PNP Speed Update

Since adding the various modifications to the DIY pick and place machine in the past few months we have now been able to tweak the speed and acceleration of the stepper drivers to improve the machine's placement times.

We started by adjusting the acceleration on the X and Y axis, gradually increasing it until the motors began to stall, we then backed it off a bit so they accelerated reliably.  We then did the same with the maximum speed.  Once the X and Y axis were running at their fastest we repeated the same process for the two picker heads.

With the motor speeds set to their maximum, the next stage was to reduce the delays between each movement.  When the picker head comes down to the component the vacuum solenoid is turned on to make the component stick to the needle.  With the original solenoids that we bought from eBay, we had no information to tell us how long it took for the solenoid to switch on so we had to guess and set the delays longer than they really needed to be.  We have recently upgraded the solenoids on the vacuum and the air supply to ones with higher throughput and these solenoids came with a datasheet that showed they took 50 milliseconds to switch on and off so with this information we could update the software to hold the needle down for 50 ms before lifting it again with the component.

All of the tweaking to the speeds and software has meant that the pick and place machine is now about 30% faster than before and we can place components at a rate of up to around 3000 components per hour which is similar speeds to entry-level commercial machines.

The motors and other hardware are now running at their limits with the current design so to make the machine faster we will need to redesign the way it works.  There are several ways we could improve the speed, making the picker head assembly lighter, replacing the belts and stepper motors with ball screws and servos and adding extra heads so we can pick up more components at the same time but the current machine is already building boards faster than we can cook them in our reflow oven so for the time being, we will be leaving it alone.

The video below shows the running speed of the pick-and-place machine after the latest speed improvements in building one of our ADC Pi Raspberry Pi expansion boards.  

The updated code and files can be downloaded from GitHub.