Multi Pick

Under construction May 19, 2021

Summary

The topic of this article is the Multi Pick functionality in Pally. In short what the functionality does, when, why and how it should be applicated.

Table of Contents

What is Multi Pick

The Multi Pick functionality does exactly what is sounds like, and allows to pick up multiple units of product at a time. Thus, palletize more than one unit each cycle. This is beneficial in numerous ways. To be able to discuss how and why effectively, there are two important acronyms to understand:

  • CPM
    Cases Per Minute: The amount of cases/ product units/ boxes to palletize each minute.

  • Cycles/min
    Cycles Per Minute: How many palletizing cycles are performed each minute. A cycle is defined as an entire pick and place task, i. e. from starting the pickup when the product(s) is ready at the pickup position, to place the product(s) on the pallet, to finally return to the waiting position.

Benefits of Multi Pick

The benefits of picking multiple units are many, as long as the payload, integrity and the shear size of the product allow it for the specific palletizing system.

Palletize More Products per Minute

At production lines where the required CPM is higher than the available cycles/min, Multi Pick is often a good solution.

Example
If a line operates at 20 CPM, which is twice as high as the plausible cycles/min for a UR10, the palletizing can for instance be done at 5 cycles/minby using Multi Pick to palletize 4 products per cycle.

Increased Reach

When palletizing small products, the further most corner of the pallet may be hard to reach, depending on the robot, the gripper, the pallet size and distance from the robot base. A system engineered for Multi Pick will often utilize a gripper that provides a certain offset between some of the products and the robot tool flange, which in term can be used to increase range.

Increased Safety

Given that the products can be gripped and moved in a safe manor, Multi Pick will increase safety because the robot can operate at lower speeds. The more product units a robot is allowed to palletize per cycle, the fewer cycles/min can be while keeping CPM up. Thus, a cycle can be allowed to take more time, enabling speed reduction.

The Physics
When an object is moving, the kinetic energy of the object is quadratic (exponential with the factor of 2) to the velocity, while only linear to the mass. Thus, if velocity can be reduced by increasing mass (pick more units), it will decrease the amount of kinetic energy in the palletizing system significantly. Hence, the kinetic energy dissipated in a collision is also reduced. With less energy to dissipate, the impact force between the product and the object or personell it collides with is reduced. This effect is increased even further by taking the mass of the robot and the gripper into account, making Multi Pick even more advantageous. A unitary representation how kinetic energy increase with mass and velocity can be seen in the graph below.

 

How to Multi Pick

Engineering the System HW

While Pally accommodates Multi Pick, the system HW must be engineered to do so. That being said, most palletizers running on Pally can Multi Pick. How many cases in each pick is depending on:

  • Product Sensors: One sensor is needed per unit to pick.

  • Payload: The gripper must be strong enough to grip the product, and the robot strong enough to carry it.

  • Size: The gripper must be able to get a firm grip on all of the units in each pick.

Product Sensors

Each product unit to be gripped in a single pick must have a dedicated product sensor. These sensors are necessary to keep Pally informed of how many products are available at the pickup position. Thus, if a maximum of four units are to be picked each cycle, the line must be equipped with four product sensors.

Example
In the image below a very standard Pally palletizing system is displayed. It utilizes a UR10 robot, two product sensors and a Unigripper Co/Light gripper. Due to the two product sensors, this setup can Multi Pick up to two products each cycle.

A standard Pally HW setup with two product sensors. Thus, this setup can Multi Pick up to two cases each pick.

Payload

The payload of the product and the gripper will in many cases be defining for how many products can be palletized at once. To grip more products in a single pick, a greater gripper might be necessary, potentially increasing gripper weight, thus reducing the amount of product in the payload.
Multi Pick can often be used with a standard gripper like the Schmaltz FXCB or Unigripper Co/Light. In other words; A palletizing system, even though it is not customized specifically for it, can Multi Pick products, depending on the payload and product size (see subchapter below on gripper size and grip quality).

Example 1
A UR10 has a maximum payload of 10 kg. If each box weighs 0.5 kg, and a big enough gripper weighs in at 2 kg, up to 16 boxes can be picked at once.

Example 2
In the image below, a UR10e fitted with a Schmaltz FXCB foam gripper is simulated to pick two cases at a time. The case size of this product in particular allows the gripper to grip two at a time, splitting the gripper area 50/50 between them. Since the gripper weighs 1.85 kg and the extra mounting bracket weighs 0.15kg, the remaining payload available for the product is 8 kg. Hence, each case can weigh up to 4 kg.

Schmaltz FXCB Foam picking two cases.

Gripper Size and Grip Quality

The gripper chosen for the project must of course be big enough to reach all the product units in each pick, but also provide good grip quality to safely palletize them. Good grip quality is mainly a product of two features: Strength and stability. Not only must the gripper be strong enough to carry each unit of product, but also provide sufficient stability during the movements.
Just like it is mentioned above, regarding Payload, most palletizing system using Pally can Multi Pick. When the HW is installed it is really only dependent on the specific product size and payload whether Multi Pick can/ should be applied or not.

Tell Pally to Multi Pick

The Multi Pick functionality is native in Pally. Whether to use it or not is configured in each pallet pattern. This is done by defining how many product units Pally is allowed to pick each cycle. If it is necessary to pick fewer units in one or more cycles to complete the pattern, Pally will automatically do so.

It’s recommended to apply zero box padding for a pattern using Multi Pick. This is to ensure even space between the products on the pallet. If some padding is necessary, instead try to compensate by increasing the box size in the pattern.

Pallet Pattern Setup for Multi Pick

In Pally Pallet Builder

Navigating to Advanced Pallet Builder → Settings → Multi grip in Pally Pallet Builder (https://palletizer.rocketfarm.no/home). The field “Max grip” decides the maximum amount of products to be gripped in each pick. Please do remember that it is recommended to set “Box padding” to 0 if “Max grip” is set higher than 1.

 

In Pallet Pattern .json file

It is also possible to edit the pattern file directly to enable Multi Pick.

  • Open the pallet pattern .json file in a text editor.

  • Find the parameter “maxGrip” and edit the adjacent number to the maximum amount of product units Pally is allowed to pick per cycle.

  • If “maxGrip” is set to a value higher than 1, it’s recommended to set the parameter “boxPadding” under “guiSettings” to 0.

Example
Using the example snippet of a pallet pattern .json file below, named “myMultiPickPattern”, Pally is allowed to pick up to three product units per cycle due to the parameter “maxGrip”: 3.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 "name": "myMultiPickPattern", "description": "This pattern can pick multiple units per cycle", "dimensions": { "height": 1000, "width": 800, "length": 1200, "palletHeight": 144 }, "productDimensions": { "weight": 2500, "height": 200, "width": 190, "length": 290 }, "maxGrip": 3, "labelOrientation": null, "guiSettings": { "PPB_VERSION_NO": "2.3.1", "boxPadding": 0, "units": "metric", "overhangSides": 0, "overhangEnds": 0, "altLayout": "mirror" }, ...