BendVision | real-time analysis of the bending process.

BendVision takes a unique approach to press brake angle measurement and angle control through advanced image processing technology that delivers greater flexibility and accuracy for machine manufacturers and users.

Press brake users have always faced challenges with air bending due to a number of factors including machine beam deflection, variation in material thickness and variations in material grain direction. Even when a bending job is set-up and program corrections have been made for the machine to produce the desired angles, variations in material thickness and grain direction from one part to the next can still cause issues with angle accuracy and consistency.

So, what are the options for machine operators?

The most common method is manually checking and measuring angles using a protractor or preset angle reference tool. Depending on the accuracy required for each part, the operator may need to check each part after it has been formed, or periodically check a sample of parts when processing a volume batch. Of course, while this method requires no additional upfront investment when the machine is purchased, there is a much longer-term cost in respect to lost production time that is consumed with manual measurement and checking of parts and the potential for more material wastage.

The second option is to invest in a factory installed angle measurement system when purchasing the press brake. Most press brake manufacturers today offer some form of proprietary angle measurement solution as an optional extra. The two traditional and most commonly available methods have been laser projection sensors and mechanical contact sensors.

The laser projection sensors are generally housed on the front and back sides of the lower machine beam and then project bands of light onto the undersides of the material. These sensors can either be static, where the operator would manually position the sensors to align with the work-piece, or motorised for automatic positioning. Mechanical contact sensors come is various forms that either contact and measure the outside or inside surface of the material. To be effective, both of these types of measurement solutions are integrated into the machine process by the manufacturer and will often include some form of automated angle correction or control.

While these are usually accurate and effective solutions, they are generally also expensive options that need to be carefully considered during the purchase of a new machine. The high cost is attributed to the dedicated optical or mechanical sensors, associated electronics and software, as well as complex motorised mounting systems that are often required in the design of these systems. In a perfect world, all press brakes would include an angle measurement device, however in reality, due to the high initial outlay, they are generally only fitted to a small number of the total machines that are manufactured and sold each year.

The BendVision concept looks to change all that with an alternative and more economical method of measuring bend angles. The technology behind BendVision image processing is incorporated into the hardware of the press brake safety guarding system that needs to be fitted to every press brake by the manufacturer anyway to meet certification and safety standards compliance. The guarding system uses camera technology for optical monitoring of the punch and detection of foreign objects inside the space between the tools during machine operation.

When the press brake is in the fast closing portion of the cycle, the camera system is providing the safety function, however once the punch contacts the material surface to start the bending sequence, the optical protection is no longer active. From this point onwards, the camera is sitting idle until the start of the next machine cycle.

BendVision takes advantage of this idle time by switching the camera function to active image processing where images are constantly taken from the end-view of the machine and processed in real-time.

By integrating with the existing guarding hardware, the process eliminates the requirement for additional components, sensors and mounting hardware that are normally dedicated only for the angle measuring functions. For press brake manufacturers, this combination method is the most efficient and cost effective method of incorporating technology that is capable of generating real-time angle data during the bending process.

BendVision analyses processed images of the material and tools during the bending process and by capturing the material limb information, BendVision determines the inside and outside angles of the part - where both sides are open. From this, the angle of the bend can be accurately determined, taking into account any measured variations in machine deflection. The CNC could set tolerances for deflection to determine if the machine crowning is set correctly or if a crowning correction is required. When the bend angle is closed - for example box bending where the inside angle is obscured - BendVision is still capable of analysing the outside angle of the part and with other visual data will continue measuring the bend angle in real-time.

Real-time angle information is the key to more flexible and powerful angle control solutions. If only static angle measurements are taken, then the press brake bending process needs to be paused while measurements are taken. The measured static angle information is then processed by the CNC or third-party software in order to calculate a bend angle correction. In some cases, it may be necessary to pause and take several measurements and calculate multiple corrections per bending cycle. Of course, this creates delays that, in high-volume processing, can slow down part production.

If the CNC can receive the angle of the work piece measured in real-time, then this opens up a wide range of possibilities. Firstly, having the actual angle at the time of bending, instead of measuring after the part is already formed, means that the CNC can determine when to stop bending in order to prevent a part being over bent and possibly having to be discarded. An under bent angle is fine since a correction and re-hit can be made to continue bending to the required angle.

The benefit of real-time angle information is that it can be used to control bending depth rather than the CNC having to calculate the depth based on the tooling set-up, material type, spring-back properties, material thickness and the programmed angle. Through the use of BendVision, angle control processes have been developed by press brake manufacturers and implemented in many different forms.

The basic premise of real-time angle control is that the CNC will use the live angle information to control the bending process, rather than relying on the traditional method of calculating the control process and bending depth prior to starting each bending cycle. If the spring back value of a particular material is already known, then the CNC can take this value and subtract it from the target angle. For example, if the spring-back is 2.0 degrees, and the target angle is 90.0 degrees, then the CNC can drive the tools until the real-time angle is 88.0 degrees - regardless of the material thickness. Once the real-time angle reaches 88.0 degrees, then the CNC can stop bending and decompress, releasing the material while reading the real-time angle until the material has sprung back and reached full relaxation. At this point, the CNC will see the actual final measured angle of 90.0 degrees provided that the original spring-back value is accurate.If more accurate angle control is necessary, then the spring back properties of the material can also be measured in real-time, rather than

the CNC relying on a predetermined spring-back value. In this instance, the CNC can use a similar real-time angle control process to under bend a part then pause and slowly release the material while reading the live spring-back angle and recording this value. The spring-back value can either be stored in memory and used as a global value for each bend in that particular part or a batch of parts, or spring-back can be measured on each cycle prior to bending to the required target angle. Once the individual spring-back values have been measured and stored for each step of the first part, then these individual values can be used to automatically control bending for all remaining parts in the production batch.The second possibility is where there is an inconsistency in the grain direction from one part to the next in a batch of parts - for example, where the grain direction is different due to the way the parts were cut or if the parts are cut from different material stock. In this case, the CNC can activate real-time spring-back measurement on every bend for every part in the batch.

While this takes a fraction more time per part, the results are far more beneficial with greater accuracy and consistency from one part to the next. This same process can be applied to short run parts or when bending high value materials where wastage must be minimised.While current angle measurement technologies are highly effective and accurate, BendVision makes realtime angle control a simpler and more attainable prospect for manufacturers and users alike with the ability to standardise angle measurement and control rather than it only being available as a high-end option. Angle measurement and angle control processes are productivity and quality control tools that ideally every press brake user should have at their disposal and now BendVision makes these tools more accessible than ever before.

BendVision technology is available with selected leading press brake manufacturers and will be on display at the EuroBLECH fair in Hannover this October.