking time is of importance in stamping and bending machines and, in particular, in machines for trimming and forming the legs of integrated circuits (IC) in which the tool is driven by a cam gear, i.e., the forward and backward movement is determined by a roller which rolls on the cam surface of an eccentric disk. A rotation of the eccentric disk is equivalent to one work cycle of the machine in which the tool is positioned, the position being controlled such that the tool is advanced for processing the workpiece (working stroke) and then retracted (idle stroke), and the workpiece is advanced or removed. It is known from experience that the control of the tool movement requires about half a turn of the eccentric disk. Thus, only half of a turn of the eccentric disk is available for conveying the workpiece, for positioning the workpiece, for controlling measurement for ensuring that the tool position is correct and for a possible switch-off of the machine if the workpiece position is incorrect. The extension or shortening of the brake angle thus finds entrance into the cycle time of the machine with a factor of up to 2, i.e., the extension of the brake time causes a considerable extension of the cycle time. In order to obtain high-speed machines, it is therefore decisive that the workpiece can be stopped very quickly so as to prevent the destruction of the tool in the event of a wrongly positioned workpiece. Until recently, this problem was addressed by improving the efficiency of the brakes, reducing the response times and placing the brake as closely as possible to the position to be protected at the end of the drive line. These measures were implemented so as to provide a reduction of the maximum occurring moment that is caused by the released mass moment of inertia. These attempts, however, are subject to certain limits, because high braking moments are required through larger braking devices whenever high mass moments of inertia are present.
SUMMARY OF THE INVENTION
The invention is directed to a device for braking a motor drive machine part which can provide a particularly rapid stopping of the driven machine part by intentional braking during malfunctions, and which limits the maximally occurring moment in the event of overload and thus the maximum load peak acting on the tools.
In accordance with the present invention, there is provided in the drive line, between the motor and the driven machine part, a combination of a brake, an overload clutch and a freewheel which runs freely during the driving of the machine part, but which blocks during the braking of the driven machine part. The brake in the drive line is disposed in front of the overload clutch and the freewheel is disposed behind the overload clutch.
If the brake operator is initiated or operated by a sensor which reports that a workpiece on which the driven machine part (tool) is to act is not positioned correctly, the momentum of all moving masses at first acts on the brake and the torque threshold is reached very quickly by the braking process, whereupon the overload clutch responds. At this time, the brake does not have to brake the masses disposed behind the overload clutch for the short period until the blocking of the freewheel occurs. It only has to block a very small mass, so that the brake comes to a standstill very rapidly. The response of the overload clutch does not, however, lead to the situation that the released machine part can continue to move unhindered, because the freewheel now automatically takes affect. After passing its clamping angle, which should be very small, the freewheel blocks and receives the remaining momentum of the driven machine part (tool) that is to be braked. It then passes the momentum into the brake which, because it is now static, dissipates the energy practically instantaneously. The holding momentum of the brake is so high that it is not necessary to put the drive shaft into motion again. Here, the blocking direction of the freewheel is equivalent to the driving direction.
If the brakes are not intentionally activated and there is an excessive load in the drive line such that the torque threshold of the overload clutch is exceeded, the freewheel responds. In accordance with the invention, this can be used to release the braking device. The braking device can stop the drive shaft very rapidly because the freewheel does not initially block at first, and thus the momentum of the moving masses behind the overload clutch is not stopped, but the momentum in front of the overload clutch is caught and requires braking. Therefore, it is possible to provide the brake with a relatively compact design, i.e., with a small end brake coil, additionally in contributing to a short braking period. The mass to be braked during this phase is particularly small if a clutch for decoupling the motor is provided between the brake and the motor. In this case, the brake does not have to also brake the flywheel mass of the motor in the event of a response by the overload clutch. Preferably, the additional clutch is provided in the form of a clutch-brake combination, i.e., a component consisting of clutch and brake, which provides a minimum of masses to be braked by using a compact design. Because the mass to be braked by the brake is very small, it comes to a standstill very quickly. The braking of the freewheel also occurs very rapidly. The blocking freewheel collects the remaining momentum of the masses in the drive line behind the overload clutch (tool side) like a buffer and transmits the energy into the already static brake. The holding moment of the brake is so large that the drive shaft does not start to move again.
The braking device in accordance with the present invention is particularly suitable for high-speed bending and stampi
Marmor Charles A
Micro)n Technology, Inc.
Rodriguez Saul
TraskBritt
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