Mother / Daughter Cart System Basics
What is a Mother / Daughter (M/D) Cart System?
A Mother / Daughter cart system is a system that “captures or contains” individual carts (the Daughters) in a Mother cart that typically accepts (1) or (2) Daughter carts into its frame. These systems allow for quick connection/disconnection into a train that would otherwise be separately connected with a towbar and hitch and moved. The Mother cart is then towed individually or in a train with other Mother carts between the market and plant floor work cells. Mother / Daughter systems can be designed to utilize existing customer carts/baskets as the Daughters or a complete system can be engineered with both the Mother and Daughters designed for specific applications.
Why Use a M/D System?
The M/D system is essentially a cart in cart. Accessing the Daughter is as easy as lifting a bar stop, dropping a ramp, pushing a button or stepping off a pressure mat in the tug. This eliminates the ergonomic challenge of connecting and disconnecting a towbar and hitch and maneuvering remaining carts in the train. The Mother train typically stays connected and is nearly always in motion. Where sequenced loads are required, individual carts do not have to be loaded in exact order. Typically, just a few Mother carts can support a large number of Daughter carts. By making the Daughter carts relatively simple, substantial savings may be realized vs a towable design.
What Design is Right for My Application?
Designs can be separated into two fundamental categories: Mother carts that contain the Daughter carts on the floor (capture or corral) and Mother carts that lift the Daughter carts off the floor in some manner.
Corral or Capture Mother carts are generally useable if the Daughter carts have towable wheels (ones that can be towed loaded at 3-7mph preferably inside the plant w/o failure) and the load weights are less than 800-900 lbs. If so, the design and flexibility of the Mother depends on whether the Daughter carts have (4) swivels or (2) swivels and (2) rigid wheels, the minimum size of the aisle to aisle turns that must be traveled and if indoor and outdoor operation is necessary.
Lift Mother carts come in several configurations as well and are the only solution if the wheels on the Daughter carts are not towable, if the wheel layout does not easily lend itself to a corral orientation or if the loads are over 900lbs. Lift Mother carts may employ single side or double side drop ramps, low friction slide ramps, in-frame roller assist, hydraulic lifting of the Daughter carts directly or hydraulic lifting of the entire Mother cart frame. The design and flexibility of the Mother depends on the minimum size of the aisle to aisle turns that must be traveled and if indoor and outdoor operation is necessary.
How Do I Decide on the Correct System?
If you are just considering a M/D system the first exercise is to challenge your team to consider why you need the M/D over a conventional tugged/train cart design. In many cases a 2-3 cart train with a simple cart exchange format is the best solution. Otherwise, because of the myriad of variables to consider it would be most beneficial to contact a viable designer of both traditional and M/D cart systems such as K-TEC. A typical solution process would involve the answering of a specific questionnaire designed to gather key decision data, a possible follow up visit to the plant to further refine data, comparison of past best practices solutions with pictures and drawings (where possible), visit to a customer’s plant to observe similar applications and finally recommendations and concept design.
Investment in a long term lean material flow solution is a key and critical step in the expansion lean operational path for any plant. It should be approached with the help of experts who are engaged in the business of designing and building lean flow systems and can support the plant in maintenance and further expansion long after the first sale.