Optimizing Delta Pick-and-Place Robot

Annual North American consumption of candy per person is nearly 25 lb. Therefore, chances are you have eaten tiny sweets out of fancy boxes which were placed there by the packaging industry's most successful rapid transfer robot — the Delta robot. Developed in the 1980s, the Delta robot design is the most pervasive rapid transfer robot design on the market with applications in the packaging, medical and pharmaceutical industries. With pick-and-place systems consisting of up to 20 such Delta robots handling 100 to 2,500 products per min, there are a lot of sweets to go around.

The continual need for rise in productivity with robotics is met with various challenges. High reliability, low maintenance, redundancy and equable robot utilization are some of the key performance aspects manufacturers face. These challenges cause OEMs of the Delta robot to continually look for ways to improve their design — seeking optimization of components to provide the best solution. A prime example of such redesign can be seen with the Bosch Sigpack Systems Delta robot. Alpha gear drives and WITTENSTEIN motion control, both members of WITTENSTEIN, supported the Delta robot's new design with advanced components and utilization of cymex^®, WITTENSTEIN's proprietary servo sizing software. WITTENSTEIN and alpha were able to reduce the robot's space envelope and increase throughput.

The Delta Design

The basic idea behind the Delta parallel robot design is the use of parallelograms which allow an output link to remain at a fixed orientation with respect to an input link. The use of three such parallelograms completely restrained the orientation of the mobile platform which remains only with three translatoric degrees of freedom. The input links of the three parallelograms are mounted on rotating levers via revolute joints.

The revolute joints of the rotating levers are actuated in two different ways: with rotational (dc or ac servo) motors or with linear actuators. Making the Delta robot ideal for pick-and-place applications, the fourth leg is used to transmit rotary motion from the base to an end-effector mounted on the mobile platform.

The Delta robot of Sigpack Systems was originally designed using linear rack and pinion actuators. This design proved to be less than optimal. Key improvements which needed to be addressed include:

• High maintenance due to the openness of the rack and pinion/linear actuator design,

• Performance of less than optimal,

• High assembly times,

• Heavy weight of the robot,

• Less than optimal control and accuracy.

The new design was developed for maximum functionality and a 75 percent reduction of components. This design called for a motor-gearbox combination with an integrated lever arm — providing the optimal solution of having all the drive components enclosed and protected against water and dust, reduction in space envelope and weight and improved performance.

The Delta Redesign

The Delta robot redesign was to replace the existing linear rack and pinion with WITTENSTEIN motion control's compact motor-gearbox system with an integrated lever arm. Ideal for Sigpack, the TPM servo actuator is comprised of a high-precision gearhead, a high-pole motor and feedback all integrated into a single package. Because the actuator concept eliminates any extra components, the space and weight envelope reduced by 50 percent. By design, this new solution eliminated the additional rotating parts that are used in a conventional solution, i.e. additional bearings, couplings and larger shafts, which lead to decreased inertia of the actuator. The source of power in an electromechanical solution, the magnets, is moved closer to the load which improves stiffness and results in higher dynamics. Assembly time was reduced and controllability improved.

With reduction in components and optimized factory design, the mechanical design now consists of:

• The robot frame,

• Four motor/gearbox units,

• A few carbon beams.

Comparison of both solution specifications points to the new Delta design (XR31) as vastly improved.

With productivity and efficiency becoming increasingly important, the redesign concept of the Delta robot utilizing alpha and WITTENSTEIN components as integral system improvements created the optimal robot for your sweet desires. So, the next time you have some tasty chocolate treats out of a fancy box, think of the Delta robot and the compact servos that placed them nicely in the box — at about 150 pieces a min for each robot in the system.

Alpha gear drives and WITTENSTEIN motion control are both members of the WITTENSTEIN Group of companies, recognized globally as a leader in motion control.